Hypersonic Flow Field Response And Boundary Layer Susceptibility Induced By Roughness Element

Hypersonic boundary layer transition will directly affect the flight control,propulsion,thermal protection and other aspects of hypersonic vehicles.Therefore,it is necessary to study the transition of hypersonic boundary layer.The first stage and inevitable stage of hypersonic boundary layer transition are called receptivity.Receptivity refers to the response stage of the boundary layer to the external disturbance,in which the disturbance wave in the boundary layer is excited by the external disturbance and propagates to the downstream.The study of receptivity is the basis of revealing the mechanism of boundary layer transition.The receptivity is affected by many factors,including freestream disturbance and wall disturbance.The influence of freestream disturbance on the receptivity of boundary layer has been studied by theoretical,experimental and numerical simulation methods.The wall disturbance has a more direct effect on the flow structure in the boundary layer and has a significant effect on the receptivity of the boundary layer.The existing research shows that the wall roughness can play an important role in the drag reduction and heat reduction of hypersonic vehicles,and the boundary layer becomes more stable.However,the transition mechanism of the hypersonic boundary layer under the action of various disturbances has not been clarified,which needs to be further studied.Therefore,this paper takes the wall roughness as the research object,mainly studies the excitation and evolution process of the disturbance wave in the lower boundary layer for the freestream disturbance action of the wall roughness.The time term,viscosity term and convection term are discretized by using the high order accurate finite difference scheme.Specifically,the three-step three-step TVD Runge Kutta scheme is used for time advancement.The S-W flux vector splitting method is used to split the convection term into positive and negative flux terms,and then the five step WENO scheme is used to discrete the positive and negative flux terms after splitting.The viscous term is discretized by the sixth order central difference scheme.The numerical simulation of hypersonic flow around a blunt cone is carried out by using high-order precision finite difference method.The influence of wall roughness(distributed roughness)on the flow structure in hypersonic steady flow field is analyzed,and the influence of smooth wall and roughness wall on hypersonic flow field and boundary layer is compared.The freestream slow acoustic waves is introduced into the hypersonic steady flow field.The influence of the freestream slow acoustic waves on the hypersonic flow field and the flow structure in the boundary layer is analyzed.The propagation process of the freestream slow acoustic waves disturbance in the boundary layer is revealed.The mechanism of the evolution of the disturbance waves with different modes in the boundary layer is studied by the fast Fourier transform method.Based on the action mechanism of wall roughness on hypersonic steady flow-field and freestream disturbance on unsteady flow-field under the action of wall roughness,the action mechanism of wall roughness on hypersonic steady flow field under different wall temperature conditions(T_W=200K,450K,650K,850K)is considered,and the excitation and evolution of the disturbance wave in the boundary layer under the action of the freestream slow acoustic waves by the wall roughness.The influence of wall roughness on the propagation process of different modes of disturbance waves in the boundary layer is studied.