Fluctuation measurements in the near wake of a slender wedge at Mach 4.0 with and without base injection

An experimental investigation of the turbulent and transitional near wake of an adiabatic, slender wedge with and without base injection was performed in the JPL Supersonic Wind Tunnel at Mach 4. Two different quantities were measured with a constant current hot wire anemometer, the mean square fluctuation intensity (f – 0.1 to 80 KC), and the frequency spectrum of the fluctuations (f = 5 to 200 KC, bandwidth 0.2 KC). The various flow regions of the near wake were identified and the growth and decay of flow fluctuations were determined. Helium and nitrogen were used as injectants and similar effects were obtained when He = N2. The flow fluctuations of the turbulent boundary layer remnant rapidly decayed during the expansion, and the inner shear layers and the reverse flow region which they bound were laminar. Base injection was found to significantly alter the near wake instability mechanism, which resulted in the delay of wake transition