Leading-edge sweepback and shape effects on fin-induced fluctuating pressures

Abstract

Measurements of the fluctuating wall pressure have been made on centerline upstream of blunt fins in a Mach 5 turbulent boundary layer. Leading-edge sweep considerably reduces the mean and rms pressure loading at the fin root, the extent of the region of unsteady separation shock motion (i.e., the intermittent region), and the separation length. The frequency of shock-induced pressure fluctuations in the intermittent region increases with leading-edge sweepback, while frequency spectra in the separated region are virtually unchanged. A strake at the root of an unswept fin has virtually no effect, whereas a swept blunted root fillet reduces the upstream influence and intermittent region lengths by 50%, and reduces the mean and rms pressure loading at the fin root by about 75% and 95%, respectively. Experiments using hemicylindrical, wedge-shaped, and flat leading edges show that separated-flow scales and root loading increase with increasing bluntness (i.e., wedge to hemicylinder to flat), while the intermittent-region length increases (in terms of fin thicknesses). The changes in flowfield unsteadiness are related to changes in separated-flow structure which alter the dynamics of the primary vortex and recirculation process.