Vertical multiple-layer structure of temperature and turbulent diffusivity in the South China Sea

We report field measurements of vertical profiles of the turbulent diffusivity and temperature at different stations in the South China Sea(SCS).Our study shows that the measured turbulent diffusivity follows a power-law distribution with a varying exponent in water layers.Similar multiple-layer scaling regimes were also observed from the temperature fluctuations.Combining turbulent diffusivity and temperature fluctuations,the vertical structure of temperature was revealed.Furthermore,we discussed the temperature profiles in each layer.A constant function of a dimensionless temperature profile was found in water layers that have identical turbulence conditions.Our results reveal the multiple-layer structure of temperature in the SCS.This study contributes to the understanding of the vertical structure of multiple layers in the SCS and provides clues for exploring the physical mechanism for maintaining the temperature structure.

Turbulence and Fossil Turbulence in Oceans and Lakes

Turbulence is defined as an eddy-like state of fluid motion where the inertial-vortex forces of the eddies are larger than any of the other forces that tend to damp the eddies out. Energy cascades of irrotational flows from large scales to small are non-turbulent, even if they supply energy to turbulence. Turbulent flows are rotational and cascade from small scales to large, with feedback. Viscous forces limit the smallest turbulent eddy size to the Kolmogorov scale. In stratified fluids, buoyancy forces limit large vertical overturns to the Ozmidov scale and convert the largest turbulent eddies into a unique class of saturated, non-propagating, internal waves, termed fossil-vorticity-turbulence. These waves have the same energy but different properties and spectral forms than the original turbulence patch. The Gibson (1980, 1986) theory of fossil turbulence applies universal similarity theories of turbulence and turbulent mixing to the vertical evolution of an isolated patch of turbulence in a stratified fluid as its growth is constrained and fossilized by buoyancy forces. Quantitative hydrodynamic-phase-diagrams (HPDs) from the theory are used to classify microstructure patches according to their hydrodynamic states. When analyzed in HPD space, previously published oceanic datasets showed their dominant microstructure patches are fossilized at large scales in all layers. Laboratory and field measurements suggested phytoplankton species with different swimming abilities adjust their growth strategies by pattern recognition of turbulence-fossil-turbulence dissipation and persistence times that predict survival-relevant surface layer sea changes. New data collected near a Honolulu waste-water outfall showed the small-to-large evolution of oceanic turbulence microstructure from active to fossil states, and revealed the ability of fossil-density-turbulence patches to absorb, and vertically radiate, internal wave energy, information, and enhanced turbulent-mixing-rates toward the sea surface so that the submerged waste-field could be detected from a space satellite (Bondur and Filatov, 2003).

Positive and negative turbulent heat diffusivity observed on a 325-m meteorological tower in Beijing

Turbulent diffusion efficiently transports momentum,heat,and matter and affects their transfers between the atmosphere and the surface.As a key parameter in describing turbulent diffusion,the turbulent heat diffusivity KH has rarely been studied in the context of frequent urban pollution in recent years.In this study,KH under urban pollution conditions was directly calculated based on K-theory.The authors found an obvious diurnal variation in K_(H),with variations also in the vertical distributions between each case and over time.Interestingly,the height corresponding to the high occurrence frequency of negative K_(H) rises gradually after sunrise,peaks at noon,falls near sunset,and concentrates around 140 m during most of the night.The KH magnitude and fluctuation are smaller in the pollutant accumulation stage(CS)at all levels than in the pollutant transport stage and pollutant removal stage.Turbulent diffusion may greatly affect PM_(2.5) concentrations at the CS because of the negative correlation between PM_(2.5) concentrations and the absolute value of KH at the CS accompanied by weak wind speeds.The applicability of K-theory is not very good during either day or at night.These problems are inherent in K-theory when characterizing complex systems,such as turbulent diffusion,and require new frameworks or parameterization schemes.These findings may provide valuable insight for establishing a new turbulence diffusion parameterization scheme for KH and promote the study of turbulent diffusion,air quality forecasting,and weather and climate modeling.

A turbulent mass diffusivity model for analyzing the mixing characteristics in an impinging stream-rotating packed bed

In this study,the fluid flow and mixing process in an impinging stream-rotating packed bed(IS-RPB)is simulated by using a new three-dimensional computational fluid dynamics model.Specifically,the gaseliquid flow is simulated by the Euler-Euler model,the hydrodynamics of the reactor is predicted by the RNG k-εmethod,and the high-gravity environment is simulated by the sliding mesh model.The turbulent mass transfer process is characterized by the concentration variance c^(2) and its dissipation rateεc formulations,and therefore the turbulent mass diffusivity can be directly obtained.The simulated segregation index Xs is in agreement with our previous experimental results.The simulated results reveal that the fringe effect of IS can be offset by the end effect at the inner radius of RPB,so the investigation of the coupling mechanism between IS and RPB is critical to intensify the mixing process in IS-RPB.

