In this paper,some typical methods to promote mixing in supersonic combustion are reviewed,and the fluid-dynamic mechanism underpinning the development of the supersonic shear layer in the presence of a streamwise vor...In this paper,some typical methods to promote mixing in supersonic combustion are reviewed,and the fluid-dynamic mechanism underpinning the development of the supersonic shear layer in the presence of a streamwise vortex is analyzed through computational fluid dynamics.It is proven that the streamwise vortex-couple method is an excellent approach to enhance mixing.A specific combustor design is proposed accordingly.展开更多
The generation of a hairpin vortex from near-wall streamwise vortices is studied via the direct numerical simulation（DNS） of the streak transient growth in the minimal channel flow at Re_τ- 400.The streak profile i...The generation of a hairpin vortex from near-wall streamwise vortices is studied via the direct numerical simulation（DNS） of the streak transient growth in the minimal channel flow at Re_τ- 400.The streak profile is obtained by conditionally averaging the DNS data of the fully developed turbulent channel flow at the same Reynolds number.The near-wall streamwise vortices are produced by the transient growth of the streak which is initially subjected to the sinuous perturbation of the spanwise velocity.It is shown that the arch head of the hairpin vortex first grows from the downstream end of the stronger streamwise vortex and then connects with the weaker,opposite-signed streamwise vortex in their overlap region,forming a complete individual hairpin structure.The vorticity transport along the vortex lines indicates that the strength increase and the spatial expansion of the arch head are due to the stretching and the turning of the vorticity vector,respectively.The hairpin packets could be further produced from the generated individual hairpin vortex following the parent-offspring process.展开更多
A mechanism for generation of near wall quasi-streamwise hairpin-like vortex （QHV） and secondary quasi-streamwise vortices （SQV） is presented. The conceptual model of resonant triad in the theory of hydrodynamic i...A mechanism for generation of near wall quasi-streamwise hairpin-like vortex （QHV） and secondary quasi-streamwise vortices （SQV） is presented. The conceptual model of resonant triad in the theory of hydrodynamic instability and direct numerical simulation of a turbulent boundary layer were applied to reveal the formation of QHV and SQV. The generation procedures and the characteristics of the vortex structures are obtained, which share some similarities with previous numerical simulations. The research using resonant triad conceptual model and numerical simulation provides a possibility for investigating and controling the vortex structures, which play a dominant role in the evolution of coherent structures in the near-wall region.展开更多
How control in turbomachinery is very difficult because of the complexity of its fully 3-D flow structure. The authors propose to introduce streamwise vortices into the control of internal flows. A simple configuratio...How control in turbomachinery is very difficult because of the complexity of its fully 3-D flow structure. The authors propose to introduce streamwise vortices into the control of internal flows. A simple configuration of vortices was investigated in order to better understand the flow control methods by means of streamwise vortices. The research presented here concerns streamwise vortex interaction with a horseshoe vortex. The effects of such an interaction are significantly dependent on the relative location of the streamwise vortex in respect to the leading edge of the profile. The streamwise vortex is induced by an air jet. The horseshoe vortex is generated by the leading edge of a symmetric profile. Such a configuration gives possibility to investigate the interaction of these two vortices alone. The presented analysis is based on numerical simulations by means of N-S compressible solver with a two-equation turbulence model.展开更多
Formation and evolution of secondary streamwise vortices in the compressible transitional boundary layers over a flat plate are studied using a direct numerical simu- lation method with high-order accuracy and highly ...Formation and evolution of secondary streamwise vortices in the compressible transitional boundary layers over a flat plate are studied using a direct numerical simu- lation method with high-order accuracy and highly effective non-reflecting characteristic boundary conditions. Generation and development processes of the secondary streamwise vortices in the complicated transitional boundary flow are clearly analyzed based on the of numerical results, and the effects on the formation of the ring-like vortex that is vital to the boundary layer transition are explored. A new mechanism forming the ring-like vortex through the mutual effect of the primary and secondary streamwise vortices is expressed.展开更多
