effect of pressure gradient on local excitation of boundary-layer instability due to free-stream turbulence and micro surface roughness

The prediction and control of the laminar-turbulent transition is crucial to the designs of vehicles, turbines, etc. the initial condition of transition depends on the exciting process of boundary-layer instability, which is the key to implement its prediction and control. the current researches confirm that the exciting process of boundary-layer instability, namely receptivity, is affected not only by different types of free-stream disturbances and shape parameters of surface roughness elements, but also by the pressure gradient of mean flow. hence, we study the effect of pressure-gradient on local excitation of boundary-layer instability under the interaction of the low-level, isotropic free-stream turbulence and micro surface roughness in this work. the numerical results reveal the pressure-gradient effect on the receptive process and the group speed of excited wave packets in the falkner-skan boundary layer. the favorable/adverse pressure gradients (fpg/apg) are found to be able to promote/suppress the excitation and subsequent evolution of tollmien–schlichting (t-s) waves. then the relations of the pressure gradient with the amplitude, growth rate, wave number, phase speed and shape function of excited t-s waves are studied.