Prediction of turbulent skin friction for two-dimensional, rib-type surface roughness using a discrete element approach

A discrete element model for turbulent flow over two-dimensional rib-type roughness is developed and validated. Surface roughness blockage effects and form drag are included as a constituent part of the differential equations. Separation and reattachment of the flow over rib roughness are identified as the dominant flow phenomena, and models are developed which incorporate the separated region geometry into the blockage. The form drag model is based on the pressure difference between the windward and leeward forces of the roughness. Predictions are compared with a variety of data sets. These comparisons indicate that the discrete element approach can be successfully applied for rib-type roughness. However, the model has a more narrow range of application for different surface geometries than the very broad range which has previously been demonstrated for three-dimensional, distributed roughness.