Investigation of machining flaw of transverse micro-grooves on the control effect of boundary layer instability

Local machining flaw of transverse rectangular micro-grooves is investigated from the viewpoint of suppressing the second mode disturbances of a hypersonic boundary layer. The effect of local deformed micro-grooves on boundary layer stability was studied by the direct numerical simulation (DNS) where the second mode disturbances are imposed to the base flow of the boundary layer. The results showed that compression waves and expansion waves were generated on the surface of the deformed micro-groove. Micro-scale separation bubbles may appear at the rear edge of the deformed micro-grooves. The results show that the local deformation of micro-grooves is more effective in suppressing the second mode waves than the corresponding regular one. With the increase of the deformation height, the suppressing effect becomes great. Compared with the regular rectangular micro-grooves, the amplitude inhibition rate of the local deformation micro-grooves to the second mode disturbance can reach 19.6%.