This thesis is a report of an experimental investigation of boundary layer transition from laminar to turbulent flow in hypersonic, high enthalpy flows over a flat plate. The experiments were conducted in a free piston shock tunnel at freestream Mach numbers ranging from 5 to 6.5 and unit Reynolds numbers from 1.25x106 m -1 to 2.08x107 m -1 The flow stagnation enthalpy varied from 2.35 MJ/kg to 19.2 MJ/kg. The onset of transition was detected by means of surface heat transfer measurements. Experimental results indicated that transition onset Reynolds number can be correlated with freestream unit Reynolds number. A semi-empirical correlation has been formulated. The effects of Mach number and wall cooling on transition Reynolds number are incorporated into this correlation. The prediction of heat transfer rate in transition region, as well as the dimension of transition region are discussed.
Freestream disturbances in the shock tunnel flow were found to be centered around relatively low characteristic frequencies, proportional to the square root of freestream temperature. Linear stability theory indicated that the freestream disturbances spectrum was not in a range likely to influence transition.
Pitot heat transfer measurements were taken across the boundary layer, and the inferred velocity profiles agreed well with predictions in the turbulent regions. This was taken as supportive evidence of the onset of transition as indicated by surface temperature measurements.