Numerical and Experimental Studies of Train Geometries subject to Cross Winds

Kurzfassung

Safety assessments of cross-wind influence on high-speed train operation requires a detailed investigation of the aerodynamic forces acting on a vehicle. European norm 14067-6 permits the derivation of required integral force and moment coefficients by experiments as well as by numerical simulation. Utilising the DLR’s Next Generation Train 2 model geometry, we have performed a case study using incompressible steady RANS simulations from the OpenFOAM fluid dynamics solver software. Validation data for the exact same model configuration and moderate Reynolds numbers 250,000 and 450,000 is provided by side wind tunnel experiments. Highly resolved cross verification computations with the compressible DLR TAU code confirm that yaw angles > 30 degrees create major vortex systems on the leeward side of the train leading to sizeable uncertainties in predicted integral coefficients. At low to intermediate wind angles the flow remains attached and absolute errors in integral quantities decline with decreasing yaw angles. A consistent relative difference to the experimental results greater than 10%, however, raises doubts about the suitability of the RANS approach for accurately assessing such configurations in general and indicates that such comparably inexpensive simulations, presently performed by routine in industry, will typically not be sufficient to satisfy the accuracy requirements of EN 14067-6.