Velocity profiles and pressure fluctuations in the boundary layer on the roof of a railway coach

A rake of Pitot tubes was used to measure velocity profiles in the tubulent boundary layer on the roof of an Intercity passenger coach travelling at speeds between 120 and 250 km/h. Results show that the relationship between boundary layer thickness and displacement thickness is similar to that found in the turbulent boundary layer on a flat plate. Problems associated with making measurements of fluctuating pressures within the boundary layer are dicussed, and measurements made by Betzhold and Gahlau within the boundary layer on the roof of an Intercity coach are analyzed. It is found that fluctuating pressures within the fully turbulent region of the boundary layer are identical to those that would be obtained on the surface of a flat plate under the same conditions.