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
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
An axisymmetric body at incidence experiences the three-dimensional crossflow separation. This separation is attributed to the adverse circumferential pressure gradient. However, the separation pattern is also depende...An axisymmetric body at incidence experiences the three-dimensional crossflow separation. This separation is attributed to the adverse circumferential pressure gradient. However, the separation pattern is also dependent upon the structure of the boundary layer. In this regard, utilization of transition strip devices in experiments on axisymmetric bodies may modify this structure, and consequently the crossflow separation pattern. The main objective of the present research is to mimic numerically the transition strip effect on the crossflow separation over a 6:1 prolate-spheroid up to a = 30° incidence and ReL = 4.2 x 10&. However, to avoid direct modeling of the strip, which would increase the computational cost, an attempt was made to add roughness over the body surface. To estimate the roughness that simulates closely the transition strip effect, three different roughness values were considered. The numerical model is based on RANS and a Reynolds stress turbulence model implemented in STARCCM+. The simulations have been evaluated based on the local and global variables and validated against the available experimental data. The results demonstrate the effectiveness of using a proper roughness value to mimic the transition strip effect. They also show the importance of modeling the transition strip effect, which is normally not taken into account, to capture the crossflow separation pattern.展开更多
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
The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in r...The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in real time merely by relying on traditional approaches.With the rapid advancement of deep learning technology,its powerful data processing capability offers a fast method for the prediction of the transverse jet flow field.Consequently,a prediction model based on deep learning is established,with the aim of obtaining the flow characteristics of a transverse jet under different freestream and jet conditions.This study segments the complex grid into several individual grids and trains them independently.The trained model can successfully establish the nonlinear mapping relationship between the transverse jet flow field and the input parameters.The prediction accuracy of the established model for the wall pressure under different conditions exceeds 99%,and the established model is also capable of reproducing structures such as shock waves and recirculation zones in the overall flow field,thereby achieving highly precise and efficient prediction of the jet structure and flow information.The results suggest that in contrast to the traditional numerical simulation,this deep learning model demonstrates greater efficiency in predicting the transverse jet flow field.展开更多
An experimental study on the boundary layer transition over a delta wing was carried out at Mach number 6 in a quiet wind tunnel.The Nano-tracer-based Planar Laser Scattering(NPLS)and Temperature-Sensitive Paints(TSP)...An experimental study on the boundary layer transition over a delta wing was carried out at Mach number 6 in a quiet wind tunnel.The Nano-tracer-based Planar Laser Scattering(NPLS)and Temperature-Sensitive Paints(TSP)techniques were used to measure the fine flow field structure and the wall Stanton number of the delta wing.The influence of factors such as the angle of attack and the Reynolds number was studied.The following results were obtained.The boundary layer transition between the leading edge and the centerline was dominated by the crossflow instability.At the location of the initial appearance of the traveling crossflow waves,the Stanton number began to rise.The Stanton number reached a maximum when the crossflow waves were broken up to turbulence.Increasing the angle of attack increased the spanwise pressure gradient at the windward side of the delta wing,thereby increasing the crossflow instability and advancing the boundary layer transition front.However,increasing the angle of attack caused the transition front to move backward at the leeward side.In addition,the sensitivity of the boundary layer transition to the Reynolds number varied with the angle of attack and the region.展开更多
As boundary layer transition plays an important role in aerodynamic drag prediction, the proposal and study of transition prediction methods simulating the complex flow phenomena are prerequisite for aerodynamic desig...As boundary layer transition plays an important role in aerodynamic drag prediction, the proposal and study of transition prediction methods simulating the complex flow phenomena are prerequisite for aerodynamic design. In this paper, with the application of the linear stability theory based on amplification factor transport transition equations on the two-equation shear stress transport (SST) eddy-viscosity model, a new method, the SST-NTS-NCF model, is yielded. The new amplification factor transport equation for the crossflow instability induced transition is proposed to add to the NTS equation proposed by Coder, which simulates Tollmien-Schlichting wave transition. The turbulent kinetic energy equation is modified by introducing a new source term that simulates the transition process without the intermittency factor equation. Finally, coupled with these two amplification factor transport equations and SST turbulence model, a four-equation transition turbulence model is built. Comparisons between predictions using the new model and wind-tunnel experiments of NACA64(2) A015, NLF(2)-0415 and ONERA-D infinite swept wing and ONERAM6 swept wing validate the predictive quality of the new SST-NTS-NCF model. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.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
