A recent study by Liu et al.(2020)suggested that due to the saturation of equatorially trapped planetary waves with different dynamical types,temporal periods,meridional and baroclinic modes,complex layer structures o...A recent study by Liu et al.(2020)suggested that due to the saturation of equatorially trapped planetary waves with different dynamical types,temporal periods,meridional and baroclinic modes,complex layer structures of vertical velocity shear and hence turbulent mixing could frequently occur in the thermocline of the eastern equatorial Pacific.We investigated the occurrence of the interior turbulent mixing as indicated by shear instabilities,above the Equatorial Undercurrent(EUC)core at three equatorial sites along 140°W,170°W,and 165°E,respectively,based mainly on data from the Tropical Atmosphere and Ocean(TAO)mooring array.We found that turbulent mixing bursts persisted in the thermocline of all three sites.Specifically,the interior turbulent mixing layers(ITMLs)could occur in probability of approximately 68%,53%,and 48%at the three sites,respectively.The overall occurrence probability shows obvious and similar biannual variations at 140°W and 170°W,which is higher in boreal from late summer to winter and lower in spring.Vertically,the ITMLs are primarily located above the EUC core and prevail in deeper(shallower)layers from late summer to winter(spring).Most ITMLs(70%)lasted for hours to 3 days,and a few of them(15%)for more than 7 days.The thicknesses of ITMLs were concentrated between 15 and 55 m.At 165°E,the vertical distribution of ITML occurrence probability was different from that at 140°W and 170°W,as it did not show a preference for depths;the durations of ITMLs are short(also from hours to several days)and their thicknesses were between 5 and 25 m.These properties,particularly the high occurrence probability,and short durations demonstrated the persistence of thermocline mixing in the western to eastern equatorial Pacific thermocline and confirmed the generation mechanism by persistent equatorial waves as well.展开更多
Preparis Channel is the very important exchange path of energy and materials between the northern Bay of Bengal and Andaman Sea(AS).A set of hydrographic measurements,a microstructure profiler,and a deep mooring were ...Preparis Channel is the very important exchange path of energy and materials between the northern Bay of Bengal and Andaman Sea(AS).A set of hydrographic measurements,a microstructure profiler,and a deep mooring were used to determine the characteristics of water masses,turbulent mixing,and flows in the Preparis Channel.The unprecedented short-term mooring data reveal that a deep current in the deep narrow passage(below 400 m)of the Preparis Channel flows toward the Bay of Bengal(BoB)with a mean along-stream velocity of 25.26 cm/s at depth of 540 m;above the deep current,there are a relatively weak current flows toward the AS with a mean along-stream velocity of 15.46 cm/s between 500 m and 520 m,and another weak current flows toward the BoB between 430 m and 500 m.Thus,a sandwiched vertical structure of deep currents(below 400 m)is present in the Preparis Channel.The volume transport below 400 m is 0.06 Sv(1 Sv=106 m^(3)/s)from the AS to the BoB.In the upper layer(shallower than 300 m),the sea water of the AS is relatively warmer and fresher than that in the BoB,indicating a strong exchange through the channel.Microstructure profiler observations reveal that the turbulent diffusivity in the upper layer of the Preparis Channel reaches O(10−4 m^(2)/s),one order larger than that in the interior of the BoB and over the continental slope of the northern AS.We speculate that energetic high-mode internal tides in the Preparis Channel contribute to elevated turbulent mixing.In addition,a local“hotspot”of turbidity is identified at the deep mooring site,at depth of about 100 m,which corresponds to the location of elevated turbulent mixing in the Preparis Channel.展开更多
In this paper,we present a direct numerical simulation(DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number(Re = 1) in a three-dimensional straight channel flow for the first time,us...In this paper,we present a direct numerical simulation(DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number(Re = 1) in a three-dimensional straight channel flow for the first time,using the Giesekus constitutive model for the fluid.In order to generate and maintain the turbulent fluid motion in the straight channel,a sinusoidal force term is added to the momentum equation,and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field.Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS.The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.展开更多
A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order...A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order of magnitude larger than that in the open ocean at that low latitude. Enhanced eddy diffusivities by strong shears and sharp changes in topography were observed. The strongest eddy diffusivity occurred in the mixed layer, and it reached O(10^-2 m^2/s). Strong stratification in the thermocline inhibited the penetration of surface eddy diffusivities through the thermocline, where the mixing was weakest. Below the thermocline, where the background eddy diffusivity was approximately O(10^-6 m^2/s), the eddy diffusivity increased with depth, and its largest value was O(10^-3 m^2/s).展开更多
Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPo...Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPolzin parameterization and the Thorpe-scale method.The observations revealed a clear asymmetrical spatial pattern of turbulent mixing in the anticyclonic eddy area.Enhanced diffusivity(in the order of 10–3 m2/s)was found at the posterior edge of the anticyclonic mesoscale eddy;on the anterior side,diffusivity was one order of magnitude lower on average.This asymmetrical pattern was highly correlated with the eddy kinetic energy.Higher shear variance on the posterior side,which is conducive to the triggering of shear instability,may be the main mechanism for the elevated diffusivity.In addition,the generation and growth of sub-mesoscale motions that are fed by mesoscale eddies on their posterior side may also promote the occurrence of strong mixing in the studied region.The results of this study help improve our knowledge regarding turbulent mixing in the northern SCS.展开更多
The turbulent mixing in the upwelling region east of Hainan Island in the South China Sea is analyzed based on in situ microstructure observations made in July 2012. During the observation, strong upwelling appears in...The turbulent mixing in the upwelling region east of Hainan Island in the South China Sea is analyzed based on in situ microstructure observations made in July 2012. During the observation, strong upwelling appears in the coastal waters, which are 3℃ cooler than the offshore waters and have a salinity 1.0 greater than that of the offshore waters. The magnitude of the dissipation rate of turbulent kinetic energy ε in the upwelling region is O(10–9 W/kg), which is comparable to the general oceanic dissipation. The inferred eddy diffusivity Kρ is O(10–6 m2/s), which is one order of magnitude lower than that in the open ocean. The values are elevated to Kρ≈O(10–4 m2/s) near the boundaries. Weak mixing in the upwelling region is consistent with weak instability as a result of moderate shears versus strong stratifications by the joint influence of surface heating and upwelling of cold water.The validity of two fine-scale structure mixing parameterization models are tested by comparison with the observed dissipation rates. The results indicate that the model developed by Mac Kinnon and Gregg in 2003 provides relatively better estimates with magnitudes close to the observations. Mixing parameterization models need to be further improved in the coastal upwelling region.展开更多
Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline str...Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline structures are distinct due to geographic features and sea ice distribution,resulting in that turbulent dissipation rates(ε) and turbulent diffusivity(K) are vertically and spatially non-uniform.On the shelf north of Antarctic Peninsula and Philip Ridge,with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m,both ε and K show significantly enhanced values in the order of O(10^(-7))-O(10^(-6)) W/kg and O(10^(-3))-O(10^(-2)) m^2/s respectively,about two or three orders of magnitude higher than those in the open ocean.Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau,where s decreases with depth from O(10^(-8)) to O(10^(-9)) W/kg,while K changes vertically in an inverse direction relative to s from O(10^(-6)) to O(10^(-5)) m^2/s.In the marginal ice zone,K is vertically stable with the order of10^(-4) m^2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer.Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions,our results indicate weak relationship between K and wind stress or tidal kinetic energy.Instead,intensified mixing occurs with large bottom roughness,demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing.In addition,geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing.展开更多
We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010.From them we determined the turbulent mixing(dissipation rateεand...We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010.From them we determined the turbulent mixing(dissipation rateεand diapycnal diffusivityκ),nutrients(phosphate,nitrate,and nitrite),nutrient fluxes,and chlorophyll a in two transects(A and B).Transect A was located in the region where turbulent mixing in the upper 100 m was weak(κ~10-6-10-4 m^(2)/s).Transect B was located in the region where the turbulent mixing in the upper 100 m was strong(κ~10-5-10-3 m^(2)/s)due to the influence of internal waves originating from the Luzon Strait and water intrusion from the Western Pacific.In both transects,there was a thin subsurface chlorophyll maximum layer(SCML)(>0.25 mg/m^(3))nested in the upper 100 m.The observations indicate that the effects of turbulent mixing on the distributions of nutrients and chlorophyll a were different in the two transects.In the transect A with weak turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water.Nutrients were sufficient to support a local SCML phytoplankton population and the SCML remained compact.In the transect B with strong turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water,which scatters the nutrients in the water column and diffuses the SCML.展开更多
Based on field hydrological,microstructural,and shipboard Acoustic Doppler Current Profiler data,we quantified the spatial and temporal variability of turbulent mixing in the near-field Changjiang(Yangtze)River plume....Based on field hydrological,microstructural,and shipboard Acoustic Doppler Current Profiler data,we quantified the spatial and temporal variability of turbulent mixing in the near-field Changjiang(Yangtze)River plume.The surface dissipation rate(ε)changed by three orders of magnitude from near-field(10^-4 W/kg)to far-field(10^-7 W/kg)plumes,indicating a decrease with distance from the river mouth.Below the river plume,εchanged with depth to 10^-8 W/kg,and increased to 10^-6 W/kg at the layer where the Taiwan Warm Current(TWC)intruded.Thus,εin the near-field plume showed three layers:surface layer in the river plume,middle layer,and lower TWC layer.In the river plume,the strongestεand turbulent diffusivity(Kz)were greater than 10^-4 W/kg and 10^-2 m^2/s,respectively,during strong ebb tides.A three-orders-of-magnitude change inεand Kz was observed in the tidal cycle.The depth of the halocline changed with tidal cycles,and stratification(N 2)varied by one order of magnitude.Stratification in the TWC layer followed the distribution of the halocline,which is opposite to the dissipation structure.Tidal currents led to intrusion and turbulent mixing in the TWC layer.During ebb tides,εand Kz were as strong as those measured in the river plume,but did not last as long.The structure of the velocity shear was similar to the dissipation rate in both the river plume and TWC layer,whereas the velocity shear in the TWC layer did not match the stratification structure.In the high dissipation rate area,the gradient Richardson number was smaller than the critical value(Ri g<1/4).The Ri g structure was consistent with shear and dissipation distributions,indicating that turbulent mixing in the near-field plume was controlled by a combination of shear induced by the discharged river flow and tidal current.展开更多
The formation and evolution of aerosol in turbulent flows are ubiquitous in both industrial processes and nature. The intricate interaction of turbulent mixing and aerosol evolution in a canonical turbulent mixing lay...The formation and evolution of aerosol in turbulent flows are ubiquitous in both industrial processes and nature. The intricate interaction of turbulent mixing and aerosol evolution in a canonical turbulent mixing layer was investigated by a direct numerical simulation (DNS) in a recent study (Zhou, K., Attili, A., Alshaarawi, A., and Bisetti, F. Simulation of aerosol nucleation and growth in a turbulent mixing layer. Physics of Fluids, 26, 065106 (2014)). In this work, Monte Carlo (MC) simulation of aerosol evolution is carried out along Lagrangian trajectories obtained in the previous simulation, in order to quantify the error of the moment method used in the previous simulation. Moreover, the particle size distribution (PSD), not available in the previous works, is also investigated. Along a fluid parcel moving through the turbulent flow, temperature and vapor concentration exhibit complex fluctuations, triggering complicate aerosol processes and rendering complex PSD. However, the mean PSD is found to be bi-modal in most of the mixing layer except that a tri-modal distribution is found in the turbulent transition region. The simulated PSDs agree with the experiment observations available in the literature. A different explanation on the formation of such PSDs is provided.展开更多
Fluid mixing is an important phenomenon in many physical applications from supernova explosions to genetic structure formations. In this paper, we overview some theoretical and empirical dynamic mix models, which have...Fluid mixing is an important phenomenon in many physical applications from supernova explosions to genetic structure formations. In this paper, we overview some theoretical and empirical dynamic mix models, which have been developed over the recent decades, in particular, the ensemble-average micro physical mix model, the multifluid interpenetration mix model, the phenomenological and hybrid turbulent mix models, the buoyancy drag mix model, the single fluid turbulence mix model, and the large eddy simulation mix model. The similarities, distinctions, and connections between these models and their applications are discussed.展开更多
