Unsteady wall-pressure loading in a Mach 3 compression ramp flow at $Re_{\theta}=2400$.*

We perform experiments to investigate the unsteady wall-pressure behavior in a Mach 2.9 shock-wave turbulent boundary layer interaction. The flow configuration is a nominally two-dimensional $24^{\circ}$ compression ramp, and the Reynolds number based on momentum thickness is 2400. In contrast to measurements at higher Reynolds numbers (of order $10^4$--$10^5$), the results show a smaller peak in the RMS of the wall-pressure fluctuations, and the wall-pressure signal exhibits a much richer intermittency in the shock-foot region. Spectra show that the signal energy is more evenly distributed over the range of shock oscillation frequencies, resulting in a smaller peak energy than that found at higher Reynolds numbers. The shock motion has a broadband frequency distribution with a peak slightly below 1 kHz, similar to the higher Reynolds number data. We find good agreement with the direct numerical simulation of Wu~\&~Mart\'{\i}n\footnote{Wu, M. \& Mart\'{\i}n, M. P. Direct numerical simulation of supersonic turbulent boundary layer over a compression ramp. \textit{AIAA Journal} \textbf{45}(4), 2007, 879--889.} at matching conditions.