Using appropriate boundary layer tripping on high-speed train models used in wind tunnel experiments to minimize Reynolds number effects

Kurzfassung

Wind tunnel testing of high-speed trains is mainly concerned with the experimental determination of force- and moment coefficients to be used for stability calculations with respect to wind-induced de-railing risks. For the gathered data, a Reynolds number dependency of the results is observed. The European and national standards treat the problem of Reynolds number independency for wind tunnel results differently, to make the obtained coefficients reliable. However, the reason for Reynolds number sensitivity has not been really addressed so far. Based on experiment¬tal investigations of the wall-bounded flow structures, it is shown in this paper that (laminar) flow separation alongside the windward roof edge represents a source for Reynolds number dependency, seen especially in the lift-force coefficient. Based on the topology of these flow structures, selective boundary layer tripping is applied to minimize Reynolds number effects with only small influence on the global flow field