Wall Shear Stress Measurements on a Double-Decker Train

The aerodynamic drag is the principal factor of the driving resistance of modern railway vehicles. To accurately predict the energy consumption, it is essential to estimate the drag that is fundamental for the development of new vehicles. One way to quantify the aerodynamic drag of a full-scale railway vehicle is to measure the wall shear stress since friction drag dominates. The goal of this study was to improve the prediction of the aerodynamic drag of railway vehicles by measuring the wall shear stress. Experiments were performed on a double-decker multiple-unit train KISS from Stadler to measure the wall shear stress under real operating conditions. Oil-film interferometry was used as a non-intrusive measurement technique with the setup installed inside the train to avoid flow disturbances induced by measuring probes. The obtained results are in good agreement with experimental full-scale data from the literature. The comparison to theoretical predictions based on pipe and flat plate experiments reveal clear deviations.