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
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
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
Due to its high computational efficiency and ability to consider nonparallel and nonlinear effects, nonlinear parabolized stability equations（NPSE） approach has been widely used to study the stability and transition...Due to its high computational efficiency and ability to consider nonparallel and nonlinear effects, nonlinear parabolized stability equations（NPSE） approach has been widely used to study the stability and transition mechanisms. However,it often diverges in hypersonic boundary layers when the amplitude of disturbance reaches a certain level. In this study, an improved algorithm for solving NPSE is developed. In this algorithm, the mean flow distortion is included into the linear operator instead of into the nonlinear forcing terms in NPSE. An under-relaxation factor for computing the nonlinear terms is introduced during the iteration process to guarantee the robustness of the algorithm. Two case studies, the nonlinear development of stationary crossflow vortices and the fundamental resonance of the second mode disturbance in hypersonic boundary layers, are presented to validate the proposed algorithm for NPSE. Results from direct numerical simulation（DNS） are regarded as the baseline for comparison. Good agreement can be found between the proposed algorithm and DNS, which indicates the great potential of the proposed method on studying the crossflow and streamwise instability in hypersonic boundary layers.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
It is widely accepted that a robust and efficient method to compute the linear spatial amplified rate ought to be developed in three-dimensional （3D） boundary layers to predict the transition with the e^N method, es...It is widely accepted that a robust and efficient method to compute the linear spatial amplified rate ought to be developed in three-dimensional （3D） boundary layers to predict the transition with the e^N method, especially when the boundary layer varies significantly in the spanwise direction. The 3D-linear parabolized stability equation （3D- LPSE） approach, a 3D extension of the two-dimensional LPSE （2D-LPSE）, is developed with a plane-marching procedure for investigating the instability of a 3D boundary layer with a significant spanwise variation. The method is suitable for a full Mach number region, and is validated by computing the unstable modes in 2D and 3D boundary layers, in both global and local instability problems. The predictions are in better agreement with the ones of the direct numerical simulation （DNS） rather than a 2D-eigenvalue problem （EVP） procedure. These results suggest that the plane-marching 3D-LPSE approach is a robust, efficient, and accurate choice for the local and global instability analysis in 2D and 3D boundary layers for all free-stream Mach numbers.展开更多
This paper aims at probing the flow characteristics of a jet in supersonic crossflow(JISC)by installing a vortex generator(VG)upstream of the jet orifice.Nanoparticle planar laser scattering(NPLS)and stereo-particle i...This paper aims at probing the flow characteristics of a jet in supersonic crossflow(JISC)by installing a vortex generator(VG)upstream of the jet orifice.Nanoparticle planar laser scattering(NPLS)and stereo-particle image velocimetry(SPIV)technologies were employed to observe the flowfield,and three cases were designed for comparison.CASE0 stands for JISC without passive VG.In CASE1 and CASE2,VG is installed at 20 mm and 80 mm upstream away from the jet orifice,respectively.Transient flow structures show that two flow modes exist when the VG wake interacts with the JISC.In CASE1,vortices are induced from both sides of the jet plume because of the VG wake.This leads to a complex streamwise vortex system.Penetration and lateral diffusion are enhanced.In CASE2,intermittent large-scale eddies in the VG wake cause large streamwise vortices at the windward side of the jet.The penetration depth is also enhanced while the lateral diffusion is restrained.In addition,experimental results show that the penetration depth is approximately 8.5%higher in CASE1 than that in CASE0,and the lateral diffusion is larger by about 17.0%.In CASE2,the penetration is increased by about 26.2%,while the lateral diffusion is enhanced by just 0.5%.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 oily wastewater generated from pretreatment unit of electrocoating industry contains oils, phosphate, organic solvents, and surfactants. In order to improve the removal efficiencies of phosphate and oils, to mitig...The oily wastewater generated from pretreatment unit of electrocoating industry contains oils, phosphate, organic solvents, and surfactants. In order to improve the removal efficiencies of phosphate and oils, to mitigate the membrane fouling, coagulation for ceramic membrane microfiltration of oily wastewater was performed. The results of filtration tests show that the membrane fouling decreased and the permeate flux and quality increased with coagulation as pretreatment. At the coagulant Ca （OH）2 dosage of 900 mg/L, the removal efficiency of phosphate was increased from 46.4% without coagulation to 99.6%; the removal of COD and oils were 97.0% and 99.8%, respectively. And the permeate flux was about 70% greater than that when Ca（OH）2 was not used. The permeate obtained from coagulation and microfiltration can be reused as make-up water, and the recommended operation conditions for pilot and industrial application are transmembrane pressure of 0.10 MPa and cross-flow velocity of 5 m/s. The comparison results show that 0.2 μm ZrO2 microfilter with coagulation could be used to perform the filtration rather than conventional ultrafilter, with very substantial gain in flux and removal efficiency of phosphate.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
