Comparison of industrial and scientific CFD approaches for predicting cross wind stability of the NGT2 model train geometry

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 modeling assumptions. Because of its relevance for actual design, a focus lies on steady RANS computations, but more expensive unsteady RANS (URANS) and delayed detached eddy simulations (DDES) have also 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 30o, 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.

[1]  A. Jameson.  Artificial diffusion, upwind biasing, limiters and their effect on accuracy and multigrid convergence in transonic and hypersonic flows , 1993 .

[2]  Ben Diedrichs,et al.  On computational fluid dynamics modelling of crosswind effects for high-speed rolling stock , 2003 .

[3]  R. C. Swanson,et al.  On Central-Difference and Upwind Schemes , 1992 .

[4]  Ralf Heinrich,et al.  The DLR TAU-Code: Recent Applications in Research and Industry , 2006 .

[5]  Hrvoje Jasak,et al.  A tensorial approach to computational continuum mechanics using object-oriented techniques , 1998 .

[6]  J. Munday,et al.  Measurements of the cross wind forces on trains , 2004 .

[7]  Sophie Papst,et al.  Computational Methods For Fluid Dynamics , 2016 .

[8]  Sinisa Krajnovic.  Computer Simulation of a Train Exiting a Tunnel through a Varying Crosswind , 2008 .

[9]  Uwe Fey,et al.  Transition Detection by Temperature-Sensitive Paint , 2007 .

[10]  Sinisa Krajnovic,et al.  LES study of the influence of the nose shape and yaw angles on flow structures around trains , 2010 .

[11]  Uwe Fey,et al.  Numerical and Experimental Studies of Train Geometries Subject to Cross Winds , 2014 .

[12]  Eli Turkel,et al.  Comparison of Several Dissipation Algorithms for Central Difference Schemes , 1997 .

[13]  F. Durst,et al.  Flow structure around trains under side wind conditions : a numerical study , 2000 .

[14]  Sinisa Krajnovic,et al.  LES Study of the Influence of a Train-Nose Shape on the Flow Structures Under Cross-Wind Conditions , 2008 .

[15]  Sinisa Krajnovic,et al.  Large eddy simulation of the flow around a simplified train moving through a crosswind flow , 2012 .

[16]  Christian Klein,et al.  Investigation of Reynolds Number Effects in High-Speed TrainWind Tunnel Testing using Temperature-Sensitive Paint , 2013 .

[17]  Hrvoje Jasak,et al.  Error analysis and estimation for the finite volume method with applications to fluid flows , 1996 .

[18]  Christopher Baker.  Some complex applications of the “wind loading chain” , 2003 .

[19]  Sinisa Krajnovic.  On Unsteady Simulations in Train Aerodynamics , 2014 .

[20]  J. M. Copley,et al.  The three-dimensional flow around railway trains , 1987 .

[21]  T. W. Chiu,et al.  An experimental study of the flow over a train in a crosswind at large yaw angles up to 90 , 1992 .

[22]  Branislav Basara,et al.  Simulation of the flow around high speed trains meeting each other and at the exit of a tunnel , 2009 .