Numerical Simulation of Water Exchange Characteristics of the Jiaozhou Bay Based on A Three-Dimensional Lagrangian Model

Based on theory of three-dimensional hydrodynamics, an Euler-Lagrangian particle model is established to study the transport and water exchange capability in the Jiaozhou Bay. The three-dimensional hydrodynamic model, driven by tide and wind, is used to study the effects of wetting and drying of estuarine intertidal flats by the dry-wet grid technology based on the Estuarine, Coastal and Ocean Model （ECOM）. The particle model includes the advection and the diffusion processes, of which the advection process is simulated with a certain method, and the diffusion process is simulated with the random walk method. The effect of the intertidal zone, the turbulent diffusion and the timescales of the water exchange are also discussed. The results show that a moving boundary model can simulate the transport process of the particle in the intertidal zone, where the particles are transported for a longer distance than that of the stationary result. Simulations with and without the turbulent random walk show that the effect of turbulent diffusion is very effective at spreading particles throughout the estuary and speeding up the particle movement. The spatial distribution of residence time is given to quantify the water exchange capability that has very important ramifications to water quality. The effect of wind on the water exchange is also examined and the southeasterly wind in summer tends to block the water exchange near the northeast coast, while the northerly wind in winter speeds up the transport process. These results indicate that the Lagrangian particle model is applicable and has a large potential to help understanding the water exchange capability in estuaries, which can also be useful to simulate the transport process of contaminant.

Physical oceanography of the Caroline M4 seamount in the tropical Western Pacific Ocean in summer 2017

Physical oceanography plays an important role in the formation of submarine sediments,and the distribution of nutriments and biocenoses in seamounts.The M4 seamount is located in the Caroline Island Ridge of the Western Pacific Ocean.The physical properties around M4 seamount are preliminarily analyzed based on the in-situ data obtained in summer 2017 in Caroline M4 seamount and open-sourced data.We found that the water in the upper 200 m is controlled by the westward North Equatorial Current(NEC),while the water between 300-1000 m is dominated by the eastward North Equatorial Undercurrent(NEUC).The current direction fluctuates significantly below 300 m at upstream stations.At the same depth of the lee sides,the current direction changes with the distance from seamount.These are likely caused by the obstacle of M4 seamount.The calculation results show that there is an anticyclonic cap above M4 seamount caused by tidal rectification.Tidal currents in M4 seamount are squeezed by the topography and amplified,and the amplified tidal currents play a dominant role in M4 seamount.First,the circulation system generated by the interaction of the amplified tidal current and M4 seamount drives the upward/downward movement of the isotherms.Secondly,the thickness of the surface turbulent layer is changed with the tidal phase.Thirdly,high turbulent diffusivities are found in the bottom of M4 seamount,and these are most likely attributed to the turbulent mixing induced by the mutual effect between semidiurnal tidal currents and steep bathymetry.This article of physical oceanography provides scientific basis for further analysis of the distribution of biological community and deposition mechanism in M4 seamount.

Computational Mass Transfer Method for Chemical Process Simulation

The recent works on the development of computational mass transfer （CMT） method and its applications in chemical process simulation are reviewed. Some development strategies and challenges in future research are also discussed.

Mathematical Model of Combustion in Blunt Annular Ceramic Burner

The computer simulation of the combustion process in blast furnace(BF) stove has been studied by using the k-ε-g turbulent diffusion flame model.The combustion process in blunt annular ceramic burner was calculated by using the software.The profiles of gas and air velocity,temperature of the combustion products,concentration of the components,and the shape and length of the flame during combustion have been researched.Compared with the original annular ceramic burner,the new design of the blunt one improves the mixing of the gas and the air significantly,and shortened the length of the flame.

Prediction of Distillation Column Performance by Computational Mass Transfer Method

A computational mass transfer model is proposed for predicting the concentration profile and Murphree efficiency of sieve tray distillation column. The proposed model is based on using modified c＇2 -εc＇ two equations formulation for closing the differential turbulent mass transfer equation with improvement by considering the vapor injected from the sieve hole to be three dimensional. The predicted concentration distributions by using proposed model were checked by experimental work conducted on a sieve tray simulator of 1.2 meters in diameter for desorbing the dissolved oxygen in the feed water by blowing air. The model predictions were confirmed by the experimental measurement. The validation of the proposed model was further tested by comparing the simulated result with the performance of an industrial scale sieve tray distillation column reported by Kunesh et al. for the stripping of toluene from its water solution. The predicted outlet concentration of each tray and the Murphree tray efficiencies under different operating conditions were in agreement with the published data. The simulated turbulent mass transfer diffusivity on each tray was within the range of the experimental result in the same sieve column reported by Cai et al. In addition, the prediction of the influence of sieve tray structure on the tray efficiency by using the proposed model was demonstrated.

