Dense gas boundary layer experiments - visualization, pressure measurements, concentration evaluation
This report describes methods that were applied to investigate turbulent boundary layers generated by inviscid, baroclinic effects. A Cranz-Schardin camera was used to visualize the interaction of a planar shock wave with a Freon R 12 layer. The shock propagates more slowly in the Freon layer than in air because of its smaller sound speed. This causes the shock front to be curved and to be reflected between the wall and the layer interface. As a consequence of the reflection process, a series of compression and expansion waves radiate from the layer. These waves strongly perturb the interface shear layer, which rapidly transitions to a turbulent flow. Pressure measurements showed that the fluctuations in the Freon layer reach a peak pressure 4 times higher than in the turbulent boundary flow. Concentration measurements were performed with a differential interferometry technique. The evaluation of the concentration preshock profile is described in detail.