Upper ocean responses to the passage of sequential tropical cyclones over the northwestern South China Sea(SCS)in 2011 were investigated using satellite remote sensing data,Argo reanalysis data,and an array of mooring...Upper ocean responses to the passage of sequential tropical cyclones over the northwestern South China Sea(SCS)in 2011 were investigated using satellite remote sensing data,Argo reanalysis data,and an array of mooring data.We found that the sea surface low temperature region lasted for more than 38 days and two phytoplankton blooms occurred after the passage of sequential tropical cyclones.The upper ocean cooling reached 2–5°C with a right-side bias was observed along the typhoon track to about 200 km.The maintenance of low temperature region and the two phytoplankton blooms were mainly driven by upwelling and near-inertial turbulence mixing induced by the sequential tropical cyclones.The fi rst phytoplankton bloom appeared on the 7 th day after the passage of the three tropical cyclones,and the chlorophyll-a(chl-a)concentration increased by 226%,which may be mainly driven by typhoons induced upwelling.The second phytoplankton bloom occurred on the 30 th day,the chl-a concentration increased by 290%.Further analysis suggested that only the typhoons with similar characteristics as Nesat and Nalgae can induce strong near-inertial oscillation(NIO).Strong turbulent mixing associated with the near-inertial baroclinic shear instability lasted for 26 days.The measured mean eddy diff usivity in the upper ocean was above 10-4 m 2/s after typhoon Nesat.Enhancement of the turbulent mixing in the upper ocean helped to transport nutrient-rich cold waters from the deep layer to the euphotic layer,and is a major mechanism for the long-term maintenance of low temperature region as well as the second phytoplankton bloom.展开更多
In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into ...In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters(De) and their aspect ratios(AR) range from 1 to 6.5. Planar particle image velocimetry(PIV) is used to measure the velocity field at the same Reynolds number of Re = 5 × 10^4,where Re = Ue De/ν with Ue being the exit bulk velocity and ν the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core,expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet(AR = 6.5) produces the greatest decay rate of the near-field mean velocity, postpones the position at which the 鈥榓xis-switching鈥檖henomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.展开更多
The shock tube experiments of inclined air/SF6 interface instability under the shock wave with the Mach numbers 1.23 and 1.41 are conducted. The numerical simulation is done with the parallel algorithm and the multi-v...The shock tube experiments of inclined air/SF6 interface instability under the shock wave with the Mach numbers 1.23 and 1.41 are conducted. The numerical simulation is done with the parallel algorithm and the multi-viscous-fluid and turbulence (MVFT) code of the large-eddy simulation (LES). The developing process of the interface accelerated by the shock wave is reproduced by the simulations. The complex wave structures, e.g., the propagation, refraction, and reflection of the shock wave, are clearly revealed in the flows. The simulated evolving images of the interface are consistent with the experimental ones. The simulated width of the turbulent mixing zone (TMZ) and the displacements of the bubble and the spike also agree well with the experimental data. Also, the reliability and effectiveness of the MVFT in simulating the problem of interface instability are validated. The more energies are injected into the TMZ when the shock wave has a larger Mach number. Therefore, the perturbed interface develops faster.展开更多
The purpose of this study is to investigate means of controlling the interior ballistic stability of a bulk-loaded propellant gun(BLPG).Experiments on the interaction of twin combustion gas jets and liquid medium in...The purpose of this study is to investigate means of controlling the interior ballistic stability of a bulk-loaded propellant gun(BLPG).Experiments on the interaction of twin combustion gas jets and liquid medium in a cylindrical stepped-wall combustion chamber are conducted in detail to obtain time series processes of jet expansion,and a numerical simulation under the same working conditions is also conducted to verify the reliability of the numerical method by comparing numerical results and experimental results.From this,numerical simulations on mutual interference and expansion characteristics of multiple combustion gas jets(four,six,and eight jets) in liquid medium are carried out,and the distribution characteristic of pressure,velocity,temperature,and evolutionary processes of Taylor cavities and streamlines of jet flow Held are obtained in detail.The results of numerical simulations show that when different numbers of combustion gas jets expand in liquid medium,there are two different types of vortices in the jet flow field,including corner vortices of liquid phase near the step and backflow vortices of gas phase within Taylor cavities.Because of these two types of vortices,the radial expansion characteristic of the jets is increased,while changing numbers of combustion gas jets can restrain Kelvin-Helmholtz instability to a certain degree in jet expansion processes,which can at last realize the goal of controlling the interior ballistic stability of a BLPG.The optimum method for both suppressing Kelvin-Helmholtz instability and promoting radial expansion of Taylor cavities can be determined by analyzing the change of characteristic parameters in a jet flow field.展开更多
A scale-similarity model of a two-point two-time Lagrangian velocity correlation(LVC) was originally developed for the relative dispersion of tracer particles in isotropic turbulent flows(HE, G. W., JIN, G. D., and ZH...A scale-similarity model of a two-point two-time Lagrangian velocity correlation(LVC) was originally developed for the relative dispersion of tracer particles in isotropic turbulent flows(HE, G. W., JIN, G. D., and ZHAO, X. Scale-similarity model for Lagrangian velocity correlations in isotropic and stationary turbulence. Physical Review E, 80, 066313(2009)). The model can be expressed as a two-point Eulerian space correlation and the dispersion velocity V. The dispersion velocity denotes the rate at which one moving particle departs from another fixed particle. This paper numerically validates the robustness of the scale-similarity model at high Taylor micro-scale Reynolds numbers up to 373, which are much higher than the original values(R_λ = 66, 102). The effect of the Reynolds number on the dispersion velocity in the scale-similarity model is carefully investigated. The results show that the scale-similarity model is more accurate at higher Reynolds numbers because the two-point Lagrangian velocity correlations with different initial spatial separations collapse into a universal form compared with a combination of the initial separation and the temporal separation via the dispersion velocity.Moreover, the dispersion velocity V normalized by the Kolmogorov velocity V_η ≡ η/τ_η in which η and τ_η are the Kolmogorov space and time scales, respectively, scales with the Reynolds number R_λ as V/V_η ∝ R_λ^(1.39) obtained from the numerical data.展开更多
Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytic...Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.展开更多
Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibili...Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibility effect came from the reduced pressure-strain term due to reduced pressure fluctuations. Although better understanding of the compressible turbulence is generally achieved with the increased DNS and experimental research effort, there are still some discrepancies among these recent findings. Analysis of the DNS and experimental data suggests that some of the discrepancies are apparent if the compressible effect is related to the turbulent Mach number, Mt. From the comparison of two classes of compressible flow, homogenous shear flow and inhomogeneous shear flow (mixing layer), we found that the effect of compressibility on both classes of shear flow can be characterized in three categories corresponding to three regions of turbulent Mach numbers: the low-Mr, the moderate-Mr and high-Mr regions. In these three regions the effect of compressibility on the growth rate of the turbulent mixing layer thickness is rather different. A simple approach to the reduced pressure-strain effect may not necessarily reduce the mixing-layer growth rate, and may even cause an increase in the growth rate. The present work develops a new second-moment model for the compressible turbulence through the introduction of some blending functions of Mt to account for the compressibility effects on the flow. The model has been successfully applied to the compressible mixing layers.展开更多
This study, using laboratory experiments and scaling analysis, evaluates the influence of geothermal heating on global oceanic circulation. Upon a well-developed large-scale convective flow, an additional heat flux pe...This study, using laboratory experiments and scaling analysis, evaluates the influence of geothermal heating on global oceanic circulation. Upon a well-developed large-scale convective flow, an additional heat flux perturbation 5F/F is employed. The increments of flow and thermal properties, including eddy diffusivity K7, flow velocity Vand bottom temperature Tb, are found to be independent of the applied heat flux F. Together with the scaling analysis of convective flow at different configurations, where the flow is thermally driven in the relatively low or extremely high turbulent thermal convections or the horizontal convection, the variances of flow properties, 6KT/KTand 6V/V, are found to be close to 0.5% and 0.75% at 5F/F=2%. This means that the small heat flux perturbation plays a negligible role in the global convective flow. However, 6Tb/ATis found to be 1.5% at 8F/F=2%, which would have a significant effect in the local region. The results might provide a clue to understanding the influence of geothermal heating on global oceanic circulation. It is expected that geothermal heating will contribute less than 1% in turbulent mixing and volume flux to global oceanic circulation, so its influence can be negligible in this situation. However, when it comes to the local environment, the influence of geothermal heating cannot be ignored. For example, temperature increases of about 0.5℃ with geothermal heating would have a significant effect on the physical environments within the benthic boundary layer.展开更多
The role of wave breaking(WB) in the ocean dynamics in the Bohai Sea,China under typhoon condition is systematically investigated utilizing a coupled wave-current model.The influences of WB on ocean dynamics and proce...The role of wave breaking(WB) in the ocean dynamics in the Bohai Sea,China under typhoon condition is systematically investigated utilizing a coupled wave-current model.The influences of WB on ocean dynamics and processes(mixing coefficient,temperature,mixed layer depth,and current) during the entire typhoon period(including the pre-typhoon,during-typhoon and after-typhoon stages) are comprehensively detected and discussed.Experimental results show that WB greatly enhances the turbulent mixing at about top 10 m depth under typhoon condition,the increase can be up to 10 times that of the normal weather.At the same time,WB generally strengthens the sea surface cooling by ~1.2°C at the during-typhoon stage,about 3 times that in normal weather.The mixed layer depth,is rapidly increased by ~1.6–3.6 m during typhoon due to WB,particularly,the deepening is stronger in the region from 120.5°E to 121.0°E on account of close to the typhoon eye.In addition,WB renders the current speed more uniformly within the entire depth in the Bohai Sea,the change in speed is ~0.2 m/s,whereas the alternation in current vector is generally opposite to the wind direction except for the typhoon eye region,reflecting that WB has an inhibitory effect on the typhoon-forced current change.The effects of WB on vertical mixing coefficient response to the typhoon rapidly,while the impacts of WB on temperature,and mixed layer depth present hysteretic responses to typhoon.Finally,the mechanisms and distribution characteristics of WB-induced mixing and tidal mixing are compared under typhoon condition.展开更多
基金Supported by the National Natural Science Foundation of China(NSFC)(No.41730534)the Laoshan Laboratory Science and Technology Innovation Program(No.LSKJ 202202502)+1 种基金the NSFC(Nos.41976012,42090044)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB42000000)。
文摘A recent study by Liu et al.(2020)suggested that due to the saturation of equatorially trapped planetary waves with different dynamical types,temporal periods,meridional and baroclinic modes,complex layer structures of vertical velocity shear and hence turbulent mixing could frequently occur in the thermocline of the eastern equatorial Pacific.We investigated the occurrence of the interior turbulent mixing as indicated by shear instabilities,above the Equatorial Undercurrent(EUC)core at three equatorial sites along 140°W,170°W,and 165°E,respectively,based mainly on data from the Tropical Atmosphere and Ocean(TAO)mooring array.We found that turbulent mixing bursts persisted in the thermocline of all three sites.Specifically,the interior turbulent mixing layers(ITMLs)could occur in probability of approximately 68%,53%,and 48%at the three sites,respectively.The overall occurrence probability shows obvious and similar biannual variations at 140°W and 170°W,which is higher in boreal from late summer to winter and lower in spring.Vertically,the ITMLs are primarily located above the EUC core and prevail in deeper(shallower)layers from late summer to winter(spring).Most ITMLs(70%)lasted for hours to 3 days,and a few of them(15%)for more than 7 days.The thicknesses of ITMLs were concentrated between 15 and 55 m.At 165°E,the vertical distribution of ITML occurrence probability was different from that at 140°W and 170°W,as it did not show a preference for depths;the durations of ITMLs are short(also from hours to several days)and their thicknesses were between 5 and 25 m.These properties,particularly the high occurrence probability,and short durations demonstrated the persistence of thermocline mixing in the western to eastern equatorial Pacific thermocline and confirmed the generation mechanism by persistent equatorial waves as well.
基金The Global Change and Air-Sea Interaction II Project under contract Nos GASI-01-EIND-STwin and GASI-04-WLHY-03the Scientific Research Fund of the Second Institute of Oceanography,Ministry of Natural Resources under contract No.JB2106+2 种基金the Global Change and Air-Sea Interaction II Project under contract No.GASI-04-WLHY-01the Leading Talents of Science and Technology Innovation in the Zhejiang Provincial Ten Thousand Talents Program under contract No.2020R52038the Oceanic Sustainability-Based Marine Science and Technology Cooperation in Maritime Silk Road and Island Countries.