To study statistical characteristics of the random spray autoignition,aviation kerosene was injected transiently into non-vitiated air crossflow in a flow reactor with optical accesses.The operating conditions were re...To study statistical characteristics of the random spray autoignition,aviation kerosene was injected transiently into non-vitiated air crossflow in a flow reactor with optical accesses.The operating conditions were relevant to gas turbine combustor:the air crossflow pressure and temperature were in the range of 1.4-1.7 MPa and 830-947 K,respectively,and the jet-tocrossflow momentum flux ratios were 20,50 and 80.Statistical distributions of random ignition delay times with adequate convergence were estimated based on histograms.The dependences of the distributions on reactor pressure,temperature,and jet-to-crossflow momentum flux ratio were studied.The results show that the resulting distributions appear more concentrated with the increase of air temperature or jet-to-crossflow momentum flux ratio.And then the correlations for the mean and standard deviation of the ignition delay time sample data were developed based on the present results.Compared with the correlations of ignition delay time of homogeneous premixed gas-phase kerosene/air mixture reported in the literature,the results show a greater significance pressure dependence and lower temperature sensitivity of the ignition delay time of nonpremixed kerosene spray.展开更多
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.
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.
文摘An axisymmetric body at incidence experiences the three-dimensional crossflow separation. This separation is attributed to the adverse circumferential pressure gradient. However, the separation pattern is also dependent upon the structure of the boundary layer. In this regard, utilization of transition strip devices in experiments on axisymmetric bodies may modify this structure, and consequently the crossflow separation pattern. The main objective of the present research is to mimic numerically the transition strip effect on the crossflow separation over a 6:1 prolate-spheroid up to a = 30° incidence and ReL = 4.2 x 10&. However, to avoid direct modeling of the strip, which would increase the computational cost, an attempt was made to add roughness over the body surface. To estimate the roughness that simulates closely the transition strip effect, three different roughness values were considered. The numerical model is based on RANS and a Reynolds stress turbulence model implemented in STARCCM+. The simulations have been evaluated based on the local and global variables and validated against the available experimental data. The results demonstrate the effectiveness of using a proper roughness value to mimic the transition strip effect. They also show the importance of modeling the transition strip effect, which is normally not taken into account, to capture the crossflow separation pattern.
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.
基金co-supported by the National Natural Science Foundation of China(No.12202488)the National Postdoctoral Researcher Program(Grants No.GZB20230985)+1 种基金the Natural Science Program of National University of Defense Technology(No.ZK22-30)the Independent Innovation Science Fund of National University of Defense Technology(No.24-ZZCX-BC-05)。
文摘The complex flow characteristics of transverse jet in high-speed crossflow involve several separation regions and multiple shock waves,which make it difficult to capture and precisely predict the flow field state in real time merely by relying on traditional approaches.With the rapid advancement of deep learning technology,its powerful data processing capability offers a fast method for the prediction of the transverse jet flow field.Consequently,a prediction model based on deep learning is established,with the aim of obtaining the flow characteristics of a transverse jet under different freestream and jet conditions.This study segments the complex grid into several individual grids and trains them independently.The trained model can successfully establish the nonlinear mapping relationship between the transverse jet flow field and the input parameters.The prediction accuracy of the established model for the wall pressure under different conditions exceeds 99%,and the established model is also capable of reproducing structures such as shock waves and recirculation zones in the overall flow field,thereby achieving highly precise and efficient prediction of the jet structure and flow information.The results suggest that in contrast to the traditional numerical simulation,this deep learning model demonstrates greater efficiency in predicting the transverse jet flow field.
