Fluctuating wall pressures near separation in highly swept turbulent interactions

Abstract

Fluctuating wall pressures have been measured in Mach 5 interactions generated by sharp, unswept fins at angles of attack of 16 to 28 deg. The results show that rms pressure distributions, like the mean, can be collapsed in conical coordinates. The wall pressure signal near separation is intermittent and is qualitatively similar to that measured in unswept interactions and other swept flows. However, the dominant separation shock frequencies in the swept flows are up to an order of magnitude higher than those in unswept interactions under identical incoming flow conditions. In light of the present observations, it appears that an earlier remark, by Gilson and Dolling, that separation is characterized by a "shuddering compression system, in contrast to a translating separation shock" is erroneous due to a combination of weak shock strength and inadequate spatial resolution. Furthermore, although the maximum rms pressure near separation increases with increasing interaction strength, as in swept compression ramp flows, comparison of data from the two flow types indicates that the appropriate correlating parameter is the interaction sweepback angle.

Spectral Characteristics of Separation Shock Unsteadiness

“…This behavior has now been observed in wind tunnel experiments for a variety of experimental configurations at Mach 2-5, including diffusers, ramps, flares, sharp fins, and cylinders/blunt fins. 10,13,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] Similar results have also been obtained in experiments in quiet wind tunnel facilities 34 and in flight experiments. 35 The position of the separation shock foot has been inferred from the intermittency of the wall-pressure signal using the nested boxcar conversion technique.…”

“…Some evidence of separation shock motion was evident in wall pressure time-histories and spectra (their Figs. [25][26]. Even greater fidelity has become possible in the last five years, as the computational resources have become available to run calculations out to physical times that are one to two orders of magnitude larger than the characteristic separation bubble time scale.…”

Progress in shock wave/boundary layer interactions

“…Dolling and colleagues have examined numerous such configurations including swept corners, sharp fins, blunt fins and doublefins [95,96,28,97]. There has been relatively little effort in this area during the last decade however.…”

Experimental Investigation of Unsteadiness of Swept-Ramp Shock/Boundary Layer Interactions at Mach 2

“…The mean flow structure is typical of what is expected of a swept ramp interaction [6][3] [7][8] [9]. The separation line is non-linear (curved) at its most upstream location, before becoming straight (conical scaling) at approximately one third of the ramp diameter (101.6 mm).…”