Wake modes of rotationally oscillating cylinders at Re=150

Vortex shedding and heat transfer in rotationally oscillating cylinders

“…They explained the 'non-lock-on' regime as being caused due to far-wake instabilities and identified boundaries between lock-on and non-lock-on regions. In Sellappan & Pottebaum (2014) and in the present study, it was observed that this kind of mixed frequency content is actually indicative of a transition between lock-on and a total non-lock-on regime in which the forcing frequency is almost completely absent from the spectra. Thiria & Wesfreid (2007) 554 P. Sellappan and T. Pottebaum …”

“…This is seen in both cases, heated and unheated cylinder. While these kind of sharp transitions have been observed at lower Re for an unheated cylinder (Sellappan & Pottebaum 2014) and it is not surprising to observe it for an unheated cylinder at Re = 750, in the present study, it was also observed for a heated cylinder. Previous studies that looked at transversely oscillating cylinders found that in the case of a heated cylinder the transition regions are mostly smooth, with some test cases on the boundary even exhibiting a periodic mode switching (Pottebaum 2003).…”

“…Experimental studies have been performed by Tokumaru & Dimotakis (1991), Fujisawa, Kawaji & Ikemoto (2001), Fujisawa, Tanahashi & Srinivas (2005), Lee & Lee (2006), Saad, Lee & Lee (2007), Lee & Lee (2008), Nazarinia et al (2012) and, most recently, Kumar et al (2013) 552 P. Sellappan and T. Pottebaum and Sellappan & Pottebaum (2014). Tokumaru & Dimotakis (1991) conducted an experimental study at Re = 15 000, performing flow visualization and wake profile measurements on circular cylinders undergoing forced rotary oscillations in a steady uniform flow and found that the drag forces on the cylinder were reduced at high oscillation frequencies while undergoing rotary forcing.…”

“…They also found the wake to be locked-on to the forcing when F R = 1.0, but observed only a transition regime when F R = 0.8, 1.6 and a non-lock-on regime when F R = 0.4. Most recently, Sellappan & Pottebaum (2014) showed experimentally that locked-on wake modes occur over a large range of forcing conditions for rotationally oscillating cylinders at Re = 150, including wake modes synchronized over multiple cylinder oscillation cycles. Wake mode boundaries identified by some of these authors are shown in figure 3.…”

“…This reduction in particle losses between frames reduces the measurement uncertainty. This DPIV system has been used by the authors in previous studies such as Sellappan (2013) and Sellappan & Pottebaum (2014) and the velocity measurements made using this set-up have relative uncertainties of 1.5-3 %. For all test cases presented here, 3500 images (1750 image pairs) with image resolution of 1024 × 768 pixels were acquired at 27 f.p.s.…”