Stable stratification effects on the flow past surface obstructions: A numerical study

Abstract

Numerical predictions of the stably stratified flow fields past surface-mounted obstructions are presented. The time-averaged Reynolds equations, coupled with the continuity and temperature/concentration equation for the incompressible fluid, have been solved in the transformed space, using finite differences, adopting the Boussinesq approximation to account for density variations. Buoyancy effects on turbulence have been considered in the two-equation k-ε model, which has been used as a turbulence closure. The turbulent flow fields over a two-dimensional fence and around a three-dimensional hill were simulated for neutral and various stable conditions. The decrease of the cavity wake length behind the two-dimensional fence, due to the temperature gradient, was clearly depicted by the computations. The stability effect on the mean flow past the three-dimensional axisymmetric hill, for various Froude numbers, were reproduced satisfactorily, although some underestimation of the bouyancy influences in some cases was observed. The boundary layer lee side separation was suppressed with increasing stability, and the beginning of a hydraulic jump was predicted for Froude numbers smaller than unit. The comparison between the computations and the available measurements established the reliability of the presented method.