Study On The Susceptibility Mechanism Of Hypersonic Blunt Cone Boundary Layer Under Independent Rough Element Conditions

Laminar flow-turbulence transition of hypersonic boundary layer will lead to the change of hypersonic boundary layer state,which directly affects the performance of hypersonic aircraft in flight control,propulsion,thermal protection and other aspects.Therefore,it is very necessary that the study of hypersonic boundary layer transition mechanism for the development of hypersonic aircraft.As the initial stage of transition of hypersonic boundary layer,sensitivity refers to the process of excitation and evolution of disturbance waves in the boundary layer caused by external disturbance,which directly determines the initial conditions of transition of boundary layer,therefore,receptivity research is a joint to reveal the mechanism of transition of laminar flow and turbulence.The receptivity of the boundary layer is affected by a variety of exogenous disturbance factors,which can be mainly divided into freestream and wall disturbance,both of which will induce boundary layer transition.In the actual flight process of hypersonic aircraft,it is affected by a variety of disturbance factors,and the mechanism of hypersonic boundary layer transition under the coupling effect of various disturbance forms is still a subject to be studied deeply and systematically,therefore,this paper investigates the excitation and evolution process of disturbances in boundary layer as well as wall temperature effect in the receptivity of the boundary layer under the freestream disturbances and roughness element,mainly including the following aspects:(1)A high-order precision finite difference method is introduced to directly solve the two-dimensional conservative Navier-Stokes equations(N-S equations)to simulate the unsteady hypersonic flow field.Stger-Warming flux vector splitting method is used to split the convection term into positive and negative flux terms,then the fifth order WENO scheme is adopted to discretize the positive and negative flux terms.and a three-step and three-order TVD Runger-Kutta scheme is adopted to push forward the time term.At the same time,the viscous term is discretized by the sixth order central difference scheme.Finally verify the effectiveness of the proposed numerical method and determined the calculation model and boundary conditions.(2)The hypersonic blunt cone flow field is simulated by using the above-mentioned high-order precision finite difference method,by the floe characteristics such as the pressure,density,velocity and temperature to study the characteristics of flow filed,and the aerodynamic and thermodynamic characteristics of hypersonic flow field were studied by analyzing the parameters such as friction coefficient and the wall heat flux density,and the effects of independent roughness element on hypersonic flow field and boundary layer receptivity are discussed.(3)Furthermore,the continuous slow acoustic wave disturbance is introduced into the hypersonic flow field,the response of hypersonic flow field and the evolution of boundary layer disturbance wave are analyzed under the perturbation of the continuous slow acoustic wave and independent roughness element.The modal evolution of disturbance waves in the boundary layer is discussed by using Fourier spectrum analysis method,and the response characteristics to hypersonic flow field as well as the boundary layer receptivity under independent roughness element condition and smooth wall condition are compared and analyzed.The influences of independent roughness element on the receptivity of hypersonic boundary layer under the perturbation of the continuous slow acoustic wave are revealed.(4)Based on the effect of independent roughness element and the continuous slow acoustic wave disturbance on the hypersonic flow field,the action mechanism of the continuous slow acoustic wave on hypersonic steady flow field under different wall temperature conditions(T_w=200K,T_w=450K,T_w=650K,T_w=850K)is considered.The generation and evolution of disturbance waves in the boundary layer under the condition of independent roughness element are analyzed,especially,the wall temperature effect of hypersonic boundary layer under the perturbation of the continuous slow acoustic wave and independent roughness element is analyzed.