Small-scale roughness elements or imperfections are inevitable over the surface of a flight vehicle.The aerodynamics of these small-scale structures is difficult to predict but may play an important role in the design...Small-scale roughness elements or imperfections are inevitable over the surface of a flight vehicle.The aerodynamics of these small-scale structures is difficult to predict but may play an important role in the design of a flight vehicle at high speed.The forward-facing step is a typical type of roughness element.Many experiments have been conducted to study the aerodynamics of supersonic forward-facing step,especially with a step height larger than boundary layer thickness.However,few studies focus on small steps.To improve the understanding of small-scale forwardfacing step flow,we perform a series of simulations to analyze its aerodynamic influence on a Mach number 5 turbulent boundary layer.The general flow structures are analyzed and discussed.Several shock waves can be induced by the step even if the step height is much smaller than the boundary layer thickness.Two significant shocks are the separation shock and the reattachment shock.The influenced area by the step is limited.With the increase of the step height,the non-dimensional influence area decreases and gradually converges when the step height reaches the boundary layer thickness.There are two normalized distributions of the skin friction coefficient and pressure coefficient associated with step height.By using the normalized parameters,a power-law relationship between the step height and the drag increment coefficient is revealed and fits the simulation results well.It is further illustrated that this relationship still holds when changing the inlet angle of attack,but needs slight modification with the angle of attack.展开更多
The experimental investigation is conducted with LDV and hydrogen bubble technique in water flow. The shear layer thickness. the vorticity thickness. the maximulll value of turbulence intensities. the turbulent coher...The experimental investigation is conducted with LDV and hydrogen bubble technique in water flow. The shear layer thickness. the vorticity thickness. the maximulll value of turbulence intensities. the turbulent coherent structure. the variations of wall shear stress and the boundary layer shape factor are obtained. In the redevelopment region. the detailed analysis is first made for the streak structures in the near wall region and the turbulent boundary layer is formed at (x-xr) / h = 20.展开更多
Shock wave/boundary layer interaction(SWBLI)is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles.Supersonic forward-facing step(FFS),an extreme case of compression ...Shock wave/boundary layer interaction(SWBLI)is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles.Supersonic forward-facing step(FFS),an extreme case of compression ramp,often occurs severe SWBLIs with a large separation bubble.In this paper,experimental investigations on vortical structures and density fluctuations characteristics of supersonic FFS controlled by self-sustaining dual synthetic jets(SDSJ)are carried out in a Mach number 2.95 wind tunnel.High spatial–temporal resolution flowfield images of FFS without/with active flow control are captured by adopting nano-particle-based planar laser scattering technique.The control effects of the distance between the actuator and the step are mainly compared.The paper finds that the SDSJ can effectively change the feature of flowfield,eliminate the separation shock and the reattachment shock,compel the original shock induced by the step leading edge to distort and reduce its intensity finally.Density fluctuations analysis demonstrates that the whole flows seem to move upstream with the increase of distance(dS-J).Discrete Fourier transformation spectrums results reveal that the fluctuations are mainly located in the low-frequency region at first.High-frequency components and frequency bandwidth increase slightly after the SDSJ are applied.展开更多
A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the...A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.展开更多
基金financial support from the National Natural Science Foundation of China(Nos.11602127 and 11572176)。
文摘Small-scale roughness elements or imperfections are inevitable over the surface of a flight vehicle.The aerodynamics of these small-scale structures is difficult to predict but may play an important role in the design of a flight vehicle at high speed.The forward-facing step is a typical type of roughness element.Many experiments have been conducted to study the aerodynamics of supersonic forward-facing step,especially with a step height larger than boundary layer thickness.However,few studies focus on small steps.To improve the understanding of small-scale forwardfacing step flow,we perform a series of simulations to analyze its aerodynamic influence on a Mach number 5 turbulent boundary layer.The general flow structures are analyzed and discussed.Several shock waves can be induced by the step even if the step height is much smaller than the boundary layer thickness.Two significant shocks are the separation shock and the reattachment shock.The influenced area by the step is limited.With the increase of the step height,the non-dimensional influence area decreases and gradually converges when the step height reaches the boundary layer thickness.There are two normalized distributions of the skin friction coefficient and pressure coefficient associated with step height.By using the normalized parameters,a power-law relationship between the step height and the drag increment coefficient is revealed and fits the simulation results well.It is further illustrated that this relationship still holds when changing the inlet angle of attack,but needs slight modification with the angle of attack.
文摘The experimental investigation is conducted with LDV and hydrogen bubble technique in water flow. The shear layer thickness. the vorticity thickness. the maximulll value of turbulence intensities. the turbulent coherent structure. the variations of wall shear stress and the boundary layer shape factor are obtained. In the redevelopment region. the detailed analysis is first made for the streak structures in the near wall region and the turbulent boundary layer is formed at (x-xr) / h = 20.
基金The present research was supported by the National Natural Science Foundation of China(Grants 11972369,51809271,11872374 and 11602299).
文摘Shock wave/boundary layer interaction(SWBLI)is still one of the unresolved bottlenecks that restrict the development of more advanced flight vehicles.Supersonic forward-facing step(FFS),an extreme case of compression ramp,often occurs severe SWBLIs with a large separation bubble.In this paper,experimental investigations on vortical structures and density fluctuations characteristics of supersonic FFS controlled by self-sustaining dual synthetic jets(SDSJ)are carried out in a Mach number 2.95 wind tunnel.High spatial–temporal resolution flowfield images of FFS without/with active flow control are captured by adopting nano-particle-based planar laser scattering technique.The control effects of the distance between the actuator and the step are mainly compared.The paper finds that the SDSJ can effectively change the feature of flowfield,eliminate the separation shock and the reattachment shock,compel the original shock induced by the step leading edge to distort and reduce its intensity finally.Density fluctuations analysis demonstrates that the whole flows seem to move upstream with the increase of distance(dS-J).Discrete Fourier transformation spectrums results reveal that the fluctuations are mainly located in the low-frequency region at first.High-frequency components and frequency bandwidth increase slightly after the SDSJ are applied.
文摘A forward-facing step (FFS) immersed in a subsonic boundary layer is studied through a high-order flux reconstruction (FR) method to highlight the flow transition induced by the step. The step height is a third of the local boundary-layer thickness. The Reynolds number based on the step height is 720. Inlet disturbances are introduced giving rise to streamwise vortices upstream of the step. It is observed that these small-scale streamwise structures interact with the step and hairpin vortices are quickly developed after the step leading to flow transition in the boundary layer.
