On the modeling of roughness effects on the transition of von Kármán boundary-layer flow

Abstract Laminar-turbulent boundary-layer transition over rough rotating disks is addressed by means of linear-stability analysis. Computational data from two frequently used roughness-modeling approaches are obtained as input data for the stability analysis. It is demonstrated that the data arising from the two different approaches are not compatible with each other. Nevertheless, the stability analysis predicts postponed transition for both approaches. Two main conclusions emerge. Firstly, a theoretical study is required to establish which particular characteristics of the input data set result in the linear-stability analysis predicting postponed transition. Secondly, to guide future simulations an experimental study is essential to determine which one of the roughness-modeling approaches, if either, can produce data in agreement with measurements.