Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a sp...Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a specialized experimental setup capable of producing a supersonic crossflow at Mach 2.6 and a particle-laden jet with particle mass loading up to 60%is developed.Visualization of the particles motion is achieved with the help of high-speed planar laser scattering technology.The dispersion characteristics of PJSC within a supersonic channel structured by cavity are systematically analyzed through six experimental cases.The results indicate that the vortices have a significant influence on particle dispersion,leading to preferential concentration of particles.i.e.particle clusters.The particle dispersion is summarized as the"scale dispersion"pattern.The primary pathways for particles entering the cavity are identified as the shear layer above the cavity and collisions at the cavity rear edge.Among the studied factors,the momentum flux ratio exerts the most substantial influence on the dispersion process.Importantly,a reduction in the injection distance is correlated with less particles entering the cavity.The insights gained from this research provide essential references for furthering understanding particle dispersion mechanisms in supersonic flows and developing highly accurate numerical models.展开更多
高超声速转捩研究飞行器(Hypersonic Transition Research Vehicle,HyTRV)是为研究高超声速复杂三维边界层转捩而设计的升力体标模,其外形更接近真实飞行器。为深入认识HyTRV边界层稳定性特征及转捩机制,验证数值模拟和理论分析结果,本...高超声速转捩研究飞行器(Hypersonic Transition Research Vehicle,HyTRV)是为研究高超声速复杂三维边界层转捩而设计的升力体标模,其外形更接近真实飞行器。为深入认识HyTRV边界层稳定性特征及转捩机制,验证数值模拟和理论分析结果,本文在马赫数6常规风洞中,采用红外热成像技术和高频压力传感器,获得了0°和2°攻角时HyTRV标模下表面(迎风面)的边界层转捩阵面及不稳定波的演化特征,并与一维稳定性分析结果进行了对比。研究结果表明:攻角为2°时,标模下表面的横流失稳区较0°攻角时范围缩小且位置后移,标模中心线处转捩早于两侧横流区。另外,横流区存在宽频的高频信号,信号幅值在转捩完成前达到饱和。该信号包含多频段扰动,多种扰动之间相互作用导致频谱变宽,最终促使边界层转捩变为湍流。展开更多
A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined j...A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala展开更多
The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed i...The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.展开更多
The mixing and merging characteristics of multiple tandem jets in crossflow are investigated by use of the Computational Fluid Dynamics （CFD） code FI,UENT. The realizable k - ε model is employed for turbulent elosu...The mixing and merging characteristics of multiple tandem jets in crossflow are investigated by use of the Computational Fluid Dynamics （CFD） code FI,UENT. The realizable k - ε model is employed for turbulent elosure of the Reynolds-averaged Navier-Stokes equations. Numerical experiments are performed for 1-, 2- and 4-jet groups, tbr jet-tocrossflow velocity ratios of R = 4.2 ～ 16.3. The computed velocity and scalar concentration field are in good agreement with experiments using Particle Image Velocimetry （PIV） and Laser Induced Fluorescence （LIF）, as well as previous work. The results show that the leading jet behavior is similar to a single free jet in crossflow, while all the downstream rear jets have less bent-over jet trajectories - suggesting a reduced ambient velocity for the rear jets. The concentration decay of the leading jet is greater than that of the rear jets. When normalized by appropriate crossflow momentum length scales, all jet trajectories follow a universal relation regardless of the sequential order of jet position and the nund）er of jets. Supported by the velocity and trajectory measurements, the averaged maximum effective crossflow velocity ratio is computed to be in the range of 0.39 to 0.47.展开更多
Crossflow instability plays very important role in the transition of the boundary layer on a swept wing, typical in the engineering applications. Experiments revealed that the linear stability theory well predicted th...Crossflow instability plays very important role in the transition of the boundary layer on a swept wing, typical in the engineering applications. Experiments revealed that the linear stability theory well predicted the form of the crossflow vortices, but usually much overpredicted their growth rate. Using nonlinear theory of hydrodynamic stability, combined with some other considerations, we were able to obtain the growth rate in good agreement with experimental observations.展开更多
Transition prediction is a hot research topic of fluid mechanics.For subsonic and transonic aerodynamic flows,e^(N) method based on Linear Stability Theory(LST)is usually adopted reliably to predict transition.In 2013...Transition prediction is a hot research topic of fluid mechanics.For subsonic and transonic aerodynamic flows,e^(N) method based on Linear Stability Theory(LST)is usually adopted reliably to predict transition.In 2013,Coder and Maughmer established a transport equation for Tollmien-Schlichting(T-S)instability so that the e^(N) method can be applied to general Reynolds-Average-Navier-Stokes(RANS)solvers conveniently.However,this equation focuses on T-S instability,and is invalid for crossflow instability induced transition which plays a crucial role in flow instability of three-dimensional boundary layers.Subsequently,a transport equation for crossflow instability was developed in 2016,which is restricted to wing-like geometries.Then,in 2019,this model was extended to arbitrarily shaped geometries based on local variables.However,there are too many tedious functions and parameters in this version,and it can only be used for incompressible flows.Hence,in this paper,after a large amount of LST analyses and parameter optimization,an improved version for subsonic and transonic boundary layers is built.The present improved model is more robust and more concise,and it can be applied widely in aeronautical flows,which has great engineering application value and significance.An extensive validation study for this improved transition model will be performed.展开更多
