Tomographic Particle Image Velocimetry Measurements in a Bluff-Body Wake Flow

Abstract

I N the wake of bluff bodies, flow separation occurs along with phenomena like recirculation, increased turbulence levels, periodic shedding processes, and low-pressure regions. For flow bodies, which cannot avoid such geometries, base drag and buffeting effects can vitally reduce performance and efficiency. This holds true for axisymmetric, cylindrical bodies placed parallel to freestream direction, like the generic rocket configuration considered in the current work. Similar geometries were studied extensively for subsonic freestream conditions, with early studies concentrating on static or time-averaged quantities [1,2]. Following the evolution of both experimental and numerical methods, the unsteadiness of the wake turned into focus. Many studies reported a macroscopic vortex shedding mode at a reduced frequency of StD 0:2 [3–5], that was also detected in hot-wire and dynamic base pressure measurements regarding the present case [6]. The instability of the shear layer is assumed to be a key factor in the shedding mechanism and the wake topology [4]. Correspondingly, Pastoor et al. [7] used zero-net-massflux actuation to actively manipulate the shear layer of a bluff body over wide Reynolds ranges. A possible overall drag reduction of 15% was reported. Perret [8] investigated the wake of a quasitwo-dimensional (2-D) cylinder by means of two-component (2C) particle image velocimetry (PIV) for ReD 1:25 10 [8]. Within the shear layer, a vortex population was detected using the swirling strength criterion. The corresponding structures were both small (<5% of the model diameter) and of high intensity compared to the macroscopic Karman vortices, and, thus, connected to the Kelvin– Helmholtz instabilitymechanism. It was also pointed out that for 2-D measurements, only the planar swirling motion can be taken into account and may be affected or biased by the out-of-plane velocity and inclined vortex axes [8]. Fewer results can be found regarding three-dimensional (3-D) test cases. Deck and Garnier [5] performed both detached and large eddy simulations (DES/LES) on the wake flow of a cylindrical, generic launch vehicle model. The bluff base geometry was prolonged by a Presented at the 41st AIAA Fluid Dynamics Conference and Exhibit, Honolulu, Hawaii, June 27–30, 2011; received 27 November 2011; revision received 10 April 2012; accepted for publication 11 April 2012. Copyright © 2012 by Institute of Aeronautics and Astronautics, RWTH Aachen University. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Copies of this paper may be made for personal or internal use, on condition that the copier pay the $10.00 per-copy fee to the Copyright ClearanceCenter, Inc., 222RosewoodDrive,Danvers,MA01923; include the code 0001-1452/12 and $10.00 in correspondence with the CCC. Research Engineer, Wuellnerstr 7. Member AIAA. Senior Research Engineer, Wuellnerstr 7. AIAA JOURNAL Vol. 50, No. 12, December 2012