Effect Of Rectangular Cavity On The Flow Stability In A Hypersonic Boundary Layer On A Blunt Flat Plate

A cavity inevitably exists in the surface of a ablation wall with reticular fillers of thermal protection system in a high-speed aerocraft and its joint.The existence of cavity will affect its flow stability.In this paper,a hypersonic boundary layer on a blunt flat plate with Mach number 6 was chosen as the research object.By combining linear stability theory(LST),direct numerical simulation(DNS)and Bi-global stability analysis(Bi-Global),the effect of rectangular cavities on the flow stability and transition was quantitatively described by the N-value correction of ?N(?,h,w).The effects of depth,width,position,combination spacing of 2D rectangular cavities,and the length,width,depth of 3D rectangular cavities on the flow stability and transition were analysed.Conclusions obtained through numerical simulation results for different conditions include:1.The effect of a rectangular cavity on the base flow is local.A stable,closed and ringlike vortex structure appears in the cavity,whose form is closely related to the width-depth ratio of the cavity.2.The N-value correction N is defined as ?N(?,h,W)to quantitatively describe the effect of a rectangular cavity with depth h and width w on the stability and transition of a disturbance wave with a fixed frequency ?,through which engineers can quickly and effectively predict the transition position for the cases with rectangular cavities.3.A 2D rectangular cavity can suppress disturbance waves of various frequencies,and the suppression of a disturbance wave with a fixed frequency increases with the increase of width and depth of the cavity.When the depth and width of the cavity are large enough,the flow after it shows obvious periodicity.As the position of a rectangular cavity moves backward,its suppression of a disturbance wave tends to decrease linearly.The combined rectangular cavities have the same suppression effect of a disturbance wave as the superposition effect of two cavities acting separately.4.A 3D transverse cavity can cause weak 3D characteristics of the base flow,and has the same effect as that of a 2D cavity on the stability of a boundary layer flow.In a 3D longitudinal cavity,the length-depth ratio is the key parameter to induce transition,while the width-depth ratio has weak effect on the induction of transition.Transition can be induced only when the length-depth ratio of a 3D transverse cavity is moderate.