Partially Averaged Navier Stokes simulations of flow around simplified train geometries with passive control devices to reduce aerodynamic drag

Abstract

Saving energy has gained an increased importance both for economical and environmental reasons. For trains, the lowering of the aerodynamic drag is an important aspect for energy efficiency. A strategy is to use passive control devices that interact with the flow and thereby reduces the drag. The purpose of the present thesis has been to evaluate the drag reducing effects of two different passive control devices, namely vortex generators and corner nozzles. The aerodynamic drag is partly developed from skin friction on the surface and partly from the pressure difference between the front and rear end of a train. The focus in this thesis has been on reducing the pressure difference. The evaluation was performed using Computational Fluid Dynamics (CFD) with PANS to simulate the flow around train models. The simulations were done on three different cases; one for a simple train model without control devices, one for a train model with vortex generators and one for a train model with corner nozzles attached. The dimensions of the train model were chosen similar to a previous wind tunnel study, which was also used for comparison of the results. The Reynolds number used in the simulations was 50,000, significantly lower than in the experiments, due to the demanded computational time and computer power. From the simulation results there was an increase in pressure behind the train in the wake when using both control devices, but it was no decrease in CD for the total train geometry including devices. The CD value for the vortex generators and corner nozzles were increased 11.2% and 0.4% respectively. With no regard to the CD part from the devices, the corner nozzles lowered the CD value of the train by 9% and the vortex generators by 0.1%