Durbin楕円緩和モデルに基づく応力方程式モデルの自由表面乱流への適用性について

抄録

The elliptic relaxation model of Durbin [J. Fluid Mech., 249 (1993) 465], which has had remarkable success in predicting wide variety of flows, is applied to prediction of free-surface turbulence for the first time. A set of appropriate free-surface boundary conditions for the elliptic relaxation equations is derived by taking account of the balance of dominant terms in the Reynolds-stress transport equations in the vicinity of a free surface. Test calculations for a fully-developed turbulent open-channel flow is conducted. The flow consists of two kinds of impermeable boundaries, a solid wall and a free surface, and hence is quite suitable to the present benchmark flow. It is demonstrated that the proposed boundary conditions do enable elliptic relaxation models to reproduce the correct surface-induced stress anisotropy and that the model properly describes the differences in feature between wall-bounded flows and free-surface flows by its main quality in reproducing the non-local blocking effect, kind of an elementary process of boundary-turbulence interaction. It is also found that the turbulent-transport term plays a central role in characterizing free-surface turbulence, which is therefore quite suitable for critical evaluation of the model performance.