Parameter Effects of Spanwise-arrayed Cylindrical Roughness Elements on Transition in the Falkner-Skan-Cooke Boundary Layer

The effects of roughness parameters, including height, diameter, and spacing the cylindrical elements, on turbulent transition are investigated in a three-dimensional boundary layer using direct numerical simulation. There two types process, classified as gradual forced. former is caused by linear development crossflow vortices their secondary instability, while latter an immediate breakdown to turbulence behind without any vortex. These processes only demarcated height. diameter affect initial creation vortex well onset instability transition. With fixed volume, greater height induces larger disturbances causes earlier than diameter. aforementioned observations apply when most unstable mode induced. When absent or secondarily induced, disturbance decays point shifts downstream. Therefore, considering critical parameter between forced transitions, crucial. However, for transition, parameters we should consider flow alternation roughness.