Numerical simulation of side wind effects on a high-speed train. The DLR Institute of Aerodynamics and Flow Technology in Göttingen is equipped with special wind tunnels with the latest modern optical measurement equipment. For the first time, air flow and density field surveys for high-speed train models are being tracked in the Cryogenic Wind Tunnel in Cologne, and in the High-Pressure Wind Tunnel, in Göttingen (both are part of the German-Dutch Wind Tunnels programme), providing a realistic simulation of the Reynolds number, a physical quantity used to characterise the flow of air around a moving object.