Hypersonic boundary layers

The design, instrumentation, and calibration of the Oxford University Hypersonic Gun Tunnel is described. The calibration included the determination of the working section Mach Number, total temperature, total pressure, and unit Reynolds Number. The performance was compared with theoretical estimates. Measurements of boundary layer transition on the outside surface of a hollow cylinder model using shadowgraph and surface pitot techniques are described. Transition experiments on the model in various European wind tunnels are compared and a correlation based on nozzle wall boundary layer aerodynamic noise radiation is discussed. Heat transfer measurements on the surface of a 10° total angle sharp cone and a flat plate were made and compared with theoretical predictions. Transition location based on changes in the heat transfer rate was determined for the two models and compared with the hollow cylinder results. Effects of model wall curvature were shown to be present and were correlated by the ratio of boundary layer thickness to wall radius of curvature. A fine hot wire constant temperature anemometer probe was developed and used to measure fluctuation levels through the transitional boundary layer of a flat plate. Strong fluctuation intensities were found within the boundary layer upstream of the region where transition begins based on mean surface heat transfer measurements. These fluctuations appeared to be due to large turbulent eddies generated near the model leading edge and were initially located in the boundary layer at a y/δ location consistent with compressible stability theory.