基金supported by the National Key Technology Research and Development Program of China(No.2016YFA0401200)the National Project for Research and Development of Major Scientific Instruments of China(No.11527802)the National Natural Science Foundation of China(Nos.91752102 and 11832018)。
文摘An experimental study on the boundary layer transition over a delta wing was carried out at Mach number 6 in a quiet wind tunnel.The Nano-tracer-based Planar Laser Scattering(NPLS)and Temperature-Sensitive Paints(TSP)techniques were used to measure the fine flow field structure and the wall Stanton number of the delta wing.The influence of factors such as the angle of attack and the Reynolds number was studied.The following results were obtained.The boundary layer transition between the leading edge and the centerline was dominated by the crossflow instability.At the location of the initial appearance of the traveling crossflow waves,the Stanton number began to rise.The Stanton number reached a maximum when the crossflow waves were broken up to turbulence.Increasing the angle of attack increased the spanwise pressure gradient at the windward side of the delta wing,thereby increasing the crossflow instability and advancing the boundary layer transition front.However,increasing the angle of attack caused the transition front to move backward at the leeward side.In addition,the sensitivity of the boundary layer transition to the Reynolds number varied with the angle of attack and the region.
基金supported by the National Basic Research Program of China (No. 2014CB744804)
文摘As boundary layer transition plays an important role in aerodynamic drag prediction, the proposal and study of transition prediction methods simulating the complex flow phenomena are prerequisite for aerodynamic design. In this paper, with the application of the linear stability theory based on amplification factor transport transition equations on the two-equation shear stress transport (SST) eddy-viscosity model, a new method, the SST-NTS-NCF model, is yielded. The new amplification factor transport equation for the crossflow instability induced transition is proposed to add to the NTS equation proposed by Coder, which simulates Tollmien-Schlichting wave transition. The turbulent kinetic energy equation is modified by introducing a new source term that simulates the transition process without the intermittency factor equation. Finally, coupled with these two amplification factor transport equations and SST turbulence model, a four-equation transition turbulence model is built. Comparisons between predictions using the new model and wind-tunnel experiments of NACA64(2) A015, NLF(2)-0415 and ONERA-D infinite swept wing and ONERAM6 swept wing validate the predictive quality of the new SST-NTS-NCF model. (C) 2016 Chinese Society of Aeronautics and Astronautics. Production and hosting by Elsevier Ltd.
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 Natural Science Foundation of China(Grant Nos.11332007 and 11402167)
文摘Due to its high computational efficiency and ability to consider nonparallel and nonlinear effects, nonlinear parabolized stability equations（NPSE） approach has been widely used to study the stability and transition mechanisms. However,it often diverges in hypersonic boundary layers when the amplitude of disturbance reaches a certain level. In this study, an improved algorithm for solving NPSE is developed. In this algorithm, the mean flow distortion is included into the linear operator instead of into the nonlinear forcing terms in NPSE. An under-relaxation factor for computing the nonlinear terms is introduced during the iteration process to guarantee the robustness of the algorithm. Two case studies, the nonlinear development of stationary crossflow vortices and the fundamental resonance of the second mode disturbance in hypersonic boundary layers, are presented to validate the proposed algorithm for NPSE. Results from direct numerical simulation（DNS） are regarded as the baseline for comparison. Good agreement can be found between the proposed algorithm and DNS, which indicates the great potential of the proposed method on studying the crossflow and streamwise instability in hypersonic boundary layers.