文摘Preparis Channel is the very important exchange path of energy and materials between the northern Bay of Bengal and Andaman Sea(AS).A set of hydrographic measurements,a microstructure profiler,and a deep mooring were used to determine the characteristics of water masses,turbulent mixing,and flows in the Preparis Channel.The unprecedented short-term mooring data reveal that a deep current in the deep narrow passage(below 400 m)of the Preparis Channel flows toward the Bay of Bengal(BoB)with a mean along-stream velocity of 25.26 cm/s at depth of 540 m;above the deep current,there are a relatively weak current flows toward the AS with a mean along-stream velocity of 15.46 cm/s between 500 m and 520 m,and another weak current flows toward the BoB between 430 m and 500 m.Thus,a sandwiched vertical structure of deep currents(below 400 m)is present in the Preparis Channel.The volume transport below 400 m is 0.06 Sv(1 Sv=106 m^(3)/s)from the AS to the BoB.In the upper layer(shallower than 300 m),the sea water of the AS is relatively warmer and fresher than that in the BoB,indicating a strong exchange through the channel.Microstructure profiler observations reveal that the turbulent diffusivity in the upper layer of the Preparis Channel reaches O(10−4 m^(2)/s),one order larger than that in the interior of the BoB and over the continental slope of the northern AS.We speculate that energetic high-mode internal tides in the Preparis Channel contribute to elevated turbulent mixing.In addition,a local“hotspot”of turbidity is identified at the deep mooring site,at depth of about 100 m,which corresponds to the location of elevated turbulent mixing in the Preparis Channel.
基金Project supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No. 51121004)the National Natural Science Foundation of China (Grant No. 51076036)+2 种基金the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20112302110020)the Fundamental Research Funds for the Central Universities,China (Grant No. HIT.BRET1.2010008)the Japan Society for the Promotion of Science (JSPS) Research Fellowship
文摘In this paper,we present a direct numerical simulation(DNS) of elastic turbulence of viscoelastic fluid at vanishingly low Reynolds number(Re = 1) in a three-dimensional straight channel flow for the first time,using the Giesekus constitutive model for the fluid.In order to generate and maintain the turbulent fluid motion in the straight channel,a sinusoidal force term is added to the momentum equation,and then the elastic turbulence is numerically realized with an initialized chaotic velocity field and a stretched conformation field.Statistical and structural characteristics of the elastic turbulence therein are analyzed based on the detailed information obtained from the DNS.The fluid mixing enhancement effect of elastic turbulence is also demonstrated for the potential applications of this phenomenon.
基金The "CAS/SAFEA International Partnership Program for Creative Research Teams" of Chinese Academy of Seiences under contract Nos XDA11010202,2013CB430303 and 41376022,41276021 and 41276023
文摘A turbulent microstructure experiment was undertaken at a low latitude of 10°N in the South China Sea in late August 2012. The characteristics of the eddy diffusivity above 650 m were analyzed, which is one order of magnitude larger than that in the open ocean at that low latitude. Enhanced eddy diffusivities by strong shears and sharp changes in topography were observed. The strongest eddy diffusivity occurred in the mixed layer, and it reached O(10^-2 m^2/s). Strong stratification in the thermocline inhibited the penetration of surface eddy diffusivities through the thermocline, where the mixing was weakest. Below the thermocline, where the background eddy diffusivity was approximately O(10^-6 m^2/s), the eddy diffusivity increased with depth, and its largest value was O(10^-3 m^2/s).
基金The National Key R&D Plan of China under contract Nos 2017YFC0305904,2017YFC0305804 and 2016YFC1401404the National Natural Science Foundation of China under contract Nos 41876023,41630970,41806037,41706137 and 41806033+4 种基金the Guangdong Science and Technology Project under contract Nos 2019A1515111044,2018A0303130047 and 2017A030310332the Guangzhou Science and Technology Project under contract No.201707020037the Natural Science Foundation of Shenzhen University under contract No.2019078the Dedicated Fund for Promoting High-quality Economic Development in Guangdong Province(Marine Economic Development Project)under contract No.GDOE2019A03the Independent Research Project Program of State Key Laboratory of Tropical Oceanography under contract Nos LTOZZ1902 and LTO1909。
文摘Upper turbulent mixing in the interior and surrounding areas of an anticyclonic eddy in the northern South China Sea(SCS)was estimated from underwater glider data(May 2015)in the present study,using the Gregg-HenyeyPolzin parameterization and the Thorpe-scale method.The observations revealed a clear asymmetrical spatial pattern of turbulent mixing in the anticyclonic eddy area.Enhanced diffusivity(in the order of 10–3 m2/s)was found at the posterior edge of the anticyclonic mesoscale eddy;on the anterior side,diffusivity was one order of magnitude lower on average.This asymmetrical pattern was highly correlated with the eddy kinetic energy.Higher shear variance on the posterior side,which is conducive to the triggering of shear instability,may be the main mechanism for the elevated diffusivity.In addition,the generation and growth of sub-mesoscale motions that are fed by mesoscale eddies on their posterior side may also promote the occurrence of strong mixing in the studied region.The results of this study help improve our knowledge regarding turbulent mixing in the northern SCS.
基金The National Natural Science Foundation of China under contract Nos 41476009,41776034 and 41476010the Natural Science Foundation of Guangdong Province of China under contract No.2016A030312004+1 种基金the Global Air-Sea Interaction Project of State Oceanic Administration under contract No.GASI-IPOVAI-01-02the Laboratory of Tropical Ocean Open Foundation under contract No.LT1404
文摘The turbulent mixing in the upwelling region east of Hainan Island in the South China Sea is analyzed based on in situ microstructure observations made in July 2012. During the observation, strong upwelling appears in the coastal waters, which are 3℃ cooler than the offshore waters and have a salinity 1.0 greater than that of the offshore waters. The magnitude of the dissipation rate of turbulent kinetic energy ε in the upwelling region is O(10–9 W/kg), which is comparable to the general oceanic dissipation. The inferred eddy diffusivity Kρ is O(10–6 m2/s), which is one order of magnitude lower than that in the open ocean. The values are elevated to Kρ≈O(10–4 m2/s) near the boundaries. Weak mixing in the upwelling region is consistent with weak instability as a result of moderate shears versus strong stratifications by the joint influence of surface heating and upwelling of cold water.The validity of two fine-scale structure mixing parameterization models are tested by comparison with the observed dissipation rates. The results indicate that the model developed by Mac Kinnon and Gregg in 2003 provides relatively better estimates with magnitudes close to the observations. Mixing parameterization models need to be further improved in the coastal upwelling region.
