Control of first-mode oblique breakdown in a supersonic boundary layer using micro-groove coating strips

This paper describes a method for controlling the first-mode oblique breakdown in a Mach 2.0 supersonic boundary layer using micro-groove coating strips. The analysis is performed using the nonlinear parabolized stability equations. Micro-groove coating strips with various combinations of the groove half-width, porosity coefficient, and strip width are placed at different streamwise locations to control the transition. The results show that the micro-groove coating strip significantly suppresses the first-mode oblique breakdown. This effect is enhanced as the groove half-width, porosity coefficient, and strip width increase. When the micro-groove coating strip is located in the linear development region of the oblique breakdown, the suppression effect comes from the stabilization of the fundamental oblique mode by the micro-groove coating. When the strip is employed in the early nonlinear or late nonlinear development regions, a second stabilization mechanism, in addition to the stabilization effect of the micro-groove coating strip, is produced by the high-spanwise-wavenumber steady modes. Compared with the stabilization effect of the micro-groove coating strip, the second stabilization effect is more effective. The combination of these two stabilization mechanisms pushes the breakdown farther downstream.