Computational Studies of Passive Vortex Generators for Flow Control on High-Speed Train

Abstract

Flow separation is one of the major causes of increase in aerodynamic drag. Vortex generators (VGs) are commonly used on cars and aircrafts to energize the boundary layer of the vehicle by mixing the high momentum flow from top to low momentum flow near the surface. This phenomena keeps the flow attached and delay flow separation, equivalently, the capability of flow to endure the adverse pressure gradient is enhanced. Vortex generators themselves add drag also in the form of viscous drag, but the overall effect of installing VGs is beneficial. Proper design of vortex generators plays a vital role in order to get maximum beneficial results. In present work, a very long high-speed train (204 m) is given herein to demonstrate flow control effect of vortex generators (VGs). Numerical studies are given via varying the configurations, size and orientations of VGs. The model selected for analysis is very similar to Chinese Railway High speed trains (CRH trains) having viscous drag as predominant drag and comparatively less contribution of pressure drag. Triangular, rectangular and trapezoidal shapes of VGs in co-rotating and counter rotating configurations are analyzed in present research. After the investigation of parameters of VGs on train model under analysis, it is found that the best shape and arrangement of VGs is triangular co-rotating VGs present at zero degree angle to each other. Triangular co-rotating VGs successfully reduced pressure drag of train model as much as 16.11% and increased viscous drag of train model by 0.055%. Change in total drag of the present train model is 1.03% drag reduction by installing 4 pairs of triangular co-rotating VGs. This reduction of total aerodynamic drag by 1.03% is very crucial, as it corresponds to millions of Kilowatt-hours (KWh) of electrical energy saving every year in high speed trains.