The mixing effectiveness of the airflow between the inner and outer bypass inlets of a Rear Variable-Area Bypass Injector(RVABI)is the key to the afterburner performance of variable cycle engines.This paper describes ...The mixing effectiveness of the airflow between the inner and outer bypass inlets of a Rear Variable-Area Bypass Injector(RVABI)is the key to the afterburner performance of variable cycle engines.This paper describes an optimized RVABI design based on an alternating area regulator to improve the velocity/temperature uniformity of the incoming flow at the afterburner.Compared with a classical RVABI,numerical simulations show that the proposed alternating RVABI performs better in terms of thermal mixing efficiency and total pressure loss in different variable cycle engine modes.Both the increasing air contact area between the inner and outer bypass of alternating structure RVABI,and a larger streamwise vortex in the inner bypass inlet due to the proposed alternating lobe structure in the RVABI contribute to the significantly increase of mixing effectiveness.Besides,the alternating regulator induces strong streamwise vortex,which helps to improve the airflow mixing with its vortex-induced velocity.The interaction between the streamwise vortex and azimuthal vortex further promises the velocity/temperature uniformity after the RVABI.With the increase of alternating lobe’s height ratio,the covering area of the streamwise vortex and the azimuthal vortex is enlarged,which further enhances the thermal mixing efficiency of the RVABI.This design gives an insight into the future design and optimization of RVABI.展开更多
Turbulent spots play a key role in the formation of the turbulence and the transition. The generation and evolution of turbulent spots using the wall impulse model in the plane Couette flow are studied by direct numer...Turbulent spots play a key role in the formation of the turbulence and the transition. The generation and evolution of turbulent spots using the wall impulse model in the plane Couette flow are studied by direct numerical simulation of Navier-Stokes equations. A group of three-dimensional coupling compact difference schemes with high accuracy and high resolution is used in the numerical calculation. The important characteristics of turbulent spots based on the results of examples are analyzed, including the formation of random pulse, the generation of Reynolds stress, the growth of disturbance amplitude, and the continuous change of spot shape, especially the complex evolution process of the streamwise vortices. Computational results confirm that basic properties of turbulent spots in the laminar flow are similar to those in the turbulent flow.展开更多
The performance of an annular jet pump( AJP) is determined by its area ratio A( ratio of cross sectional area of throat and annular nozzle) and flow rate ratio q( ratio of primary and secondary flow rate,Qs/Qj),while ...The performance of an annular jet pump( AJP) is determined by its area ratio A( ratio of cross sectional area of throat and annular nozzle) and flow rate ratio q( ratio of primary and secondary flow rate,Qs/Qj),while the nozzle lip thickness is neglected in the present studies. This paper presents a study on the effect of the thickness on the flow field and performance of an AJP with A = 1. 75. With the increasing flow rate ratio and nozzle lip thickness,a small vortex forms at the nozzle lip and keeps on growing. However,as the flow rate ratio or nozzle lip thickness is extremely low,the vortex at the lip vanishes thoroughly. Moreover,the recirculation width varies conversely with the nozzle lip thickness when the flow rate ratio q ≤ 0. 13. While the deviation of the recirculation width with different nozzle lip thickness is negligible with q ≥ 0. 13. Additionally the existence of nozzle lip hinders the momentum exchange between the primary and secondary flow and leads to a mutation of velocity gradient near the nozzle exit,which shift the recirculation downstream. Finally,based on the numerical results of the streamwise and spanwise vortex distributions in the suction chamber, the characteristics of the mixing process and the main factors accounting for the AJP performance are clarified.展开更多
In order to investigate the effects of the airfoil-probes on the aerodynamic performance of an axial compressor,a numerical simulation of 3D flow field is performed in a 1.5-stage axial compressor with airfoil-probes ...In order to investigate the effects of the airfoil-probes on the aerodynamic performance of an axial compressor,a numerical simulation of 3D flow field is performed in a 1.5-stage axial compressor with airfoil-probes installed at the stator leading-edge（LE）.The airfoil-probes have a negative influence on the compressor aerodynamic performance at all operating points.A streamwise vortex is induced by the airfoil-probe along both sides of the blade.At the mid-operating point,the vortex is notable along the pressure side and is relatively small along the suction side（SS）.At the near-stall point,the vortex is slightly suppressed in the pressure surface（PS）,but becomes remarkable in the suction side.A small local-separation is induced by the interactions between the vortex and the end-wall boundary layer in the corner region near the hub.That the positive pitch angle of the airfoil-probe at 6.5% span is about 15° plays an important role in the vortex evolution near the hub,which causes the fact that the airfoil-probe near the hub has the largest effects among the four airfoil-probes.In order to get a further understanding of the vortex evolution in the stator in the numerical simulation,a flow visualization experiment in a water tunnel is performed.The flow visualization results give a deep insight into the evolution of the vortex induced by the airfoil-probe.展开更多
