Vortex suppression and drag reduction in the wake of counter-rotating cylinders

Abstract

The flow over a pair of counter-rotating cylinders is investigated numerically and experimentally. It is demonstrated that it is possible to suppress unsteady vortex shedding for gap sizes from one to five cylinder diameters, at Reynolds numbers from 100 to 200, expanding on the more limited work by Chan & Jameson (Intl J. Numer. Meth. Fluids, vol. 63, 2010, p. 22). The degree of unsteady wake suppression is proportional to the speed and the direction of rotation, and there is a critical rotation rate where a complete suppression of flow unsteadiness can be achieved. In the doublet-like configuration at higher rotational speeds, a virtual elliptic body that resembles a potential doublet is formed, and the drag is reduced to zero. The shape of the elliptic body primarily depends on the gap between the two cylinders and the speed of rotation. Prior to the formation of the elliptic body, a second instability region is observed, similar to that seen in studies of single rotating cylinders. It is also shown that the unsteady wake suppression can be achieved by rotating each cylinder in the opposite direction, that is, in a reverse doublet-like configuration. This tends to minimize the wake interaction of the cylinder pair and the second instability does not make an appearance over the range of speeds investigated here.

Self-propulsion of a counter-rotating cylinder pair in a viscous fluid

“…This is similar to the flow obtained past a stationary rotating cylinder pair with suppressed wake. 12 In contrast, at the higher Reynolds number, there is a closed region of fluid around each cylinder. The incoming flow is distributed around and in between the cylinders, reminiscent of a jet-like flow where the fluid is ejected through the opening between the cylinders.…”

“…9 Since then, several authors have presented extensive analytical studies for the behaviour of the flow at low Reynolds numbers. 10,11 Numerical results for the flow past a fixed counter-rotating cylinder pair at non-zero Reynolds numbers were presented by Chan et al 12 They found that for certain combinations of inflow and rotational velocities, the vortical wake was suppressed resulting in zero or negative drag values. In the context of self-propulsion, steady-state solutions were found numerically for two counter-rotating cylinders 13,14 and an axisymmetric torus.…”

Performance enhancement of downstream vertical-axis wind turbines

“…Higher-order effects such as the manipulation of vortex shedding, which has been found to be significant for counter-rotating cylinders 26 and in stationary cylinders in close proximity, 27 should be further investigated in the context of VAWT wind farm design.…”

Flow Patterns and Heat Transfer Around Six in-Line Circular Cylinders at Low Reynolds Number

“…The advection terms in the equations (2) and (4) of Chan et al 2011, Park et al 1998, Sharman et al 2005, Ding et al 2007(see table II). …”

“…The simple two cylinders configuration has been discussed extensively and it represents a starting point to study the flow around multiple bluff bodies (Ben Meftah and Mossa 2013, Chan et al 2011, Jester and Kallinderis 2003, Prasanth and Mittal 2009, S. Mittal and Kumar 2001, Sharman et al 2005, Sumner et al 2000. According to the literature, a well-known drag inversion separation has been identified.…”