Observation of physical oceanography at the Y3 seamount (Yap Arc) in winter 2014

Seamounts aff ect the surrounding physical oceanography and form unique dynamic processes.The infl uences of these processes on biological and sedimentary distributions are quite diff erent in seamount areas at diff erent depths.The Y3 seamount is located in the Yap Arc of the tropical Western Pacifi c Ocean.The water depth of its summit is~280 m.Based on fi eld data obtained in December 2014 and other open-access data,the physical oceanography around the Y3 seamount was preliminarily analyzed.The results show that the upper layer(0-150 m)was under the infl uence of the westward-fl owing North Equatorial Current(NEC),while the eastward-fl owing North Equatorial Undercurrent(NEUC)controlled the water between 200-800 m.The NEC was strong and steady,but the NEUC was disturbed by the Y3 seamount.The cold dome above the Y3 seamount was not caused by a Taylor cap or tidal rectifi cation but probably by upwelling during the survey time.Tidal currents were squeezed against topography and greatly amplifi ed in the Y3 seamount.The thicknesses of the surface turbulent layers were greatly infl uenced by the spring-neap tidal cycle.The turbulent diff usivities in the sea surface layer above the Y3 seamount were much larger than those in the open ocean.Calculations showed that the surface wind stress greatly aff ected the turbulent mixing in the surface layer of the Y3 seamount.The reciprocal action between the amplifi ed tidal currents and topography was the most likely cause of the turbulent mixing near the bottom of the Y3 seamount.This study can provide a scientifi c basis for further study of biological and depositional characteristics at the Y3 seamount.

Application of WSGSA Model in Predicting Temperature and Soot in C_(2)H_(4)/Air Turbulent Diffusion Flame

Soot,a product of insufficient combustion,is usually in the form of aggregate. The multi-scattering of soot fractal aggregates has been proved to play an important role in studying the soot radiative properties,which is rarely considered in predicting the radiative heat transfer in combustion flame. In the present study,based on the weighted sum of gray soot fractal aggregate(WSGSA) model,which is used to predict the temperature field and soot aggregates in turbulent diffusion flame,the flame temperature distribution and soot volume fraction distribution under the conditions of the model without considering radiation,the default radiation model in Fluent software and the WSGSA model are calculated respectively. The results show that the flame temperature will be seriously overestimated without considering radiation and the maximum relative discrepancy of flame centerline temperature is about 64.5%. The accuracy will be improved by the default radiation model in the Fluent software,but the flame temperature is still overestimated and the maximum relative discrepancy of flame centerline temperature is about 42.1%. However,more satisfactory results can be obtained by the WSGSA model,and the maximum relative discrepancy of flame centerline temperature is no more than 15.3%. Similar conclusions can also be obtained in studying the temperature distribution along different flame heights. Moreover,the soot volume fraction can be predicted more accurately with the application of the WSGSA model. Both without considering radiation and using the default radiation model in the Fluent software will result in the underestimating of soot volume fraction. All the results reveal that the WSGSA model can be used to predict the temperature and soot aggregates in the CH/air turbulent diffusion flame.

A Reynolds mass flux model for gas separation process simulation:Ⅱ.Application to adsorption on activated carbon in a packed column

Simulations of adsorption process using the Reynolds mass flux model described in Part I of these serial articles are presented. The object of the simulation is the methylene chloride adsorption in a packed column(0.041 m id,packed with spherical activated carbon up to a length of 0.2 m). With the Reynolds mass flux model,breakthrough/regeneration curves, concentration and temperature as well as the velocity distributions can be obtained. The simulated results are compared with the experimental data reported in the literature and satisfactory agreement is found both in breakthrough/regeneration curves and temperature curves. Moreover,the anisotropic turbulent mass diffusion is characterized and discussed.

Turbulent mixing in the upper ocean of the northwestern Weddell Sea, Antarctica

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.

Experimental Study of the Diffusion of a Confined Wall Jet through a Perforated Plate: Influence of the Porosity and the Geometry

This paper investigated lateral diffusion of a confined two-dimensional wall jet (air inlet height: 5 cm) through a perforated plate. We considered two plates with porosities of and . The plates were positioned at distances of 10 cm and 20 cm below the jet inlet. The experiments were realized using 2D Laser Doppler Anemometer (LDA). Different profiles of mean and fluctuating velocities are presented. The presence of a perforated plate strongly modified the airflow pattern compared to an empty enclosure. The velocities above and below the plate depend on several parameters, including the porosity and the plate’s position relative to the inlet slot and the longitudinal position. The difference between the flow velocity above and below the plates could not be related using a universal formula that depends on these parameters. We also investigated the influence of a porous media of a height of 20 cm (a stack of spheres having a diameter of 3.75 cm) located below the perforated plate. The results highlight that the porous medium strengthens the effects of the perforated plate on the flow.