The air-turbo-rocket(ATR)engine is a promising propulsion plant for achieving numerous surface and air launched missile missions.The application of lobed mixer in the ATR combustor can promote the mixing of the fuelri...The air-turbo-rocket(ATR)engine is a promising propulsion plant for achieving numerous surface and air launched missile missions.The application of lobed mixer in the ATR combustor can promote the mixing of the fuelrich gas and the air,thus improving the engine performance significantly.The numerical simulation method was conducted to explore the effects of lobe peak-to-trough width ratio on mixing and combustion performance in ATR combustors.Results show that:For a given peak lobe width b1,the combustion efficiency and total pressure loss decrease with the increase of trough lobe width b2;For a given b2,the combustion efficiency and total pressure loss decrease with the increase of b1;The fan-type lobed mixer with smaller b2has a better effect on promoting the combustion efficiency in the region near the ATR combustor center line than that with a pair of parallel side walls.The total pressure recovery coefficient reaches more than 0.99 at the exit of combustor in nonreactive combustion while the total pressure loss reaches more than 4%in the reacting combustion.Compared with the mixing process,more than80%of the total pressure loss is caused during combustion.展开更多
In this study,the delayed detached eddy simulation(DDES)is coupled with a homogenous cavitation model to simulate the cavitating turbulent flow around a propeller behind a full body ship with special emphasis on the i...In this study,the delayed detached eddy simulation(DDES)is coupled with a homogenous cavitation model to simulate the cavitating turbulent flow around a propeller behind a full body ship with special emphasis on the influence of the vortex generator(VG)on the propeller cavitation and the hull pressure fluctuation.The small calculation uncertainty as evaluated by the DDES verification and validation(V&V)method indicates that the present simulation can accurately reproduce the propeller performance and cavitation,and the predicted hull pressure fluctuation is in a fairly good agreement with the available experimental data.The mechanism is explored through the current numerical results how the VG affects the local velocity distribution,along with the influences of the VG on the propeller cavitation and the hull pressure fluctuation.It is shown that the streamwise vortex is induced by the VG near the hull boundary layer.The very low velocity region in the hull wake is reduced due to the effect of the streamwise vortex.Besides,the propeller cavitation develops more mildly and the hull pressure fluctuation decreases due to the influence of the VG.展开更多
The alternating wedge strut,serving as both an injector and a vortex generator,has great potential for application in the scramjet combustor.The expansive trailing edge structure can further enhance the mixing perform...The alternating wedge strut,serving as both an injector and a vortex generator,has great potential for application in the scramjet combustor.The expansive trailing edge structure can further enhance the mixing performance of the alternating wedge strut.To enhance the performance of scramjet engines,it is essential to investigate the fuel/air mixing characteristics and mechanism downstream of alternating wedge struts with expansive trailing edges.The research focused on the impact of two different fuel injection schemes on the air/fuel mixing process and plume morphology.The optical diagnostic technique,particle laser-induced fluorescence,was employed to measure fuel plume morphology at various downstream locations under ambient temperature conditions.The results show that the expansive trailing edge significantly enhances the vertical diffusion of the fuel,leading to distinct plume characteristics.Compared to the strut injecting fuel into the edge of the streamwise vortex,the strut injecting fuel into the core of the streamwise vortex results in a larger fuel plume area with a more uniform distribution.Additionally,a streamwise vortex model was established to investigate the vortex dynamics and mixing mechanisms behind the strut from a mechanistic perspective.The simulation results indicate that the model demonstrates good performance in forecasting the dynamics of streamwise vortices and the evolution of fuel plume morphology.展开更多
基金supported by the National Natural Science Foundation of China(No.12002193)the Shandong Provincial Natural Science Foundation,China(No.ZR2019QA018).
