流れ解析のための不規則粗面のモデル化(流体工学,流体機械)

概要

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A new idea is proposed in this work to convert an original rough surface of irregularly indented complex geometry to a simplified model surface. The purpose is to provide a substitutive simple solid boundary surface that allows us to perform a RANS by a practical computer of ordinary memory size and computational speed. As tall and comparatively large roughness peaks are expected to affect dominantly the flow over an irregularly indented surface, it is intended here to pick up those peaks adequately and substitute them by equivalent hemispheres. The first task is to coarsen the original surface to remove surface indentation of high frequency. In place of filtering the surface by a filtering function as is common in LES, wavelet multi-resolution analysis is introduced. Specifying a threshold height on the coarsened surface, we obtain a map of islands of peaks taller than the threshold plane. These peaks are converted to hemispheres of same volume. Hemispheres are least sensitive with respect to interference with surrounding elements and individual hydrodynamic performance is most easily evaluated. Wall drag of channel flows having original and model surfaces are compared by RANS simulation and has been confirmed to be coincident with reasonable accuracy.
2007-05-25