COMPARING THE PERFORMANCE OF THE MELLOR-YAMADA AND THE K-EPSILON 2-EQUATION TURBULENCE MODELS

The aim of this paper is to systematically compare k-epsilon and Mello r-Yamada two-equation turbulence models. Both models include prognosti c equations for turbulent kinetic energy and a length scale related pa rameter which are used to calculate eddy viscosities and vertical diff usivities. The results from laboratory experiments, using mixed and st ratified flows, are simulated in order to systematically compare and c alibrate the models. It is shown that the Monin-Obukhov similarity the ory is well represented in both models. The models are used to simulat e stratified tidal flow in the Irish Sea, and the results show that th e k-epsilon models generally predict a larger phase lag between curren ts and turbulent dissipation, in the bottom boundary layer, than the M ellor-Yamada models. The comparison between the model results and fiel d measurements, of the rate of dissipation of turbulent kinetic energy , shows that both models require modification through the inclusion of an internal wave parameterization in order that they are able to corr ectly predict the observed levels of turbulent dissipation. As the mai n result, it is shown that the choice of the stability functions, whic h are used as proportionality factors for calculating the eddy viscosi ty and diffusivity, has a stronger influence on the performance of the turbulence model than does the choice of length scale related equatio n.