Flow topology and unsteady features of the wake of a generic high-speed train

• The wake topology of a high-speed train has been investigated experimentally.
• A streamwise counter-rotating vortex pair and an arch vortex have been identified.
• Signs of vortex shedding off the tail sides and roof have been observed.
• Periodicity has been identified at a Strouhal number of 0.2.
• The vortex shedding results in periodic oscillations of the streamwise vortices.

The unsteady wake of a high-speed train is investigated experimentally. From a practical point of view, the wake region is of considerable importance as it is where slipstream velocities—velocities induced by the vehicles movement through air—are largest. In turn, this can create a considerable risk for passengers and track-side workers as the train passes. The flow is quantified in a 1:10 scale wind-tunnel experiment using high-frequency 4-hole dynamic pressure cobra probes, surface-pressure measurements and flow visualisation. The dominant feature of the time-average wake topology consists of a clearly identifiable counter-rotating streamwise vortex pair. Although the wake structure and evolution should perhaps be considered as a whole, the near wake exhibits periodic unsteadiness, at a Strouhal number of 0.2, that could be attributed to periodic shedding from the sides and to a lesser extent the top surface. This periodicity feeds into the trailing vortices, consistent with lateral and vertical displacement of the cores as they advect downstream and thus affecting maximum slipstream velocities.

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