Flow and heat transfer across two inline rotating cylinders: Effects of blockage, gap spacing, Reynolds number, and rotation direction

• Published in: International journal of heat and mass transfer 2021-08, Vol.174, p.121324, Article 121324
• Main Authors: Rastan, M.R., Sohankar, A., Alam, Md. Mahbub
• Format: Article
• Language: English
• Subjects: Aerodynamic coefficients; Circular cylinders; Computational fluid dynamics; Convective heat transfer; Domains; Drag coefficients; Drag reduction; Flow mapping; Flow patterns; Fluid flow; Heat transfer; Laminar flow; Numerical simulation; Reynolds number; Rotating bodies; Rotating cylinders; Steady flow; Strouhal number; Tandem arrangement; Three dimensional flow; Topology; Unsteady flow; Vortex shedding
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2021.121324

•Aerodynamics and heat transfer over two rotating cylinders are investigated.•Rotating cylinders require a blockage ratio ≈ 1%, when α < 2.•The fluid forces are highly sensitive to the cylinder rotation when |α| > 2.•A flow map in a three-dimensional domain of S*, α and Re is provided. The manipulation of the heat transfer and flow field using cylinder rotation is of a classical issue. It is of fundamental importance to study the dependence of wake and thermal topologies of two rotating cylinders in tandem arrangements. This study numerically investigates the time-resolved laminar flow, fluid forces, Strouhal number, and convective heat transfer over two isothermal co-rotating and counter-rotating circular cylinders in tandem arrangements for scaled cylinder center-to-center spacing S* = 2.5 - 6, non-dimensional rotational speed |α| ≤ 5, and Reynolds number Re = 100 - 200. How Re, S*, α and computational domain size influence the wake dynamics and thermal attributes is the focus of this study. The numerical procedure is validated against the available data in the literature for a single rotating cylinder. The influence of the blockage ratio on the single- and two-cylinder flow is determined first to decide the appropriate computational domain. It is found that rotating cylinders require a larger computational domain (blockage ratio ≈ 1%, when α> 2) than stationary cylinders (blockage ratio = 5%). The fluid forces are highly sensitive to the cylinder rotation when |α| > 2. Although both cylinders undergo the same magnitudes of time-mean drag coefficient |C¯d| or time-mean lift coefficient |C¯l| at a given |α|, the cylinder rotation shifting from co-rotation to counter-rotation reverses the direction of C¯d, i.e. repulsive for the co-rotation and attractive for the counter-rotation. On the other hand, an increase in S* from 2.5 to 6 with α = 5 results in a 43% drag reduction for either cylinder. The S*, however, has an insignificant effect on C¯l (e.g. upto 5.3% at α = 5) while Re increases both vortex shedding frequency (e.g. 16.8% at α = 1) and heat transfer (e.g. upto 73.3% at α = 1). A flow map in a three-dimensional domain of S*, α and Re is provided, distinguishing steady and unsteady flows. Four distinct flow regimes are labeled, namely steady flow, alternate coshedding (AC) flow, single rotating bluff-body (SRB) flow, and inverted-rotation (IR) flow. An increase in |α| causes a modification of the AC flow to a steady flow and then to a SRB or IR flow