74th Annual Meeting of the APS Division of Fluid Dynamics
Volume 66, Number 17
Sunday–Tuesday, November 21–23, 2021;
Phoenix Convention Center, Phoenix, Arizona
Session P24: Vortex Dynamics and Vortex Flows: Propulsion and Wakes
4:05 PM–6:41 PM,
Monday, November 22, 2021
Room: North 224 B
Chair: Mark Stremler, Virginia Tech
Abstract: P24.00009 : Spanwise Wake Structure of a Yaw-Oscillating Cylinder at Subcritical Flow
5:49 PM–6:02 PM
Abstract
Presenter:
Ronald E Hanson
(York Univ)
Authors:
Vahid Nasr Esfahani
(York Univ)
Ronald E Hanson
(York Univ)
Alis Ekmekci
(University of Toronto)
An experimental study is carried out on the spanwise variation of the near wake of a yaw-oscillating circular cylinder. The yaw angle during oscillations varies from θ = 0o (exposing cylinder directly to crossflow) to θ = 30o at two Reynolds numbers of 5×103 and 1.5×104. Two different length-to-diameter ratios of 20 and 13 are tested. Planar Particle Image Velocimetry measurements were performed in vertical symmetry planes and horizontal planes orthogonal to the axis of the non-yawed cylinder to investigate the flow structure in the near wake region of the yaw-oscillating cylinder. The range of oscillation frequencies, which when expressed non-dimensionally in terms of reduced frequencies (K) vary between K = 0.5 to 4. For a cylinder undergoing yaw oscillation, the near wake is highly three-dimensional and the spanwise variation with the phase of oscillation is significantly dependent on the yaw angle and the direction of motion of the cylinder. Increasing yaw angle in the first half of the oscillation cycle leads to a shorter wake closure length and occasional suppression of the mean recirculation region (depending on the reduced frequency) near the upper-middle section of the cylinder whereas the wake closure length is generally elongated on the lower-middle section. This trend is reversed when the cylinder returns to the cross-flow position. Moreover, in the return cycle, at yaw angles in the range of θ = 15o to 30o, the strong axial flow generated from the upstream end of the cylinder develops on the lower half of the span of the cylinder intensifies the suppression of the mean recirculation region. The axial flow extends more rapidly on the span of the cylinder with the higher length-to-diameter ratio at moderate reduced frequencies. However, at high reduced frequencies, the role of axial flow is shown to be diminished and the suppression of the mean recirculation region along a large section of the span occurs under the impact of the cylinder rapid motion.