Numerical modeling of wind induced turbulent mixing processes in stratified water bodies

Abstract

The present work reports results of the numerical simulation of wind-induced mixing processes in stably stratified fluids using a two-equation k-ε closure model. Results reported are limited to the case of onedimensional, zero-pressure gradient flow, corresponding to water bodies of a longitudinal extension that is either very large or very small compared to the depth. Experimental observations provide a benchmark for the verification of the model at relatively low Richardson numbers. Turbulent mixing processes at higher Richardson numbers were also studied from the results of the numerical experiments, with the additional advantage over the laboratory ones of eliminating scale effects. Dimensionless entrainment rates as a function of the Richardson number were estimated, both for water bodies with a two-layer density profile as well as for linear density distributions. These results suggest a common entrainment relationship in both cases. Further analyses of the results from the numerical simulations show a great similarity in the characteristics of the turbulent structure of the mixed layer for both types of stratification, which would explain the apparent universality found for the entrainment law.