Suppression of the unsteady vortex wakes of a circular cylinder pair by a doublet‐like counter‐rotation

Abstract

SUMMARYThe present investigation examines the suppression of unsteady, two-dimensional wake instabilities of a pair of identical circular cylinders, placed side-by-side normal to freestream at a low Reynolds number of 150. It is found that when the cylinders are counter-rotated, unsteady vortex wakes can be completely suppressed. At fast enough rotational speeds, a virtual elliptic body is produced by a closed streamline, strongly resembling a doublet potential flow.

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

“…These streaklines, shown in figure 9, clearly show the presence of the stagnation point in the wake of the cylinder pair, indicating the presence of the virtual elliptical body above a certain rotational speed. This also confirms the predictions of Chan & Jameson (2010) made using a lower order numerical simulation. Vortex suppression and drag reduction in the wake of counter-rotating cylinders 353 The lift and drag coefficients are defined by…”

“…The unsteady regime at g * = 0.7 produced a single vortex street, while a larger gap spacing yielded either in-phase or anti-phase synchronous vortex shedding. Chan & Jameson (2010) extended this work by showing that the unsteady vortex wake could be suppressed in the reverse doublet-like configuration as well. For Re = 150 and g * = 1, they show that Ω crit = 1.5 for the doublet-like configuration and 3.5 for the reverse doublet-like configuration.…”

“…It is in this speed range that the virtual elliptic body forms and grows larger with respect to the increasing speed. Also plotted on figures 10 and 11 are the results obtained by Chan & Jameson (2010) each cylinder is zero, at Ω ≈ 4.1, versus 4.3 from the previous study. This cross-over speed is where the lift force on each cylinder transitions from repelling to attracting.…”

“…When the two cylinders are put into counter-rotation, several recent numerical studies have shown that these wake instabilities can be attenuated and even entirely suppressed (Yoon et al 2007;Chan & Jameson 2010). Counter-rotation can be achieved in two different rotational configurations: the doublet-like and reverse doublet-like configuration, as shown in figure 2.…”

“…We refine the previous numerically obtained results using a higher order simulation method, and confirm the computations using physical experiments. In the work by Chan & Jameson (2010), the simulations were performed with a commercial computational fluid dynamics (CFD) code for incompressible flow simulations, CFD-ACE+, from the ESI Corporation. In the current work, we use a high-order spectral difference (SD) method developed recently for compressible flow simulations.…”