基金Chinese Polar Environment Comprehensive Investigation and Assessment Programs under contract Nos CHINARE-01-01and CHINARE-04-01
文摘Turbulent mixing in the upper ocean(30-200 m) of the northwestern Weddell Sea is investigated based on profiles of temperature,salinity and microstructure data obtained during February 2014.Vertical thermohaline structures are distinct due to geographic features and sea ice distribution,resulting in that turbulent dissipation rates(ε) and turbulent diffusivity(K) are vertically and spatially non-uniform.On the shelf north of Antarctic Peninsula and Philip Ridge,with a relatively homogeneous vertical structure of temperature and salinity through the entire water column in the upper 200 m,both ε and K show significantly enhanced values in the order of O(10^(-7))-O(10^(-6)) W/kg and O(10^(-3))-O(10^(-2)) m^2/s respectively,about two or three orders of magnitude higher than those in the open ocean.Mixing intensities tend to be mild due to strong stratification in the Powell Basin and South Orkney Plateau,where s decreases with depth from O(10^(-8)) to O(10^(-9)) W/kg,while K changes vertically in an inverse direction relative to s from O(10^(-6)) to O(10^(-5)) m^2/s.In the marginal ice zone,K is vertically stable with the order of10^(-4) m^2/s although both intense dissipation and strong stratification occur at depth of 50-100 m below a cold freshened mixed layer.Though previous studies indentify wind work and tides as the primary energy sources for turbulent mixing in coastal regions,our results indicate weak relationship between K and wind stress or tidal kinetic energy.Instead,intensified mixing occurs with large bottom roughness,demonstrating that only when internal waves generated by wind and tide impinge on steep topography can the energy dissipate to support mixing.In addition,geostrophic current flowing out of the Weddell Sea through the gap west of Philip Passage is another energy source contributing to the local intense mixing.
基金Supported by the National Key R&D Program of China(No.2018YFA0902500)the National Natural Science Foundation of China(Nos.41706137,41806033,41876023)+5 种基金the Natural Science Foundation of Guangdong Province of China(No.2017A030310332)the State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences(No.LTO1909)the Natural Science Foundation of SZU(Nos.2019078,860-000002110258)the Dedicated Fund for Promoting High-quality Economic Development in Guangdong Province(Marine Economic Development Project)(No.GDOE[2019]A03)the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2019ZD0304)the Independent Research Project Program of State Key Laboratory of Tropical Oceanography(No.LTOZZ1902)。
文摘We present observations from deployments of turbulent microstructure instrument and CTD package in the northern South China Sea from April to May 2010.From them we determined the turbulent mixing(dissipation rateεand diapycnal diffusivityκ),nutrients(phosphate,nitrate,and nitrite),nutrient fluxes,and chlorophyll a in two transects(A and B).Transect A was located in the region where turbulent mixing in the upper 100 m was weak(κ~10-6-10-4 m^(2)/s).Transect B was located in the region where the turbulent mixing in the upper 100 m was strong(κ~10-5-10-3 m^(2)/s)due to the influence of internal waves originating from the Luzon Strait and water intrusion from the Western Pacific.In both transects,there was a thin subsurface chlorophyll maximum layer(SCML)(>0.25 mg/m^(3))nested in the upper 100 m.The observations indicate that the effects of turbulent mixing on the distributions of nutrients and chlorophyll a were different in the two transects.In the transect A with weak turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water.Nutrients were sufficient to support a local SCML phytoplankton population and the SCML remained compact.In the transect B with strong turbulent mixing,nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water,which scatters the nutrients in the water column and diffuses the SCML.
基金the National Natural Science Foundation of China(NSFC)(No.41706012)the National Key Research and Development Program of China(No.2017YFC1403401)+1 种基金the National Natural Science Foundation of China(NSFC)Innovative Group Grant(No.41421005),the NSFC-Shandong Joint Fund for Marine Science Research Centers(No.U1406401)the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDA11020301)。
文摘Based on field hydrological,microstructural,and shipboard Acoustic Doppler Current Profiler data,we quantified the spatial and temporal variability of turbulent mixing in the near-field Changjiang(Yangtze)River plume.The surface dissipation rate(ε)changed by three orders of magnitude from near-field(10^-4 W/kg)to far-field(10^-7 W/kg)plumes,indicating a decrease with distance from the river mouth.Below the river plume,εchanged with depth to 10^-8 W/kg,and increased to 10^-6 W/kg at the layer where the Taiwan Warm Current(TWC)intruded.Thus,εin the near-field plume showed three layers:surface layer in the river plume,middle layer,and lower TWC layer.In the river plume,the strongestεand turbulent diffusivity(Kz)were greater than 10^-4 W/kg and 10^-2 m^2/s,respectively,during strong ebb tides.A three-orders-of-magnitude change inεand Kz was observed in the tidal cycle.The depth of the halocline changed with tidal cycles,and stratification(N 2)varied by one order of magnitude.Stratification in the TWC layer followed the distribution of the halocline,which is opposite to the dissipation structure.Tidal currents led to intrusion and turbulent mixing in the TWC layer.During ebb tides,εand Kz were as strong as those measured in the river plume,but did not last as long.The structure of the velocity shear was similar to the dissipation rate in both the river plume and TWC layer,whereas the velocity shear in the TWC layer did not match the stratification structure.In the high dissipation rate area,the gradient Richardson number was smaller than the critical value(Ri g<1/4).The Ri g structure was consistent with shear and dissipation distributions,indicating that turbulent mixing in the near-field plume was controlled by a combination of shear induced by the discharged river flow and tidal current.
基金Project supported by the National Natural Science Foundation of China(Nos.11402179 and11572274)
文摘The formation and evolution of aerosol in turbulent flows are ubiquitous in both industrial processes and nature. The intricate interaction of turbulent mixing and aerosol evolution in a canonical turbulent mixing layer was investigated by a direct numerical simulation (DNS) in a recent study (Zhou, K., Attili, A., Alshaarawi, A., and Bisetti, F. Simulation of aerosol nucleation and growth in a turbulent mixing layer. Physics of Fluids, 26, 065106 (2014)). In this work, Monte Carlo (MC) simulation of aerosol evolution is carried out along Lagrangian trajectories obtained in the previous simulation, in order to quantify the error of the moment method used in the previous simulation. Moreover, the particle size distribution (PSD), not available in the previous works, is also investigated. Along a fluid parcel moving through the turbulent flow, temperature and vapor concentration exhibit complex fluctuations, triggering complicate aerosol processes and rendering complex PSD. However, the mean PSD is found to be bi-modal in most of the mixing layer except that a tri-modal distribution is found in the turbulent transition region. The simulated PSDs agree with the experiment observations available in the literature. A different explanation on the formation of such PSDs is provided.