文摘In this paper,some typical methods to promote mixing in supersonic combustion are reviewed,and the fluid-dynamic mechanism underpinning the development of the supersonic shear layer in the presence of a streamwise vortex is analyzed through computational fluid dynamics.It is proven that the streamwise vortex-couple method is an excellent approach to enhance mixing.A specific combustor design is proposed accordingly.
基金supported by the National Natural Science Foundation of China(Grants 11490551,11472154, 11132005,and 11322221)
文摘The generation of a hairpin vortex from near-wall streamwise vortices is studied via the direct numerical simulation（DNS） of the streak transient growth in the minimal channel flow at Re_τ- 400.The streak profile is obtained by conditionally averaging the DNS data of the fully developed turbulent channel flow at the same Reynolds number.The near-wall streamwise vortices are produced by the transient growth of the streak which is initially subjected to the sinuous perturbation of the spanwise velocity.It is shown that the arch head of the hairpin vortex first grows from the downstream end of the stronger streamwise vortex and then connects with the weaker,opposite-signed streamwise vortex in their overlap region,forming a complete individual hairpin structure.The vorticity transport along the vortex lines indicates that the strength increase and the spatial expansion of the arch head are due to the stretching and the turning of the vorticity vector,respectively.The hairpin packets could be further produced from the generated individual hairpin vortex following the parent-offspring process.
基金Project supported by the National Natural Science Foundation of China Nos.50476004 and 10732090)
文摘A mechanism for generation of near wall quasi-streamwise hairpin-like vortex （QHV） and secondary quasi-streamwise vortices （SQV） is presented. The conceptual model of resonant triad in the theory of hydrodynamic instability and direct numerical simulation of a turbulent boundary layer were applied to reveal the formation of QHV and SQV. The generation procedures and the characteristics of the vortex structures are obtained, which share some similarities with previous numerical simulations. The research using resonant triad conceptual model and numerical simulation provides a possibility for investigating and controling the vortex structures, which play a dominant role in the evolution of coherent structures in the near-wall region.
文摘How control in turbomachinery is very difficult because of the complexity of its fully 3-D flow structure. The authors propose to introduce streamwise vortices into the control of internal flows. A simple configuration of vortices was investigated in order to better understand the flow control methods by means of streamwise vortices. The research presented here concerns streamwise vortex interaction with a horseshoe vortex. The effects of such an interaction are significantly dependent on the relative location of the streamwise vortex in respect to the leading edge of the profile. The streamwise vortex is induced by an air jet. The horseshoe vortex is generated by the leading edge of a symmetric profile. Such a configuration gives possibility to investigate the interaction of these two vortices alone. The presented analysis is based on numerical simulations by means of N-S compressible solver with a two-equation turbulence model.
基金supported by the National Natural Science Foundation of China (No. 10772082)AFOSR(No. FA9550-08-1-0201)
文摘Formation and evolution of secondary streamwise vortices in the compressible transitional boundary layers over a flat plate are studied using a direct numerical simu- lation method with high-order accuracy and highly effective non-reflecting characteristic boundary conditions. Generation and development processes of the secondary streamwise vortices in the complicated transitional boundary flow are clearly analyzed based on the of numerical results, and the effects on the formation of the ring-like vortex that is vital to the boundary layer transition are explored. A new mechanism forming the ring-like vortex through the mutual effect of the primary and secondary streamwise vortices is expressed.
