Modification of turbulence models for pressure-induced separation on smooth surfaces using the DLR VicToria experiment

Kurzfassung

A new experiment of a turbulent boundary layer flow at a large adverse pressure gradient at a high Reynolds number is presented. The strong pressure gradient leads to pressure-induced separation on the smooth surface of the geometry model with a thin separation bubble. The experiment was performed within the DLR internal project VicToria. First, the design of the test case, the set-up in the wind tunnel, and the measurement technique using both large-scale and high-magnification particle imaging and Lagrangian particle tracking are described. Then the experimental results for the mean velocity are described as the flow evolves downstream from the zero-pressure gradient region into the adverse pressure gradient region. From the measurement data a wall law for the mean velocity with a thin log-law region and a half-power law region above the log-law is observed in the adverse pressure gradient region. Then the differential Reynolds stress transport model SSG/LRR-omega is considered. Based on the observation that the length-scale equation is not consistent with the assumed wall laws at adverse-pressure gradient, a modification of the equation for the dissipation rate omega in the model is proposed, so that the modified model can predict the observed wall law at adverse-pressure gradient. Finally, the numerical results using the modified SSG/LRR-omega model are shown. The modification causes a reduction of the mean velocity in the inner part of the boundary layer at adverse-pressure gradients, making the modified model more susceptible for flow separation. The numerical predictions of the modified model are found to be in good agreement with the experimental data.