Base Pressure Fluctuations

Abstract

The intense vibration accompanying the extension of dive brakes and other high drag devices on aircraft and missiles has been observed for many years. Recently, considerable vibration has been experienced at the fundamental longitudinal mode and at other internal resonance frequencies of a vehicle which had a blunt base during the maximum dynamic pressure phase of flight. In both cases the vibration is believed to result from the turbulent fluctuations in the wake of the base or drag device. The base pressure fluctuations have been measured at two base positions on a small body of revolution at eleven points in the velocity range of 68 to 352 ft/sec. The results show that (a) the ratio of (〈p2〉)12/q varies between 0.007 at the center of the base to 0.015 at 65% radius; (b) the spectrum of the pressure fluctuations is a function of the body Strouhal number; (c) the variation of observed vibration response with flight parameters can be predicted from the base pressure fluctuation data. (Work performed jointly with Norair, Division of Northrup Corporation in conjunction with U. S. Air Force contract.)