基金This study was supported by the National Science and Technology Major Project,China(No.J2019-III-0016-0060)。
文摘The mixing effectiveness of the airflow between the inner and outer bypass inlets of a Rear Variable-Area Bypass Injector(RVABI)is the key to the afterburner performance of variable cycle engines.This paper describes an optimized RVABI design based on an alternating area regulator to improve the velocity/temperature uniformity of the incoming flow at the afterburner.Compared with a classical RVABI,numerical simulations show that the proposed alternating RVABI performs better in terms of thermal mixing efficiency and total pressure loss in different variable cycle engine modes.Both the increasing air contact area between the inner and outer bypass of alternating structure RVABI,and a larger streamwise vortex in the inner bypass inlet due to the proposed alternating lobe structure in the RVABI contribute to the significantly increase of mixing effectiveness.Besides,the alternating regulator induces strong streamwise vortex,which helps to improve the airflow mixing with its vortex-induced velocity.The interaction between the streamwise vortex and azimuthal vortex further promises the velocity/temperature uniformity after the RVABI.With the increase of alternating lobe’s height ratio,the covering area of the streamwise vortex and the azimuthal vortex is enlarged,which further enhances the thermal mixing efficiency of the RVABI.This design gives an insight into the future design and optimization of RVABI.
文摘Turbulent spots play a key role in the formation of the turbulence and the transition. The generation and evolution of turbulent spots using the wall impulse model in the plane Couette flow are studied by direct numerical simulation of Navier-Stokes equations. A group of three-dimensional coupling compact difference schemes with high accuracy and high resolution is used in the numerical calculation. The important characteristics of turbulent spots based on the results of examples are analyzed, including the formation of random pulse, the generation of Reynolds stress, the growth of disturbance amplitude, and the continuous change of spot shape, especially the complex evolution process of the streamwise vortices. Computational results confirm that basic properties of turbulent spots in the laminar flow are similar to those in the turbulent flow.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51179134)the National Key Basic Research Program of China(Grant No.2014CB239203)Program for New Century Excellent Talents in University(Grant No.NCET-12-0424)
文摘The performance of an annular jet pump( AJP) is determined by its area ratio A( ratio of cross sectional area of throat and annular nozzle) and flow rate ratio q( ratio of primary and secondary flow rate,Qs/Qj),while the nozzle lip thickness is neglected in the present studies. This paper presents a study on the effect of the thickness on the flow field and performance of an AJP with A = 1. 75. With the increasing flow rate ratio and nozzle lip thickness,a small vortex forms at the nozzle lip and keeps on growing. However,as the flow rate ratio or nozzle lip thickness is extremely low,the vortex at the lip vanishes thoroughly. Moreover,the recirculation width varies conversely with the nozzle lip thickness when the flow rate ratio q ≤ 0. 13. While the deviation of the recirculation width with different nozzle lip thickness is negligible with q ≥ 0. 13. Additionally the existence of nozzle lip hinders the momentum exchange between the primary and secondary flow and leads to a mutation of velocity gradient near the nozzle exit,which shift the recirculation downstream. Finally,based on the numerical results of the streamwise and spanwise vortex distributions in the suction chamber, the characteristics of the mixing process and the main factors accounting for the AJP performance are clarified.
