Vortical structures and density fluctuations analysis of supersonic forward-facing step controlled by self-sustaining dual synthetic jets

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.

Investigation of thermal protection system by forward-facing cavity and opposing jet combinatorial configuration

This paper focuses on the usage of the forward-facing cavity and opposing jet combinatorial configuration as the thermal protection system （TPS） for hypersonic vehicles. A hemispherecone nose-tip with the combinatorial configuration is investigated numerically in hypersonic free stream. Some numerical results are validated by experiments. The flow field parameters, aerodynamic force and surface heat flux distribution are obtained. The influence of the opposing jet stagnation pressure on cooling efficiency of the combinatorial TPS is discussed. The detailed numerical results show that the aerodynamic heating is reduced remarkably by the combinatorial system. The recirculation region plays a pivotal role for the reduction of heat flux. The larger the stagnation pressure of opposing jet is, the more the heating reduction is. This kind of combinatorial system is suitable to be the TPS for the high-speed vehicles which need long-range and long time flight.

Drag increment induced by a small-scale forward-facing step in Mach number5 turbulent boundary layer flows

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.

A survey on numerical simulations of drag and heat reduction mechanism in supersonic/hypersonic flows

Along with the survey on experimental investigations drawing attention to the drag and heat reduction mechanism, the authors simultaneously focus on the recent advances of numerical simulations on the schemes applied to supersonic/hypersonic vehicles. The CFD study has evolved as an irreplaceable method in scheme evaluation and aircraft optimization. Similar to our previous experimental survey, the advances in drag and heat reduction schemes are reviewed by similar kinds of mechanism in this article, namely the forward-facing cavity, the opposing jet, the aerospike, the energy deposition and their combinational configurations. This review article puts an emphatic eye on the flow conditions, numerical methods, novel schemes and analytical conclusions given in the simulations. Further, the multi-objective design optimization concept has also been illustrated due to the observable advantages of using CFD over experimental method, especially those performances conducted in drag reduction and thermal protection practice, and this would possess reference value in the design of aircraft system.