The effect of numerical divergence schemes on the flow around trains

What is it about?

The influence of divergence schemes in typical turbulence modelling on the aerodynamic behaviours was investigated in this study. Four common divergence schemes have been used to predict the aerodynamic behaviours of a typical train in crosswinds, including the first order upwind differencing (UD), second order limited-linear differencing (LL), linear-upwind differencing (LU) and Linear-upwind stabilized transport (LUST) schemes. Shear Stress Transport (SST) k– turbulence model and Improved Delayed Detached Eddy Simulation (IDDES) were applied to simulate the aerodynamic characteristics of the train. Both SST and IDDES with the above three kinds of the second order divergence schemes are capable of predict accurately the pressure coefficient.

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Why is it important?

Results obtained using SST with the second order discretisation schemes gave similar streamline trends around the train nose and as anticipated, results from the first order UD scheme showed poor comparison. Results obtained using IDDES showed sensitivity to the divergence schemes, and different schemes performing differently in predicting the surface pressure on different parts of the car body. Considerable differences in the force coefficient using IDDES were observed between the LUST and the other schemes. The second order upwind LU scheme is not recommended for IDDES of the flow around trains.