Open-loop and Closed-loop control of a Flow over a Cluster of Three Cylinders with Variable Spin Rate in Equilateral Triangular Arrangement
Date
2020-01-30
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Abstract
The control of the flow over a cluster of three rotating cylinders arranged in a triangular configuration (pinball-configuration) is simulated using 2D URANS. The free stream flow impinges onto the front cylinder at Reynolds number of 2054 based on the diameter. Open-loop and closed-loop controls change the flow behavior because the rotating surfaces of the cylinders directly modify the vorticity flux into the wake. For the open-loop control, the leeward cylinders are counter-rotating at a constant rate. In the open-loop control, the strength of the shear layers from the leeward cylinders and the central gap flow change and even reverse as the rotation rate varies. As a result, different and unique flow states were realized. The fluctuation of the flow reaches a minimum at certain rotation ratio (angular velocity of a cylinder non-dimensionalized by free-stream flow velocity). In the closed-loop control, the fluctuating lift of each cylinder is used as a feedback signal to control an oscillatory rotation rate about the mean that is set to match an open-loop configuration. The physical model describing the rotation-induced-lift by oscillatory rotation is developed and reveals a phase lag between 0 to pi from the steady-state-lift. Based on this mechanism, a closed-loop controller is designed such that the rotation-induced-lift partially cancels the lift from the natural vortex shedding. This results in lift attenuation. The closed-loop control is tested on the single cylinder case, revealing that the shear layers are elongated and the strength of the vorticity flux across each shear layer is reduced. The closed-loop control is then applied to the pinball-configuration. The same elongation of the shear layers and the reduction in the strength of vorticity flux are observed. Additionally, the closed-loop control changes the central gap flow, which slightly shifts the flow characteristics accordingly.
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Keywords
rotating cylinder, vortex interaction, flow control, closed loop, open loop, vortex shedding, vortex merger, bluff bodies, gap flow, Magnus, Coanda, potential flow, induced vortex, induced lift, phase delay, phase lag, pinball, cluster of cylinders, shear layer, shear layer interference, shear layer interaction, blowing, suction, oscillatory rotation, vorticity flux, CFD, URANS, adaptive mesh, lift attenuation
Citation
Zhong, X. P. (2020). Open-loop and Closed-loop control of a Flow over a Cluster of Three Cylinders with Variable Spin Rate in Equilateral Triangular Arrangement (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.