Numerical simulations using volume of fluid(VOF)method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows.In this paper,large eddy simu...Numerical simulations using volume of fluid(VOF)method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows.In this paper,large eddy simulation(LES)turbulence model is coupled with the VOF method to describe the turbulence effects accurately.In addition,dynamic adaptive mesh refinement method with two refinement levels is applied to refine the size of the cells located at gas-liquid interface.Density ratio is changed from 10 to 5000 while other nondimensional numbers are kept constant.Large density ratios are considered in this paper since they are common in many practical applications such as solution precursor/suspension plasma sprays.Our simulations show that the penetration height,especially in the farfield,increases as the density ratio increases.A general correlation for the jet trajectory,which can be used for a wide range of density ratios,is developed based on our simulation results.展开更多
To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures ...To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.展开更多
The objective of this dissertation is to investigate the impinging jet under the influence of crossflow. It has been known that there exist jet shear layer, impingement on the bottom wall, interactions between the ind...The objective of this dissertation is to investigate the impinging jet under the influence of crossflow. It has been known that there exist jet shear layer, impingement on the bottom wall, interactions between the induced wall jet and the ambient crossflow in near field. There are few intensive studies of the impinging jet in crossflow at home and abroad due to the complexities of flow, such as the formation and evolution of the vortical structures, interactions among vortices, while researches on the temporal and spatial evolution of these vortical structures can promote the practical applications in environment engineering, hydroelectricity engineering, etc., and provide the basis for flow control and improvement through revealing the inherent mechanism and development of the vortical structures.展开更多
The nth-order expansion of the parabolized stability equation （EPSEn） is obtained from the Taylor expansion of the linear parabolized stability equation （LPSE） in the streamwise direction. The EPSE together with t...The nth-order expansion of the parabolized stability equation （EPSEn） is obtained from the Taylor expansion of the linear parabolized stability equation （LPSE） in the streamwise direction. The EPSE together with the homogeneous boundary conditions forms a local eigenvalue problem, in which the streamwise variations of the mean flow and the disturbance shape function are considered. The first-order EPSE （EPSE1） and the second-order EPSE （EPSE2） are used to study the crossflow instability in the swept NLF（2）-0415 wing boundary layer. The non-parallelism degree of the boundary layer is strong. Compared with the growth rates predicted by the linear stability theory （LST）, the results given by the EPSE1 and EPSE2 agree well with those given by the LPSE. In particular, the results given by the EPSE2 are almost the same as those given by the LPSE. The prediction of the EPSE1 is more accurate than the prediction of the LST, and is more efficient than the predictions of the EPSE2 and LPSE. Therefore, the EPSE1 is an efficient ey prediction tool for the crossflow instability in swept-wing boundary-layer flows.展开更多
An experimental study on the traveling crossflow instability over a 60∘swept flat plate was conducted.The Mach number is 6,the angle of attack of the model is 5∘.The traveling crossflow waves and the secondary insta...An experimental study on the traveling crossflow instability over a 60∘swept flat plate was conducted.The Mach number is 6,the angle of attack of the model is 5∘.The traveling crossflow waves and the secondary instability of the traveling crossflow waves were visualized by nano-tracer-based planar laser scattering(NPLS)technique.In the spanwise NPLS images,the traveling crossflow waves appeared as regular strikes,and the secondary instability appeared as small eddies attached to strikes.The wavelet transform was used to study the wavelength contents of the traveling crossflow waves.The most amplified wavelength is stable before the secondary instability happening,which is around 12 mm at Re_(∞)=3.45×10^(6)m^(−1).Besides,the Reynolds number effects on the boundary layer transition and traveling crossflow instability were discussed.展开更多