基金performed under the auspices of the U.S. Department of Energyby the Los Alamos National Laboratory under contract number W-7405-ENG-36
文摘Fluid mixing is an important phenomenon in many physical applications from supernova explosions to genetic structure formations. In this paper, we overview some theoretical and empirical dynamic mix models, which have been developed over the recent decades, in particular, the ensemble-average micro physical mix model, the multifluid interpenetration mix model, the phenomenological and hybrid turbulent mix models, the buoyancy drag mix model, the single fluid turbulence mix model, and the large eddy simulation mix model. The similarities, distinctions, and connections between these models and their applications are discussed.
基金Supported by the Basic Project of the Ministry of Science and Technology(No.2016YFC14001403)the National Program on Global Change and Air-Sea Interaction(No.GASI-IPOVAI-04)+1 种基金the National Science Foundation of China(Nos.41676008,40876005,U1901213)the Scientifi c Research Start-Up Foundation of Shantou University(No.NTF20006)。
文摘Upper ocean responses to the passage of sequential tropical cyclones over the northwestern South China Sea(SCS)in 2011 were investigated using satellite remote sensing data,Argo reanalysis data,and an array of mooring data.We found that the sea surface low temperature region lasted for more than 38 days and two phytoplankton blooms occurred after the passage of sequential tropical cyclones.The upper ocean cooling reached 2–5°C with a right-side bias was observed along the typhoon track to about 200 km.The maintenance of low temperature region and the two phytoplankton blooms were mainly driven by upwelling and near-inertial turbulence mixing induced by the sequential tropical cyclones.The fi rst phytoplankton bloom appeared on the 7 th day after the passage of the three tropical cyclones,and the chlorophyll-a(chl-a)concentration increased by 226%,which may be mainly driven by typhoons induced upwelling.The second phytoplankton bloom occurred on the 30 th day,the chl-a concentration increased by 290%.Further analysis suggested that only the typhoons with similar characteristics as Nesat and Nalgae can induce strong near-inertial oscillation(NIO).Strong turbulent mixing associated with the near-inertial baroclinic shear instability lasted for 26 days.The measured mean eddy diff usivity in the upper ocean was above 10-4 m 2/s after typhoon Nesat.Enhancement of the turbulent mixing in the upper ocean helped to transport nutrient-rich cold waters from the deep layer to the euphotic layer,and is a major mechanism for the long-term maintenance of low temperature region as well as the second phytoplankton bloom.
基金Project supported by the Fundamental Research Funds for the Central Universities,China(Grant No.3132014050)the General Science Research Project of the Education Department of Liaoning Province,China(Grant No.L2013198)+1 种基金the Natural Science Foundation of Liaoning Province,China(Grant No.L2014025012)the National Natural Science Foundation of China(Grant Nos.10921202 and 11072005)
文摘In this paper, we experimentally investigate the near-field flow characteristics of turbulent free jets respectively issued from circular, triangular, diamond, rectangular, and notched-rectangular orifice plates into air surroundings. All the orifice plates have identical opening areas or equivalent diameters(De) and their aspect ratios(AR) range from 1 to 6.5. Planar particle image velocimetry(PIV) is used to measure the velocity field at the same Reynolds number of Re = 5 × 10^4,where Re = Ue De/ν with Ue being the exit bulk velocity and ν the kinematic viscosity of fluid. The mean and turbulent velocity fields of all the five jets are compared in detail. Results show that the noncircular jets can enhance the entrainment rate, reflected by the higher acceleration rates of mean velocity decay and spread, shorten the length of the unmixed core,expedite the increase of turbulent intensity compared with the circular counterpart shortened unmixed core, and increase turbulent intensity comparing to the circular counterpart. Among the five jets, the rectangular jet(AR = 6.5) produces the greatest decay rate of the near-field mean velocity, postpones the position at which the 鈥榓xis-switching鈥檖henomenon occurs. This supports that axis switching phenomenon strongly depends on jet initial conditions. In addition, the hump in the centerline variation of the turbulence intensity is observed in the rectangular and triangular jets, but not in the circular jet, nor in diamond jet nor in notched-rectangular jet.
基金supported by the National Natural Science Foundation of China (Nos. 11072228 and 11002129)
文摘The shock tube experiments of inclined air/SF6 interface instability under the shock wave with the Mach numbers 1.23 and 1.41 are conducted. The numerical simulation is done with the parallel algorithm and the multi-viscous-fluid and turbulence (MVFT) code of the large-eddy simulation (LES). The developing process of the interface accelerated by the shock wave is reproduced by the simulations. The complex wave structures, e.g., the propagation, refraction, and reflection of the shock wave, are clearly revealed in the flows. The simulated evolving images of the interface are consistent with the experimental ones. The simulated width of the turbulent mixing zone (TMZ) and the displacements of the bubble and the spike also agree well with the experimental data. Also, the reliability and effectiveness of the MVFT in simulating the problem of interface instability are validated. The more energies are injected into the TMZ when the shock wave has a larger Mach number. Therefore, the perturbed interface develops faster.
基金supported by National Natural Science Foundation of China(Grant 11372139)
文摘The purpose of this study is to investigate means of controlling the interior ballistic stability of a bulk-loaded propellant gun(BLPG).Experiments on the interaction of twin combustion gas jets and liquid medium in a cylindrical stepped-wall combustion chamber are conducted in detail to obtain time series processes of jet expansion,and a numerical simulation under the same working conditions is also conducted to verify the reliability of the numerical method by comparing numerical results and experimental results.From this,numerical simulations on mutual interference and expansion characteristics of multiple combustion gas jets(four,six,and eight jets) in liquid medium are carried out,and the distribution characteristic of pressure,velocity,temperature,and evolutionary processes of Taylor cavities and streamlines of jet flow Held are obtained in detail.The results of numerical simulations show that when different numbers of combustion gas jets expand in liquid medium,there are two different types of vortices in the jet flow field,including corner vortices of liquid phase near the step and backflow vortices of gas phase within Taylor cavities.Because of these two types of vortices,the radial expansion characteristic of the jets is increased,while changing numbers of combustion gas jets can restrain Kelvin-Helmholtz instability to a certain degree in jet expansion processes,which can at last realize the goal of controlling the interior ballistic stability of a BLPG.The optimum method for both suppressing Kelvin-Helmholtz instability and promoting radial expansion of Taylor cavities can be determined by analyzing the change of characteristic parameters in a jet flow field.
