A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whet...A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.展开更多
Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind for...Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downweUing jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 26s-36s （Stokes depth scale） and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy （TKE） generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Krn are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear （S2） near the SML base. In addition, the large-scale eddies and Sz induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.展开更多
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
2nd-order upwind TVD scheme was used to solve the laminar, fully Navier-Stokes equations. The numerical simulations were done on the propagation of a shock wave with Ma(s) = 2 and 4 into a hydrogen and air mixture in ...2nd-order upwind TVD scheme was used to solve the laminar, fully Navier-Stokes equations. The numerical simulations were done on the propagation of a shock wave with Ma(s) = 2 and 4 into a hydrogen and air mixture in a duct and a duct with a rearward step. The results indicate that a swirling vortex: may be generated in the lopsided interface behind the moving shock. Meanwhile, the complex shock system is also formed in this shear flow region. A large swirling vortex is produced and the fuel mixing can be enhanced by a shock wave at low Mach number. But in a duct with a rearward step, the shock almost disappears in hydrogen for Mns = 2. The shack in hydrogen will become strong if Ma(s) is large. Similar to the condition of a shock moving in a duct full of hydrogen and air, a large vortex cart be formed in the shear flow region. The large swirling vortex even gets through the reflected shock and impacts on the lower wall. Then, the distribution of hydrogen behind the rearward step is divided into two regions. The transition from regular reflection to Mach reflection was observed aswell in case Ma(s) = 4.展开更多
The coherent structures and the chaotic phenomena in the transition of the axisymmetric countercurrent mixing shear flow were investigated experimentally. Two kinds of self-excited oscillation modes could exist in the...The coherent structures and the chaotic phenomena in the transition of the axisymmetric countercurrent mixing shear flow were investigated experimentally. Two kinds of self-excited oscillation modes could exist in the axisymmetric countercurrent mixing shear flow. One is the shear layer self-excited oscillation mode corresponding to the high Reynolds number regime and the other is the jet column self-excited oscillation mode corresponding to the low Reynolds number regime in the case of the velocity ratio ranging from I to 1.5. Analyzing the auto-power spectrum, self-correlation-function and three dimensional reconstructed phase trajectory, the route to chaos through three Hopf bifurcations intercepted by an intermittence of the dynamical system corresponding to the axisymmetric countercurrent mixing shear flow was discovered when the velocity ratio is equal to 1.32.展开更多
The theoretical investigation of the role of three-dimensional large-scale coherent structures and their mutual interactions in a developing plane mixing layer subjected to external forcing is presented. Large-scale c...The theoretical investigation of the role of three-dimensional large-scale coherent structures and their mutual interactions in a developing plane mixing layer subjected to external forcing is presented. Large-scale coherent structures are decomposed into 3 fundamental and 2 subharmoic wave modes. A parametric study is carried out examining effects of a multitude of initial conditions. It is found that the evolution of the forced three-dimensional shear layer and the associated local entrainment can be influenced greatly by the initial amplitudes and phases of the large-scale modes. The presence of three-dimensional modes may have a profound effect on shear layer growth when forced at amplitudes comparable or larger than those of the two-dimensional ones. This effect is more pronounced at low frequency. Nonlinear interactions between the fundamentals and subharmonics indicate that subharmonics of the most amplified frequency of the shear layer are usually produced during the early stages of flow development, while its harmonics are always produced far downstream, regardless of initial conditions. The results of this study provide useful parametric information for the control, through multi-mode forcing, of shear layers in practical applications, aiming at mixing and transport augmentation.展开更多
The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow paramete...The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.展开更多
文摘A spectrum method is used to simulate the time-developing free mixing layerwith cross shear which is introduced in different stages. The results show that the properties of flow are nearly the same for situations whether the cross shear is introduced in theinitial time or in early stage. If cross shear is introduced in the stage that the roll-up ofmixing layer occurs, the turbulent intensities of now will increase and mixture of now willbe enhanced.
基金The National Basic Research Program of China(973 Program)under contract No.2011CB403504the China Postdoctoral Science Foundation under contract No.2013M542216the National Natural Science Foundation of China under contract No.41206011
文摘Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downweUing jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 26s-36s （Stokes depth scale） and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy （TKE） generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Krn are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear （S2） near the SML base. In addition, the large-scale eddies and Sz induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.
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theNationalNaturalScienceFoundationofChina(1 9882 0 0 5 ) China 863High_TecProject (863_2 .99.9)
文摘2nd-order upwind TVD scheme was used to solve the laminar, fully Navier-Stokes equations. The numerical simulations were done on the propagation of a shock wave with Ma(s) = 2 and 4 into a hydrogen and air mixture in a duct and a duct with a rearward step. The results indicate that a swirling vortex: may be generated in the lopsided interface behind the moving shock. Meanwhile, the complex shock system is also formed in this shear flow region. A large swirling vortex is produced and the fuel mixing can be enhanced by a shock wave at low Mach number. But in a duct with a rearward step, the shock almost disappears in hydrogen for Mns = 2. The shack in hydrogen will become strong if Ma(s) is large. Similar to the condition of a shock moving in a duct full of hydrogen and air, a large vortex cart be formed in the shear flow region. The large swirling vortex even gets through the reflected shock and impacts on the lower wall. Then, the distribution of hydrogen behind the rearward step is divided into two regions. The transition from regular reflection to Mach reflection was observed aswell in case Ma(s) = 4.
文摘The coherent structures and the chaotic phenomena in the transition of the axisymmetric countercurrent mixing shear flow were investigated experimentally. Two kinds of self-excited oscillation modes could exist in the axisymmetric countercurrent mixing shear flow. One is the shear layer self-excited oscillation mode corresponding to the high Reynolds number regime and the other is the jet column self-excited oscillation mode corresponding to the low Reynolds number regime in the case of the velocity ratio ranging from I to 1.5. Analyzing the auto-power spectrum, self-correlation-function and three dimensional reconstructed phase trajectory, the route to chaos through three Hopf bifurcations intercepted by an intermittence of the dynamical system corresponding to the axisymmetric countercurrent mixing shear flow was discovered when the velocity ratio is equal to 1.32.
文摘The theoretical investigation of the role of three-dimensional large-scale coherent structures and their mutual interactions in a developing plane mixing layer subjected to external forcing is presented. Large-scale coherent structures are decomposed into 3 fundamental and 2 subharmoic wave modes. A parametric study is carried out examining effects of a multitude of initial conditions. It is found that the evolution of the forced three-dimensional shear layer and the associated local entrainment can be influenced greatly by the initial amplitudes and phases of the large-scale modes. The presence of three-dimensional modes may have a profound effect on shear layer growth when forced at amplitudes comparable or larger than those of the two-dimensional ones. This effect is more pronounced at low frequency. Nonlinear interactions between the fundamentals and subharmonics indicate that subharmonics of the most amplified frequency of the shear layer are usually produced during the early stages of flow development, while its harmonics are always produced far downstream, regardless of initial conditions. The results of this study provide useful parametric information for the control, through multi-mode forcing, of shear layers in practical applications, aiming at mixing and transport augmentation.
文摘The paper deals with experimental and numerical results of investigation into supersonic and transonic flow past a two-dimensional model ejector. Results of optical measurements show a flow structure and flow parameter development in the entrance part of the mixing chamber of the ejector. Numerical results are obtained by means of both the straight solution of shock waves in supersonic flow field using classical relations of parameters of shock waves and the Fluent 6 program. Results of numerical solutions are compared with experimental pictures of flow fields. Flow structure development in the mixing chamber is analysed in detail.
