WIND-TUNNEL TESTS TO OBTAIN TRAIN AERODYNAMIC DRAG COEFFICIENTS - REYNOLDS-NUMBER AND GROUND SIMULATION EFFECTS

An assessment is made of the effect of different types of ground simulation on wind tunnel measurements of the aerodynamic drag of trains, together with an assessment of Reynolds number effects which must be considered when extrapolating from model scale to full scale values. Drag coefficients are considered for two train types, the French TGV001 and the British HST. It is shown that the errors involved in extrapolating values of drag coefficient from model scale to full scale are significantly greater than possible errors caused by inadequate ground simulation. These extrapolation errors seem to be due to significant three-dimensionality in the train boundary layers, and it is suggested that these effects warrant further research.