DECAY OF THE TURBULENT WAKE FROM THE SUPERSONIC MICRO RAMP

The wake resulting from two micro ramps operating in a supersonic boundary layer at Ma = 2:0 is investigated by means of PIV. Two micro ramps are investigated with height of 60% and 80% of the undisturbed boundary layer with thickness of 5.2 mm. The measurement domain encompasses the range from 10 to 32 ramp heights downstream of the device. The decay properties are evaluated in terms of time-averaged and root-mean-square (RMS) statistics. In the time-averaged flow field, the recovery of the imparted momentum deficit and the decay of upwash motion are revealed. The RMS fluctuations of the velocity components exhibit strong anisotropy at upstream locations but develop into a more isotropic regime downstream. The Kelvin-Helmholtz (K-H) instability at the upper shear layer further develops with the onset of vortex pairing. The wavelength evolution is estimated using statistic-based spatial auto-correlation. A marked transition with the wavelength nearly doubled is observed across the pairing regime.