Wavenumber-Frequency Spectra on a Launch Vehicle Model Measured via Unsteady Pressure-Sensitive Paint

Time histories of pressure fluctuations on a generic, " hammerhead" launch vehicle model were measured using unsteady pressure-sensitive paint over a Mach number range of 0.6 = M = 1.2. The calibration process, using a set of unsteady pressure sensors, was found to overcome some of the inherent problems of the fast-response paint, such as rapid photodegradation, nonlinearity in pressure response, and significant temperature sensitivity. The large data set exposed various critical transonic flow physics such as a coupling of the shock motion on the payload fairing (PF) with the separated flow region downstream, and an upstream convection of pressure fluctuations on the PF at certain Mach numbers. Area-weighted integration of the pressure fluctuation data provided a measure of the unsteady forces on various parts of the model. The unsteady force coefficients on the PF and the upper stage were the highest when transonic shocks were present and found to reduce significantly when supersonic flow set in. Time histories on a dense, regularly spaced, spatial grid points allowed for the calculation of wavenumber-frequency (k -.) spectra via Fourier transform. The k -. spectra were dominated by the convected fluctuations; the acoustic domain was not discernible. These data, valuable for the buffet and vibroacoustics analysis of aerospace vehicles, are believed to be the first obtained for the transonic flight regime.