An Experimental Investigation of the Formation and Flow Characteristics of an Impulsively Generated Vortex Street

Abstract

In this shock tube investigation, the passage of a plane normal shock wave and its associated drift flow over a two-dimensional circular cylinder impulsively generated a vortex street. The operating free stream Reynolds and Mach number range was 3.25 × 104 ≤ Rn ≤ 2.03 × 105 and 0.193 ≤ M∞ ≤ 0.483, respectively. The formation of the initial standing pair of vortices, their shedding, and the subsequent establishment of the vortex street were recorded interferometrically using a high speed framing camera. The movement of the initial vortex pair was observed to be significantly altered for Rn > 1.5 × 105, where a secondary vortex pair was generated and merged with the initial vortex pair well before shedding commenced. During the lifetime of the impulsively generated wake, the Strouhal number, S, approached an average value of 0.16 which is significantly lower than the usual steady-state value of about S ≃ 0.2. Values of spacing ratio were found to decrease with increasing vortex street lifetime for all downstream locations. Other pertinent vortex street characteristics were also reported.