Unsteady pressure loads generated by swept-shock-wave/boundary-layer interactions

An experimental research program providing basic knowledge and establishing a database on the fluctuating pressure loads produced on aerodynamic surfaces beneath three-dimensional shock-wave/boundary-layer interactions is described. A turbulent boundary layer on a flat plate is subjected to interactions with swept planar shock waves generated by sharp fins at angle of attack. Fin angles from 10 to 20 deg at freestream Mach numbers of 3 and 4 produce a variety of interaction strengths from weak to very strong. Miniature pressure transducers flush mounted in the flat plate are used to measure interaction-induced wall pressure fluctuations. The distributions of properties of the pressure fluctuations, such as their rms levels and power spectra, are determined. These are combined with and explained in light of the previously known features of the interaction flowfield. In particular, physical mechanisms responsible for the generation of high levels of surface pressure fluctuations are proposed based on the present results. Attention has been focused for the first time on the aft regions of these interactions, revealing fluctuating pressure levels as high as 155 dB. These fluctuations are dominated by low-frequency components and are caused by a previously unrecognized random motion of the primary attachment line. The maximum rms levels in the interactions show an increasing trend with increasing interaction strength. On the other hand, the maximum rms levels in the forward portion of the interactions decrease linearly with increasing interaction sweepback. Nomenclature A = attachment / = frequency G(/) = power spectral density ^shock = length of region of intermittent separation shock translation M = Mach number P = pressure