基金Project supported by the Science Challenge Program(No.TZ2016001)the National Natural Science Foundation of China(Nos.11472277,11572331,11232011,and 11772337)+1 种基金the Strategic Priority Research Program,Chinese Academy of Sciences(No.XDB22040104)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(No.QYZDJ-SSW-SYS002)
文摘A scale-similarity model of a two-point two-time Lagrangian velocity correlation(LVC) was originally developed for the relative dispersion of tracer particles in isotropic turbulent flows(HE, G. W., JIN, G. D., and ZHAO, X. Scale-similarity model for Lagrangian velocity correlations in isotropic and stationary turbulence. Physical Review E, 80, 066313(2009)). The model can be expressed as a two-point Eulerian space correlation and the dispersion velocity V. The dispersion velocity denotes the rate at which one moving particle departs from another fixed particle. This paper numerically validates the robustness of the scale-similarity model at high Taylor micro-scale Reynolds numbers up to 373, which are much higher than the original values(R_λ = 66, 102). The effect of the Reynolds number on the dispersion velocity in the scale-similarity model is carefully investigated. The results show that the scale-similarity model is more accurate at higher Reynolds numbers because the two-point Lagrangian velocity correlations with different initial spatial separations collapse into a universal form compared with a combination of the initial separation and the temporal separation via the dispersion velocity.Moreover, the dispersion velocity V normalized by the Kolmogorov velocity V_η ≡ η/τ_η in which η and τ_η are the Kolmogorov space and time scales, respectively, scales with the Reynolds number R_λ as V/V_η ∝ R_λ^(1.39) obtained from the numerical data.
文摘Natural beaches tend to be concave-up rather than planar and are reasonable to be modeled by an equilibrium beach profile. A governing equation for longshore current on an equilibrium beach is derived and its analytical solution is given in this paper. Through comparisons of the present solution and field data of longshore current for a step-type beach, the present solution is found to have fairly agreeable prediction to longshore current inside the surf zone. The effects of the shape of a concave-up beach and turbulent mixing stress on longshore current inside the surf zone are discussed in the present paper.
基金the National Natural Science Foundation of China (10232020,90505005)
文摘Previous studies carried out in the early 1990s conjectured that the main compressible effects could be associated with the dilatational effects of velocity fluctuation. Later, it was shown that the main compressibility effect came from the reduced pressure-strain term due to reduced pressure fluctuations. Although better understanding of the compressible turbulence is generally achieved with the increased DNS and experimental research effort, there are still some discrepancies among these recent findings. Analysis of the DNS and experimental data suggests that some of the discrepancies are apparent if the compressible effect is related to the turbulent Mach number, Mt. From the comparison of two classes of compressible flow, homogenous shear flow and inhomogeneous shear flow (mixing layer), we found that the effect of compressibility on both classes of shear flow can be characterized in three categories corresponding to three regions of turbulent Mach numbers: the low-Mr, the moderate-Mr and high-Mr regions. In these three regions the effect of compressibility on the growth rate of the turbulent mixing layer thickness is rather different. A simple approach to the reduced pressure-strain effect may not necessarily reduce the mixing-layer growth rate, and may even cause an increase in the growth rate. The present work develops a new second-moment model for the compressible turbulence through the introduction of some blending functions of Mt to account for the compressibility effects on the flow. The model has been successfully applied to the compressible mixing layers.
基金The National Natural Science Foundation(NSF)of China under contract Nos 41176027 and 11072253the Strategic Priority Research Program of the Chinese Academy of Sciences under contract No.XDA11030302the State Key Laboratory of Tropical Oceanography(LTO)grant,South China Sea Institute of Oceanography,Chinese Academy of Sciences,under contract No.LTOZZ1304
文摘This study, using laboratory experiments and scaling analysis, evaluates the influence of geothermal heating on global oceanic circulation. Upon a well-developed large-scale convective flow, an additional heat flux perturbation 5F/F is employed. The increments of flow and thermal properties, including eddy diffusivity K7, flow velocity Vand bottom temperature Tb, are found to be independent of the applied heat flux F. Together with the scaling analysis of convective flow at different configurations, where the flow is thermally driven in the relatively low or extremely high turbulent thermal convections or the horizontal convection, the variances of flow properties, 6KT/KTand 6V/V, are found to be close to 0.5% and 0.75% at 5F/F=2%. This means that the small heat flux perturbation plays a negligible role in the global convective flow. However, 6Tb/ATis found to be 1.5% at 8F/F=2%, which would have a significant effect in the local region. The results might provide a clue to understanding the influence of geothermal heating on global oceanic circulation. It is expected that geothermal heating will contribute less than 1% in turbulent mixing and volume flux to global oceanic circulation, so its influence can be negligible in this situation. However, when it comes to the local environment, the influence of geothermal heating cannot be ignored. For example, temperature increases of about 0.5℃ with geothermal heating would have a significant effect on the physical environments within the benthic boundary layer.
基金The Grant from Guangxi Key Laboratory of Marine Environment Change and Disaster in Beibu Gulf under contract No.2021KF03the National Natural Science Foundation of China under contract Nos 42176020 and 42076007+1 种基金the Foundation from Key Laboratory of Marine Environmental Information Technology,Ministry of Natural Resources of China under contract No.2020GKF-0812the Tianjin Natural Science Foundation under contract No.18JCYBJC84900。
文摘The role of wave breaking(WB) in the ocean dynamics in the Bohai Sea,China under typhoon condition is systematically investigated utilizing a coupled wave-current model.The influences of WB on ocean dynamics and processes(mixing coefficient,temperature,mixed layer depth,and current) during the entire typhoon period(including the pre-typhoon,during-typhoon and after-typhoon stages) are comprehensively detected and discussed.Experimental results show that WB greatly enhances the turbulent mixing at about top 10 m depth under typhoon condition,the increase can be up to 10 times that of the normal weather.At the same time,WB generally strengthens the sea surface cooling by ~1.2°C at the during-typhoon stage,about 3 times that in normal weather.The mixed layer depth,is rapidly increased by ~1.6–3.6 m during typhoon due to WB,particularly,the deepening is stronger in the region from 120.5°E to 121.0°E on account of close to the typhoon eye.In addition,WB renders the current speed more uniformly within the entire depth in the Bohai Sea,the change in speed is ~0.2 m/s,whereas the alternation in current vector is generally opposite to the wind direction except for the typhoon eye region,reflecting that WB has an inhibitory effect on the typhoon-forced current change.The effects of WB on vertical mixing coefficient response to the typhoon rapidly,while the impacts of WB on temperature,and mixed layer depth present hysteretic responses to typhoon.Finally,the mechanisms and distribution characteristics of WB-induced mixing and tidal mixing are compared under typhoon condition.