Numerical investigation of a transverse sonic jet injected into a supersonic crossflow was carried out using large-eddy simulation for a free-stream Mach number M=1.6 and a Reynolds number Re=1.38×10~5 based on t...Numerical investigation of a transverse sonic jet injected into a supersonic crossflow was carried out using large-eddy simulation for a free-stream Mach number M=1.6 and a Reynolds number Re=1.38×10~5 based on the jet diameter.Effects of the jet-to-crossflow momentum ratio on various fundamental mechanisms dictating the intricate flow phenomena,including flow structures,turbulent characters and frequency behaviors,have been studied.The complex flow structures and the relevant flow features are discussed to exhibit the evolution of shock structures,vortical structures and jet shear layers.The strength of the bow shock increases and the sizes of the barrel shock and Mach disk also increase with increasing momentum ratio.Turbulent characters are clarified to be closely related to the flow structures.The jet penetration increases with the increase of the momentum ratio.Moreover,the dominant frequencies of the flow structures are obtained using spectral analysis.The results obtained in this letter provide physical insight in understanding the mechanisms relevant to this complex flow.展开更多
In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are desi...In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are designed by using the orthogonal design method. The Eulerian-Lagrangian formulation is employed for modeling the droplets-crossflow two-phase flow while the realizable k-ε turbulence model is used to describe the turbulence. A new index, mixedness quality, is proposed to assess the overall mixing of the droplets in the crossflow. The simulation results demonstrate that the counter-rotating vortex pair (CVP) imposes a more significant impact on the spatial distribution than on the size distribution of the droplets. Pairs of CVP with smaller scales are preferable for achieving a better mixing. The influencing factors are listed in the following order in terms of the degree of their impact from the greatest to the least: the Sauter diameter of the initial droplets, the mixing tube diameter, the spray angle, the velocity of the inlet crossflow, and the vertical velocity of the initial droplets. A moderate droplet diameter, a smaller tube diameter, a moderate spray angle, a greater crossflow velocity and a moderate vertical velocity of the droplet are favorable for achieving a higher mixedness quality of the jet spray in a confined crossflow.展开更多
The large-scale vortical structures produced by an impinging density jet in shallow crossflow were numerically investigated in detail using RNG turbulence model. The scales, formation mechanism and evolution feature o...The large-scale vortical structures produced by an impinging density jet in shallow crossflow were numerically investigated in detail using RNG turbulence model. The scales, formation mechanism and evolution feature of the upstream wall vortex in relation to stagnation point and the Scarf vortex in near field were analyzed. The computed characteristic scales of the upstream vortex show distinguished three-dimensionality and vary with the velocity ratio and the water depth. The Scarf vortex in the near field plays an important role in the lateral concentration distributions of the impinging jet in crossflow. When the velocity ratio is relatively small, there exists a distinct lateral high concentration aggregation zone at the lateral edge between the bottom layer wall jet and the ambient crossflow, which is dominated by the Scarf vortex in the near field.展开更多
基金co-supported by the National Natural Science Foundation of China (No. 12272409)the Scientific Research and Innovation Project of Hunan Province, China (Nos. CX20230058, kq2107001, 2022RC1233 and QL20230015)
文摘Dispersion of Particle-laden Jet in Supersonic Crossflow(PJSC)is an essential process in many applications,experimental study on which,however,has rarely been reported.In order to gain physical insights into PJSC,a specialized experimental setup capable of producing a supersonic crossflow at Mach 2.6 and a particle-laden jet with particle mass loading up to 60%is developed.Visualization of the particles motion is achieved with the help of high-speed planar laser scattering technology.The dispersion characteristics of PJSC within a supersonic channel structured by cavity are systematically analyzed through six experimental cases.The results indicate that the vortices have a significant influence on particle dispersion,leading to preferential concentration of particles.i.e.particle clusters.The particle dispersion is summarized as the"scale dispersion"pattern.The primary pathways for particles entering the cavity are identified as the shear layer above the cavity and collisions at the cavity rear edge.Among the studied factors,the momentum flux ratio exerts the most substantial influence on the dispersion process.Importantly,a reduction in the injection distance is correlated with less particles entering the cavity.The insights gained from this research provide essential references for furthering understanding particle dispersion mechanisms in supersonic flows and developing highly accurate numerical models.
