On the turbulence models and turbulent Schmidt number in simulating stratified flows

Abstract

Stratified flows are prevalent in indoor and outdoor environments. To predict these flows, this investigation evaluated the performance of seven turbulence models by comparing the simulation results with the experimental data of both weakly and strongly stratified jets. The models tested included six Reynolds-averaged Navier-Stokes models and one large eddy simulation (LES) model. The velocity, turbulent kinetic energy (TKE), and Reynolds stress distributions were examined. For the weakly stratified jet, all seven models could predict well the mean velocity, but for the strongly stratified jet, the Reynolds stress model and LES models overpredicted the velocity in the unstable stratification region. The Shear Stress Transport (SST) k − ω model was the best. This paper also introduced a new dynamic turbulent Schmidt number model which can improve the prediction of density distribution. In addition, this investigation analysed the computing costs of the models as well as the vorticity and entrainment ratios predicted by the models.

On the Values for the Turbulent Schmidt Number in Environmental Flows

“…A linear relationship between Sc t and Ri was proposed, in which Sc t increased with the increasing level of stratification, i.e., with Ri [50,54]. Even, Shi et al [72] noted that the larger the value of Sc t was, the higher the predicted peak density was. This is because the mixing of the two species in the stratified flows was inversely dependent on Sc t .…”

“…Furthermore, some of the presented studies suggested that Sc t should be considered as a parameter, which has different values in the same flow domain, but there was no agreement about the parameters controlling this variability in the flow domain. In sediment transport, some studies suggested even an influence of the presence or not of bedforms [41] and of the type of transported particles [43,48], whereas in stratified flow, even the effect of density gradients was observed [50,54,72].…”

“…Shi et al [72] Density stratified jets Exp/Num − Sc t = Sc t (velocity and density gradient) Koeltzsch [66] reviewed some previous experimental investigations and found that most authors use a constant value for Sc t ranging from 0.5 to 0.9.…”

“…Shi et al [72] investigated the performances of six RANS models and one LES model in predicting both weakly-and strongly-stratified jets. The velocity, turbulent kinetic energy and Reynolds stress distributions were examined.…”

“…A second group of studies investigated the question if Sct is a constant or it is varying inside the flow domain [66,[70][71][72]. Koeltzsch [66] carried out wind tunnel experiments in a turbulent boundary layer above a flat plate.…”