High Speed Flow Separation Ahead of Finite Span Steps

Book excerpt: Detailed surface heat transfer data, oil flow, and schlieren photographs are presented for high speed flow separation ahead of finite span, forward facing steps on flat plates. Step spans were varied from three to ten times as large as the step height, and the step heights are three to four times larger than the undisturbed turbulent boundary layer thickness. Reynolds numbers, based on plate length, were approximately 15 million for both Mach 4.75 and Mach 5.04 local undisturbed flows over the flat plate surface. For these test conditions, the maximum extent of separation ahead of the step is approximately 4.4 times as large as the step height independent of step span, and peak heating rates were measured that are more than six to eight times larger than the undisturbed flow heating rates. Peak heating on the plate surface occurs slightly upstream and approximately 1/2 step height inboard of the outboard sides of the steps; the increase in peak heat transfer coefficients over the undisturbed flow values decreases with increasing step span. In addition to presenting the detailed surface heat transfer data, a plausible theoretical analysis is presented for calculating the region of turbulent boundary layer separation ahead of these finite span steps.