Roughness Modeling for Turbomachinery

Fundamental concepts for roughness modeling have been further explored and advanced. A basic understanding of the effect of distributed roughness on fully developed turbulent boundary layer, its possible influence on transition, and the mechanism of local spanwise roughness on transition has been achieved. Predictions with a refinement around a spanwise roughness element have been conducted in comparison to TATMo’s turbine cascade investigated at VKI. 3d-computations document the status in comparison to the T106C measurements with spanwise roughness for all Reynolds-numbers with two different transition models. Additional validation work shows the reproduction of accurate behavior of influence of height, location, and shape of the roughness element on pitchwise averaged loss and exit angle at midspan. Beside the correct reproduction of flow quantities for the spanwise roughness element, the right assessment of distributed roughness on surfaces of an industrial configuration is important. Because a high grid resolution very near the wall on all surfaces is not always possible, the problem can be solved with the help of wall-functions. The results of the application document the significance of rough wall-function modeling for tubomachinery.Copyright © 2011 by ASME