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Project supported by the National Natural Science Foundation of China(Nos.11272183,11572176,11402167,11202147,and 11332007)the National Program on Key Basic Research Project of China(No.2014CB744801)
文摘It is widely accepted that a robust and efficient method to compute the linear spatial amplified rate ought to be developed in three-dimensional （3D） boundary layers to predict the transition with the e^N method, especially when the boundary layer varies significantly in the spanwise direction. The 3D-linear parabolized stability equation （3D- LPSE） approach, a 3D extension of the two-dimensional LPSE （2D-LPSE）, is developed with a plane-marching procedure for investigating the instability of a 3D boundary layer with a significant spanwise variation. The method is suitable for a full Mach number region, and is validated by computing the unstable modes in 2D and 3D boundary layers, in both global and local instability problems. The predictions are in better agreement with the ones of the direct numerical simulation （DNS） rather than a 2D-eigenvalue problem （EVP） procedure. These results suggest that the plane-marching 3D-LPSE approach is a robust, efficient, and accurate choice for the local and global instability analysis in 2D and 3D boundary layers for all free-stream Mach numbers.
基金supported by the National Natural Science Foundation of China(Nos.91541203 and 51676204)the Fenglei Youth Innovation Fund of China Aerodynamics Research and Development Center(No.PJD20170186)。
文摘This paper aims at probing the flow characteristics of a jet in supersonic crossflow(JISC)by installing a vortex generator(VG)upstream of the jet orifice.Nanoparticle planar laser scattering(NPLS)and stereo-particle image velocimetry(SPIV)technologies were employed to observe the flowfield,and three cases were designed for comparison.CASE0 stands for JISC without passive VG.In CASE1 and CASE2,VG is installed at 20 mm and 80 mm upstream away from the jet orifice,respectively.Transient flow structures show that two flow modes exist when the VG wake interacts with the JISC.In CASE1,vortices are induced from both sides of the jet plume because of the VG wake.This leads to a complex streamwise vortex system.Penetration and lateral diffusion are enhanced.In CASE2,intermittent large-scale eddies in the VG wake cause large streamwise vortices at the windward side of the jet.The penetration depth is also enhanced while the lateral diffusion is restrained.In addition,experimental results show that the penetration depth is approximately 8.5%higher in CASE1 than that in CASE0,and the lateral diffusion is larger by about 17.0%.In CASE2,the penetration is increased by about 26.2%,while the lateral diffusion is enhanced by just 0.5%.
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 oily wastewater generated from pretreatment unit of electrocoating industry contains oils, phosphate, organic solvents, and surfactants. In order to improve the removal efficiencies of phosphate and oils, to mitigate the membrane fouling, coagulation for ceramic membrane microfiltration of oily wastewater was performed. The results of filtration tests show that the membrane fouling decreased and the permeate flux and quality increased with coagulation as pretreatment. At the coagulant Ca （OH）2 dosage of 900 mg/L, the removal efficiency of phosphate was increased from 46.4% without coagulation to 99.6%; the removal of COD and oils were 97.0% and 99.8%, respectively. And the permeate flux was about 70% greater than that when Ca（OH）2 was not used. The permeate obtained from coagulation and microfiltration can be reused as make-up water, and the recommended operation conditions for pilot and industrial application are transmembrane pressure of 0.10 MPa and cross-flow velocity of 5 m/s. The comparison results show that 0.2 μm ZrO2 microfilter with coagulation could be used to perform the filtration rather than conventional ultrafilter, with very substantial gain in flux and removal efficiency of phosphate.
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supported by the National Natural Science Foundation of China(Nos.91641109 and 61827802)。
文摘To study statistical characteristics of the random spray autoignition,aviation kerosene was injected transiently into non-vitiated air crossflow in a flow reactor with optical accesses.The operating conditions were relevant to gas turbine combustor:the air crossflow pressure and temperature were in the range of 1.4-1.7 MPa and 830-947 K,respectively,and the jet-tocrossflow momentum flux ratios were 20,50 and 80.Statistical distributions of random ignition delay times with adequate convergence were estimated based on histograms.The dependences of the distributions on reactor pressure,temperature,and jet-to-crossflow momentum flux ratio were studied.The results show that the resulting distributions appear more concentrated with the increase of air temperature or jet-to-crossflow momentum flux ratio.And then the correlations for the mean and standard deviation of the ignition delay time sample data were developed based on the present results.Compared with the correlations of ignition delay time of homogeneous premixed gas-phase kerosene/air mixture reported in the literature,the results show a greater significance pressure dependence and lower temperature sensitivity of the ignition delay time of nonpremixed kerosene spray.
