Evaluation of Algebraic Stress Modeling in Free-Surface Jet Flows

Abstract

This study evaluated three algebraic stress models for predicting turbulent stresses near the free surface in a free-surface jet at nonzero Froude number, by comparing to experiments. The models examined included one with no explicit near-surface modeling, one which specified model coefficients in terms of invariants of the anisotropy tensor, and a third model which employed a surface correction with an ad-hoc damping function. Experiment showed that at low Froude number, the anisotropy near the free surface did not attain the limiting behavior characteristic of two-dimensional turbulence and the anisotropy increased with streamwise distance. At high Froude number the surface can have little effect on the anisotropy. Far from the free surface, all the models performed well. For the model with no explicit free-surface modeling, the turbulence near the free surface was predicted to be isotropic. For the “anisotropy-invariant” model, the predicted anisotropy was too small and confined to locations too near the free surface. The model with the ad-hoc damping function captured the anisotropy near the free surface best, but specification of the decay constant in the damping function is an open question.