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Keywords: trains aerodynamics, cross-wind stability, drag prediction, computational fluid dynamics, experiments, vortex shedding, RANS, URANS, DDES.

Abstract

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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Front Page Browse CCP CSETS CTR IJRT Other Authors Search Purchase Guide FAQ Contact us	International Journal of Railway Technology ISSN 2049-5358 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. Wagner^1,2 ¹German Aerospace Center, Institute of Aerodynamics and Flow Technology, Goettingen, Germany ²Technical University Ilmenau, Institute of Thermodynamics and Fluid Mechanics, Ilmenau, Germany doi:10.4203/ijrt.4.1.1 purchase the full-text of this paper Full Bibliographic Reference for this paper 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. Abstract 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. purchase the full-text of this paper (price £20) go to the next paper return to the table of contents return to IJRT purchase this issue (price £70 +P&P)
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