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Experimental stability studies were conducted in the transition region from laminar to turbulent flow in wakes of slender wedges and a flat plate at Mach number 6. As in low-speed flat plate wakes, transition from laminar to turbulent flow may be divided into a linear and a nonlinear instability region. In viscid linear stability theory predicts well the growth of fluctuations and amplitude distribution in the linear region. In the nonlinear region similarities with low-speed wakes exist. Characteristic persisting peaks in the power spectra are observed. Based on these peak frequencies a nearly universal Strouhal number offbo/u m = 0.3 was found for both incompressible and hypersonic wake flows. A theoretical approach to predict the development of mean flow and flow fluctuations in the nonlinear region as employed by Ko, Kubota, and Lees in slender body low-speed wakes appears equally applicable for hypersonic wakes. Nomenclature b = wake width 6 0 = wake width at neck based on velocity profile c = phase velocity (= CR -f ia) c g = group velocity e' -hot-wire fluctuation voltage Ae = hot-wire sensitivity coefficient / = frequency H -wedge base height i = hot-wire current L -flat plate length m = mass flow (= pu) M = Mach number R w -hot-wire resistance Re = Reynolds Number S = Strouhal number (= fb/u e ) To = total temperature a -wave number 5 = wedge angle p -density 6 = momentum thickness Supe r scrip ts ( )' = fluctuation quantity C^_Y -r ms of fluctuation quantity ( ) = mean flow quantity Subscripts wake edge quantity quantity at frequency / reference quantity freestream quantity ). = )/ = )r =

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