Development of Turbulence Models for Free-Surface Flows

Abstract

Abstract : The goal of this effort was to improve the ability to predict the free-surface flow in the near field of surface ships. The specific objectives were: to develop modeling approaches appropriate to the near-surface region in turbulent free surface flows and to obtain data for validation of CFD predictions of free-surface turbulent flows. The main results of this study can be summarized as follows: (1) The framework outlined in Hong & Walker (2000) was shown to be reasonable for turbulent free-surface flows. (2) The surface current is caused by a combination of turbulent surface fluctuations and turbulence anisotropy, with surface fluctuations dominating in high-Froude-number flows, and anisotropy otherwise. (3) The surface fluctuation effects can be approximated by a stress boundary condition. (4) A computational approach for predicting turbulence-generated waves was developed and the results compared favorably to experimental data. (5) Surface fluctuation measurements were carried out for a free-surface jet flow and the p.d.f. for the surface elevation was shown to be relatively Gaussian. (6) A method for measurement of the directional wave spectrum was developed and implemented and the directional spectrum of turbulence generated waves was characterized for a free-surface jet.