文摘高超声速转捩研究飞行器(Hypersonic Transition Research Vehicle,HyTRV)是为研究高超声速复杂三维边界层转捩而设计的升力体标模,其外形更接近真实飞行器。为深入认识HyTRV边界层稳定性特征及转捩机制,验证数值模拟和理论分析结果,本文在马赫数6常规风洞中,采用红外热成像技术和高频压力传感器,获得了0°和2°攻角时HyTRV标模下表面(迎风面)的边界层转捩阵面及不稳定波的演化特征,并与一维稳定性分析结果进行了对比。研究结果表明:攻角为2°时,标模下表面的横流失稳区较0°攻角时范围缩小且位置后移,标模中心线处转捩早于两侧横流区。另外,横流区存在宽频的高频信号,信号幅值在转捩完成前达到饱和。该信号包含多频段扰动,多种扰动之间相互作用导致频谱变宽,最终促使边界层转捩变为湍流。
文摘A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala
基金supported by the Science Foundation of National University of Defense Technology (No. JC11-01-02)the Hunan Provincial Natural Science Foundation of China (No.12jj4047)
文摘The transverse injection flow field has an important impact on the flowpath design of scramjet engines. At present a combination of the transverse injection scheme and any other flame holder has been widely employed in hypersonic propulsion systems to promote the mixing process between the fuel and the supersonic freestream; combustion efficiency has been improved thereby, as well as engine thrust. Research on mixing techniques for the transverse injection flow field is summarized from four aspects, namely the jet-to-crossflow pressure ratio, the geometric configuration of the injection port, the number of injection ports, and the injection angle. In conclusion, urgent investigations of mixing techniques of the transverse injection flow field are pro- posed, especiaUy data mining in the quantitative analytical results for transverse injection flow field, based on results from multi-objective design optimization theory.
基金The workis supported by a grant fromthe Hong Kong Research Grants Council (HKU7347/01E) Programfor NewCentury Excellent Talents in University (NCET-04-0494) the National Natural Science Foundation of China(Grant No.50479068)
文摘The mixing and merging characteristics of multiple tandem jets in crossflow are investigated by use of the Computational Fluid Dynamics （CFD） code FI,UENT. The realizable k - ε model is employed for turbulent elosure of the Reynolds-averaged Navier-Stokes equations. Numerical experiments are performed for 1-, 2- and 4-jet groups, tbr jet-tocrossflow velocity ratios of R = 4.2 ～ 16.3. The computed velocity and scalar concentration field are in good agreement with experiments using Particle Image Velocimetry （PIV） and Laser Induced Fluorescence （LIF）, as well as previous work. The results show that the leading jet behavior is similar to a single free jet in crossflow, while all the downstream rear jets have less bent-over jet trajectories - suggesting a reduced ambient velocity for the rear jets. The concentration decay of the leading jet is greater than that of the rear jets. When normalized by appropriate crossflow momentum length scales, all jet trajectories follow a universal relation regardless of the sequential order of jet position and the nund）er of jets. Supported by the velocity and trajectory measurements, the averaged maximum effective crossflow velocity ratio is computed to be in the range of 0.39 to 0.47.
基金The project supported by the National Natural Science Foundation of China, Grant No.19572048
文摘Crossflow instability plays very important role in the transition of the boundary layer on a swept wing, typical in the engineering applications. Experiments revealed that the linear stability theory well predicted the form of the crossflow vortices, but usually much overpredicted their growth rate. Using nonlinear theory of hydrodynamic stability, combined with some other considerations, we were able to obtain the growth rate in good agreement with experimental observations.