基金National Natural Science Foundation of China(51161130525)"111" Project (B08009)
文摘In order to investigate the effects of the airfoil-probes on the aerodynamic performance of an axial compressor,a numerical simulation of 3D flow field is performed in a 1.5-stage axial compressor with airfoil-probes installed at the stator leading-edge（LE）.The airfoil-probes have a negative influence on the compressor aerodynamic performance at all operating points.A streamwise vortex is induced by the airfoil-probe along both sides of the blade.At the mid-operating point,the vortex is notable along the pressure side and is relatively small along the suction side（SS）.At the near-stall point,the vortex is slightly suppressed in the pressure surface（PS）,but becomes remarkable in the suction side.A small local-separation is induced by the interactions between the vortex and the end-wall boundary layer in the corner region near the hub.That the positive pitch angle of the airfoil-probe at 6.5% span is about 15° plays an important role in the vortex evolution near the hub,which causes the fact that the airfoil-probe near the hub has the largest effects among the four airfoil-probes.In order to get a further understanding of the vortex evolution in the stator in the numerical simulation,a flow visualization experiment in a water tunnel is performed.The flow visualization results give a deep insight into the evolution of the vortex induced by the airfoil-probe.
基金supported by the National Science and Technology Major Project(No.J2019-Ⅲ-0001-0044)。
文摘The air-turbo-rocket(ATR)engine is a promising propulsion plant for achieving numerous surface and air launched missile missions.The application of lobed mixer in the ATR combustor can promote the mixing of the fuelrich gas and the air,thus improving the engine performance significantly.The numerical simulation method was conducted to explore the effects of lobe peak-to-trough width ratio on mixing and combustion performance in ATR combustors.Results show that:For a given peak lobe width b1,the combustion efficiency and total pressure loss decrease with the increase of trough lobe width b2;For a given b2,the combustion efficiency and total pressure loss decrease with the increase of b1;The fan-type lobed mixer with smaller b2has a better effect on promoting the combustion efficiency in the region near the ATR combustor center line than that with a pair of parallel side walls.The total pressure recovery coefficient reaches more than 0.99 at the exit of combustor in nonreactive combustion while the total pressure loss reaches more than 4%in the reacting combustion.Compared with the mixing process,more than80%of the total pressure loss is caused during combustion.
基金Project supported by the National Natural Science Foundation of China(Grant No.52176041)。
文摘In this study,the delayed detached eddy simulation(DDES)is coupled with a homogenous cavitation model to simulate the cavitating turbulent flow around a propeller behind a full body ship with special emphasis on the influence of the vortex generator(VG)on the propeller cavitation and the hull pressure fluctuation.The small calculation uncertainty as evaluated by the DDES verification and validation(V&V)method indicates that the present simulation can accurately reproduce the propeller performance and cavitation,and the predicted hull pressure fluctuation is in a fairly good agreement with the available experimental data.The mechanism is explored through the current numerical results how the VG affects the local velocity distribution,along with the influences of the VG on the propeller cavitation and the hull pressure fluctuation.It is shown that the streamwise vortex is induced by the VG near the hull boundary layer.The very low velocity region in the hull wake is reduced due to the effect of the streamwise vortex.Besides,the propeller cavitation develops more mildly and the hull pressure fluctuation decreases due to the influence of the VG.
文摘The alternating wedge strut,serving as both an injector and a vortex generator,has great potential for application in the scramjet combustor.The expansive trailing edge structure can further enhance the mixing performance of the alternating wedge strut.To enhance the performance of scramjet engines,it is essential to investigate the fuel/air mixing characteristics and mechanism downstream of alternating wedge struts with expansive trailing edges.The research focused on the impact of two different fuel injection schemes on the air/fuel mixing process and plume morphology.The optical diagnostic technique,particle laser-induced fluorescence,was employed to measure fuel plume morphology at various downstream locations under ambient temperature conditions.The results show that the expansive trailing edge significantly enhances the vertical diffusion of the fuel,leading to distinct plume characteristics.Compared to the strut injecting fuel into the edge of the streamwise vortex,the strut injecting fuel into the core of the streamwise vortex results in a larger fuel plume area with a more uniform distribution.Additionally,a streamwise vortex model was established to investigate the vortex dynamics and mixing mechanisms behind the strut from a mechanistic perspective.The simulation results indicate that the model demonstrates good performance in forecasting the dynamics of streamwise vortices and the evolution of fuel plume morphology.
