Modeling Distributed Roughness Using Effective Surfaces

Abstract

How laminar flow interacts with distributed roughness has yet to be described in a cohesive fashion. To advance theoretical efforts, a preliminary model inspired by experimental results is proposed here and evaluated. Significant evidence suggests distributed roughness fields generate a ‘shielding’ effect that reduces the impact of individual roughness elements on the flow. One way to model shielding is to create an effective surface which reduces the apparent height of the roughness elements. In this thesis, possible effective surfaces are coupled with different wall boundary conditions. These are analyzed using triple-deck theory. The results are examined for their effectiveness at reproducing results from a full distributed roughness configuration. Results from this effort have discounted no-shear as a possible boundary condition. Furthermore, a simplified imposed-slip velocity model demonstrates the strong dependence of the model’s success upon matching actual in-plane velocity values where the effective surface replaces the control geometry.