基金supported by the National Science Foundation for Young Scholars of China(No.:11802245)。
文摘Transition prediction is a hot research topic of fluid mechanics.For subsonic and transonic aerodynamic flows,e^(N) method based on Linear Stability Theory(LST)is usually adopted reliably to predict transition.In 2013,Coder and Maughmer established a transport equation for Tollmien-Schlichting(T-S)instability so that the e^(N) method can be applied to general Reynolds-Average-Navier-Stokes(RANS)solvers conveniently.However,this equation focuses on T-S instability,and is invalid for crossflow instability induced transition which plays a crucial role in flow instability of three-dimensional boundary layers.Subsequently,a transport equation for crossflow instability was developed in 2016,which is restricted to wing-like geometries.Then,in 2019,this model was extended to arbitrarily shaped geometries based on local variables.However,there are too many tedious functions and parameters in this version,and it can only be used for incompressible flows.Hence,in this paper,after a large amount of LST analyses and parameter optimization,an improved version for subsonic and transonic boundary layers is built.The present improved model is more robust and more concise,and it can be applied widely in aeronautical flows,which has great engineering application value and significance.An extensive validation study for this improved transition model will be performed.
文摘Numerical simulations using volume of fluid(VOF)method are performed to study the impact of liquid-to-gas density ratio on the trajectory of nonturbulent liquid jets in gaseous crossflows.In this paper,large eddy simulation(LES)turbulence model is coupled with the VOF method to describe the turbulence effects accurately.In addition,dynamic adaptive mesh refinement method with two refinement levels is applied to refine the size of the cells located at gas-liquid interface.Density ratio is changed from 10 to 5000 while other nondimensional numbers are kept constant.Large density ratios are considered in this paper since they are common in many practical applications such as solution precursor/suspension plasma sprays.Our simulations show that the penetration height,especially in the farfield,increases as the density ratio increases.A general correlation for the jet trajectory,which can be used for a wide range of density ratios,is developed based on our simulation results.
基金National Natural Science Foundation of China(51335002)
文摘To further extend knowledge about the detailed knowledge on the crossflow characteristics in a multi-jets system under a confined space,particle image velocimetry (PIV) was employed to investigate the flow structures together with the distributions of the mean velocity components for Reynolds numbers (Re) ranging from 6 213 to 13 418,nozzle-to-plate spacing (H/D) varying from 0. 20 to1. 25,respectively. Results show that the crossflow configuration is significantly different from those of large nozzle-to-plate spacing. In addition,a turning point H/D=0.50 is revealed in the profile of the normalized maximum radial velocity which is associated with the heat transfer distribution on the impingement plate.
文摘The objective of this dissertation is to investigate the impinging jet under the influence of crossflow. It has been known that there exist jet shear layer, impingement on the bottom wall, interactions between the induced wall jet and the ambient crossflow in near field. There are few intensive studies of the impinging jet in crossflow at home and abroad due to the complexities of flow, such as the formation and evolution of the vortical structures, interactions among vortices, while researches on the temporal and spatial evolution of these vortical structures can promote the practical applications in environment engineering, hydroelectricity engineering, etc., and provide the basis for flow control and improvement through revealing the inherent mechanism and development of the vortical structures.
基金supported by the National Natural Science Foundation of China(No.11332007)
文摘The nth-order expansion of the parabolized stability equation （EPSEn） is obtained from the Taylor expansion of the linear parabolized stability equation （LPSE） in the streamwise direction. The EPSE together with the homogeneous boundary conditions forms a local eigenvalue problem, in which the streamwise variations of the mean flow and the disturbance shape function are considered. The first-order EPSE （EPSE1） and the second-order EPSE （EPSE2） are used to study the crossflow instability in the swept NLF（2）-0415 wing boundary layer. The non-parallelism degree of the boundary layer is strong. Compared with the growth rates predicted by the linear stability theory （LST）, the results given by the EPSE1 and EPSE2 agree well with those given by the LPSE. In particular, the results given by the EPSE2 are almost the same as those given by the LPSE. The prediction of the EPSE1 is more accurate than the prediction of the LST, and is more efficient than the predictions of the EPSE2 and LPSE. Therefore, the EPSE1 is an efficient ey prediction tool for the crossflow instability in swept-wing boundary-layer flows.
