A novel passive flow control method employing vortex generators to suppress wake flow characteristics of a high-speed train: Mechanism and application

Abstract

This paper proposes a passive control method to reduce peak values of slipstream and turbulent kinetic energy in a high-speed train wake by attaching vortex generators (VGs) onto the upper surface of the tail car. The impact of the VGs is assessed through the improved delayed detached eddy simulations (IDDES) after validating predictions against previous experimental measurements and other numerical predictions for the base case. The simulations indicate that strategically installed VGs can reduce the average slipstream velocity (U_slipstream) and the upper limit of slipstream velocity (U_{slipstream, max}) by ∼17% and ∼15%, respectively, as well as moving the peaks downstream by approximately train height, thus reducing the danger posed by slipstream to waiting passengers and trackside workers. Analysis shows that the wake turbulent kinetic energy diminishes as the vortex generators decelerate the downwash flow and reduce shear production in the wake. It is also found that the presence of VGs significantly impacts the flow on the upper surface near the tail by modifying the unsteady trailing longitudinal vortices through the formation of additional counter-rotating longitudinal vortices from the VGs. These latter vortices prevent the merging of vortical airflow around the trailing nose tip, which is otherwise induced by the longitudinal vortex of the train. They also reduce vortex intensity through cross-annihilation and cross diffusion as the wake advects downstream, limiting outwards advection through interaction with the image pair, and contributing to a decrease in the peak slipstream value. The method proposed offers a simple approach to wake control leading to significant slipstream benefits.

Keywords

high-speed train / vortex generators / slipstream / wakes / passive control

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