Keywords: train aerodynamics, high-speed train, compact train, three-dimensional boundary layer, longitudinal vortices, RANS simulations, wind tunnel tests, oil-film visualizations.

The aerodynamic design of a compact lightweight high-speed train is discussed. It is an isolated automotive vehicle with a capacity for forty passengers. The fore end geometry is very streamlined and the upper curvature radii are exceptionally large to delay flow separations. The particular duck-shape of the fore region of the nose is responsible for large transverse pressure gradients. The research, described in this paper, explores how the nose geometry and the yaw angle influence the pressure distribution and the three dimensional boundary layer on the nose of the train, causing limiting streamlines on the wall to converge along specific locations. A main goal is to understand if these patterns can be related with the onset of separations at yaw.

A semi-analytic model for the skewed boundary layer was compared with RANS calculations. RANS simulations failed to reproduce the expected wall profile and seem to overestimate the diffusion in the boundary layer. On the other hand, the semi-analytic model seems to underestimate diffusion and should be refined with a better model for Reynolds stresses effects on the buffer layer.

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