Some Effects of Upstream Turbulence on the Unsteady Lift Forces Imposed on Prismatic Two Dimensional Bodies

Abstract

Measurements of fluctuating lift are reported from four fixed rectangular prisms and a fixed circular cylinder, for various intensities of turbulence in the oncoming stream. Variations of unsteady lift with intensity of small scale turbulence are similar to present (and previous) measured variations of mean drag or base pressure. Reasons are suggested for these trends. Observations are also reported of the maximum (resonant) RMS amplitude of two cylinders, one square and the other circular in cross section, free to move in the cross stream direction. Small scale free stream turbulence provided by the wake of a small upstream rod increased the resonant amplitude of motion in both cases, the greater increase (and subsequent decrease) occurring for the square section. Two possible explanations for these observations are advanced.