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International Journal of Railway Technology
IJRT, Volume 4, Issue 1, 2015
Comparison of Industrial and Scientific CFD Approaches for predicting Cross Wind Stability of the NGT2 Model Train Geometry
M.M. Fragner1, K.A. Weinman1, R. Deiterding1, U. Fey1 and C. Wagner1,2
1German Aerospace Center, Institute of Aerodynamics and Flow Technology, Goettingen, Germany
M.M. Fragner, K.A. Weinman, R. Deiterding, U. Fey, C. Wagner, "Comparison of Industrial and Scientific CFD Approaches for predicting Cross Wind Stability of the NGT2 Model Train Geometry", International Journal of Railway Technology, 4(1), 1-28, 2015. doi:10.4203/ijrt.4.1.1
Keywords: trains aerodynamics, cross-wind stability, drag prediction, computational fluid dynamics, experiments, vortex shedding, RANS, URANS, DDES.
Safety assessments of cross-wind influence on high-speed train operation require 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. Utilizing the DLR's Next Generation Train 2 model geometry, we have performed a case study comparing simulations with varying turbulence modelling assumptions. Because of its relevance for actual design, the focus lies on steady RANS computations, but more expensive unsteady RANS (URANS) and delayed detached eddy simulations (DDES) also have been carried out for comparison. Validation data for the exact same model configuration and moderate Reynolds numbers 250,000 and 450,000 is provided by side wind tunnel experiments. Particular emphasis is laid on simulating a yaw angle of 30°, for which a major vortex system on the leeward side of the train leads to sizeable uncertainties in predicted integral coefficients. At small to intermediate wind angles the flow remains attached and absolute errors in integral quantities decline with decreasing yaw angles. However, a consistent relative difference to the experimental results greater than 10% raises doubts about the general reliability of CFD methods, that are not capable of capturing laminar-turbulent transition, which is observed for scaled models in industry type wind tunnel experiments.
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