Abstract
A model for an irregularly indented rough surface has been proposed by the authors in which tall peaks are picked up and represented by hemispheres having equal volume with each concerned peak. In practical application, drag of hemispheres are substituted by plane shear stress on a flat plate. This simplified model surface is used to simulate flow over the original rough surface. The model requires drag of a hemisphere on a flat plate. In this work, appropriate formula for the drag which is simple and acceptably accurate in balance with the compactness of the model, is deduced by numerical simulations. Channel flows having periodically arranged hemispheres on both plates are simulated using two-equation turbulence model. Obtained drag form is confirmed to compare reasonably with those realized by hemispheres of different size and in different situation, in a flow equipped with the model rough surface. The form is applied also to pipe flows having periodic hemispheres on the wall and is found to reproduce measured friction. Although the proposed idea must be examined more carefully and improved in details, promising step has been set up to make proposed model an important method in practical application.
