Flow control with rotating cylinders

Abstract

We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47, 000 with a three-dimensional and turbulent wake, Particle Image Velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45%. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapse with respect to a new scaling, which indicates that the control mechanism is viscous.

Flow control over a circular cylinder using virtual moving surface boundary layer control

“…The previous studies of MSBLC using small control cylinders suggested that the drag reduction is sensitive to the diameter of the control cylinder (Schulmeister et al 2017). Therefore, the vortex radius of the induced vortex C deserves consideration, due to the induced vortex C acting as the control cylinder of MSBLC.…”

“…As a typical active flow control technique, the moving surface boundary layer control (MSBLC) can be traced back to the last century (Ericsson 1994) and has been demonstrated to be an effective method for reducing drag of a bluff body (Kumar et al 2011;Korkischko and Meneghini 2012;Schulmeister et al 2017) and increasing lift of an airfoil (Modi et al 1998;Ericsson 1994) by means of a moving element (as shown in Fig. 1), such as rotating control cylinders, and drawn much attention because of its significant control effect.…”

“…1), such as rotating control cylinders, and drawn much attention because of its significant control effect. The highest drag reduction by MSBLC was 45% when the drag of control cylinders was not considered (Schulmeister et al 2017). The controlling drag reduction mechanism by MSBLC was investigated and explained by Schulmeister et al 2017.…”

“…The highest drag reduction by MSBLC was 45% when the drag of control cylinders was not considered (Schulmeister et al 2017). The controlling drag reduction mechanism by MSBLC was investigated and explained by Schulmeister et al 2017. They showed that the controlled steady flow field has a recirculating region that is bounded by a dividing streamline that separates from and then reattaches to the main cylinder, as shown in Fig.…”

“…1. Thus, there was a pressure recovery over the main circular cylinder, from separation to reattachment (Schulmeister et al 2017). The control cylinder imparted momentum to the near-wall fluid along the dividing streamline by promoting mixing, and injected momentum into the wake.…”