Fluctuating Pressure Environment of a Drag Reduction Spike

TLDR: In this article, the authors made measurements of the fluctuating pressure environment in a region of spike-induced flow separation at transonic speeds, which is related to the nonaxisymmetric, vortical nature of the separated flow at a>0.

Abstract: Wind-tunnel measurements have been made of the fluctuating pressure environment in a region of spikeinduced flow separation. Extremely large pressure fluctuations (30% of freest ream dynamic, pressure) were measured on the sides of the spike base at transonic speeds which are related to the nonaxisymmetric, vortical nature of the separated flow at a>0. Even higher (42% of freestream dynamic pressure) pressure fluctuations were observed on the windward side of the nose cap at supersonic speeds and a>7 deg. This is the result of an intermittent shock-shock interaction. The method of Coe et al. of normalizing the spectral data with the local separated flow height was moderately successful in collapsing the data into a manageable number of characteristic spectra. However, the spectra for the spike-induced separation at supersonic speeds agreed better with the results of Speaker and Ailman for two-dimensional step-induced separation than they did with the threedimensional ramp-induced separation of Coe et al. Spectral peaks were observed which corresponded to Roberts' critical subsonic wake flapping frequency.