MODELING THE EFFECTS OF STEPS ON BOUNDARY-LAYER TRANSITION

An experimental and computational study is conducted to develop a model for the effects of surface steps on transition to turbulence in boundary layers. The step effects are captured within the framework of a variable n-factor method, where the step results in a reduction in the TS-wave transition n-factor NTS. Data is presented for NTS for favorable and adverse pressure gradients. Backward-facing steps result in significantly larger reductions in the transition n-factor when compared to forward-facing steps. The results show that step effects can be accounted for by using a NTS for step heights up to 1.5 times the local boundary-layer displacement thickness.