基金This work was supported by the National Key Research and Development Plan of China(Grant 2019YFA0405300)the National Natural Science Foundation of China(Grants 11832018,12002375,11527802)the Project of National University of Defense Technology(ZK20-12).
文摘An experimental study on the traveling crossflow instability over a 60∘swept flat plate was conducted.The Mach number is 6,the angle of attack of the model is 5∘.The traveling crossflow waves and the secondary instability of the traveling crossflow waves were visualized by nano-tracer-based planar laser scattering(NPLS)technique.In the spanwise NPLS images,the traveling crossflow waves appeared as regular strikes,and the secondary instability appeared as small eddies attached to strikes.The wavelet transform was used to study the wavelength contents of the traveling crossflow waves.The most amplified wavelength is stable before the secondary instability happening,which is around 12 mm at Re_(∞)=3.45×10^(6)m^(−1).Besides,the Reynolds number effects on the boundary layer transition and traveling crossflow instability were discussed.
基金supported by the National Natural Science Foundation of China(11072236)the Fundamental Research Funds for the Central Universities(WK2090050007)
文摘Numerical investigation of a transverse sonic jet injected into a supersonic crossflow was carried out using large-eddy simulation for a free-stream Mach number M=1.6 and a Reynolds number Re=1.38×10~5 based on the jet diameter.Effects of the jet-to-crossflow momentum ratio on various fundamental mechanisms dictating the intricate flow phenomena,including flow structures,turbulent characters and frequency behaviors,have been studied.The complex flow structures and the relevant flow features are discussed to exhibit the evolution of shock structures,vortical structures and jet shear layers.The strength of the bow shock increases and the sizes of the barrel shock and Mach disk also increase with increasing momentum ratio.Turbulent characters are clarified to be closely related to the flow structures.The jet penetration increases with the increase of the momentum ratio.Moreover,the dominant frequencies of the flow structures are obtained using spectral analysis.The results obtained in this letter provide physical insight in understanding the mechanisms relevant to this complex flow.
基金Supported by the National Natural Science Foundation of China(50823002)
文摘In order to achieve uniform mixing between spray droplets and crossflow, cold-model experiment of a hollow-cone water spray in an air crossflow is investigated via a numerical simulation. The simulation cases are designed by using the orthogonal design method. The Eulerian-Lagrangian formulation is employed for modeling the droplets-crossflow two-phase flow while the realizable k-ε turbulence model is used to describe the turbulence. A new index, mixedness quality, is proposed to assess the overall mixing of the droplets in the crossflow. The simulation results demonstrate that the counter-rotating vortex pair (CVP) imposes a more significant impact on the spatial distribution than on the size distribution of the droplets. Pairs of CVP with smaller scales are preferable for achieving a better mixing. The influencing factors are listed in the following order in terms of the degree of their impact from the greatest to the least: the Sauter diameter of the initial droplets, the mixing tube diameter, the spray angle, the velocity of the inlet crossflow, and the vertical velocity of the initial droplets. A moderate droplet diameter, a smaller tube diameter, a moderate spray angle, a greater crossflow velocity and a moderate vertical velocity of the droplet are favorable for achieving a higher mixedness quality of the jet spray in a confined crossflow.
基金Project supported by the National Natural Science Foundation of China(No.10572084)Shanghai Leading Academic Discipline Project(No.Y0103)
文摘The large-scale vortical structures produced by an impinging density jet in shallow crossflow were numerically investigated in detail using RNG turbulence model. The scales, formation mechanism and evolution feature of the upstream wall vortex in relation to stagnation point and the Scarf vortex in near field were analyzed. The computed characteristic scales of the upstream vortex show distinguished three-dimensionality and vary with the velocity ratio and the water depth. The Scarf vortex in the near field plays an important role in the lateral concentration distributions of the impinging jet in crossflow. When the velocity ratio is relatively small, there exists a distinct lateral high concentration aggregation zone at the lateral edge between the bottom layer wall jet and the ambient crossflow, which is dominated by the Scarf vortex in the near field.