THE DISTRIBUTION OF SOLID PARTICLES SUSPENDED IN A TURBULENT FLOW:A STOCHASTIC APPROACH

Basic fluid mechanics and stochastic theories are applied to show that the concentration distribution of suspended solid particles in a direction normal to the mean streamlines of a two-dimensional turbulent flow is greatly influenced by the lift force exerted on them in the vicinity of the wall.Analytic solution shows that,when the direction of the mean flow is horizontal,the probability density function p(y,t)for random displacements of the particles will have a maximum value at a point from the wall where the perpendicular component of the lift force precisely balances particle gravity.Interpretation of experimental observations is presented using this theory.

Prediction of Core-Annulus Solids Mass Transfer Coefficient in Gas-Solid Fluidized Bed Risers

Based on analysis of energy dissipation in the core region of gas-solid fluidized bed risers, a simplified model for determination of core-annulus solids mass transfer coefficient was developed according to turbulent diffusion mechanism of particles. The simulation results are consistent with published experimental data. Core-annulus solids mass transfer coefficient decreases with increasing particle size, particle density and solids circulation rate,but generally increases with increasing superficial gas velocity and riser diameter. In the upper dilute region of gas-solid fluidized bed risers, core-annulus solids mass transfer coefficient was found to change little with the axial coordinate in the bed.

ON DIFFUSION VELOCITY AND THE MASS CONSERVATION EQUATION FOR COMPONENTS

The mass migration velocity(absolute velocitv) of component i in a multicomponent flow is equal to the convection velocity (frame velocity) plus the diffusion velocity (relative velocity). The diffusion velocity as well as the corresponding diffusion coefficient depends on how the convection velocity is adopted.In turbulent flow, the mass migration velocity of component i is( muss-weighted time average velocity). The diffusion velocity consists of turbulent diffusion velocity and molecular diffusion velocity is the simple lime average velocity of component i and a is a certain convection velocity). So, the part of turbulent diffusion velocity is independent of what convection velocity is taken.In the mdss conservation equation for component i, the expression for the diffusion term on its right-hand side will change when the convection velocity on its left-hand side changes. In turbulent flow, there could be no diffusion terms, or a turbulent diffusion term only or both the turbulent and molecular diffusion terms when or any velocity other than these two is taken as the convection velocity. The case, in which there could he molecular diffusion only without turbulent diffusion, occurs in laminar flow. The molecular diffusion term always depends on the adoption of convection velocitv.In two-phase flow, the value of the molecular diffusion term is often near or even exceeds that of the turbulent diffusion term, which is quite different from the case in gas mixture flow.

Control of air pollution sources based on method of consecutive functional approximation

In this article the approach was used to coherent assessment based on the intensity of air pollution sources impact on the impurity concentration at a few fixed points to monitor air quality. The numerical analogue of Duhamers theorem was used to describe processes of propagation of impurity in the atmosphere. Such approach allows you to count on essential increase of calculation accuracy based on mathematical models of reasonable complexity. The inverse problem of pollutants propagation in the atmosphere based on the measurements of the impurity concentration in stationary or mobile control points was solved by the sequential function approximation The solution was presented in the form of a digital filter.

Application of the three-dimensional telegraph equation to cosmic-ray transport

An analytical solution to the three-dimensional telegraph equation is presented. This equation has recently received some attention but so far the treatment has been one-dimensional. By using the structural similarity to the Klein-Gordon equation, the telegraph equation can be solved in closed form. Illustrative examples are used to discuss the qualitative differences from the diffusion solution. A comparison with a numerical test-particle simulation reveals that some features of an intensity profile can be better explained using the telegraph approach.

Experimental and Numerical Investigation of the Diffusion of a Confined Wall Jet through a Perforated Plate

When performing numerical modeling of fluid flows where a clear medium is adjacent to a porous medium, a degree of difficulty related to the condition at the interface between the two media, where slip velocity exists, is encountered. A similar situation can be found when a jet flow interacts with a perforated plate. The numerical modeling of a perforated plate by meshing in detail each hole is most often impossible in a practical case (many holes with different shapes). Therefore, perforated plates are often modeled as porous zones with a simplified hypothesis based on pressure losses related to the normal flow through the plate. Nevertheless, previous investigations of flow over permeable walls highlight the impossibility of deducing a universal analytical law governing the slip velocity coefficient since the latter depends on many parameters such as the Reynolds number, porosity, interface structure, design of perforations, and flow direction. This makes the modeling of such a configuration difficult. The present study proposes an original numerical interface law for a perforated plate. It is used to model the turbulent jet flow interacting with a perforated plate considered as a fictitious porous medium without a detailed description of the perforations. It considers the normal and tangential effects of the flow over the plate. Validation of the model is realized through comparison with experimental data.