Large Eddy Simulation of high-Reynolds number flow past a rotating cylinder S.J. Karabelas * National Technical University of Athens (NTUA), Department of Chemical Engineering, Computational Fluid Dynamics Unit, 157 80 Athens, Greece article info Article history: Received 13 May 2009 Received in revised form 15 January 2010 Accepted 9 February 2010 Available online 27 April 2010 Keywords: Magnus effect Rotating cylinder Load stability Turbulence abstract In the present study, uniform flow past a rotating cylinder at Re = 140,000 is computed based on Large Eddy Simulation (LES). The cylinder rotates with different spin ratios varying from a = 0 to a = 2, where a is defined as the ratio of the cylinder’s circumferential speed to the free-stream speed. The Smagorinsky model is applied to resolve the residual stresses. The present commercial code is validated based on avail- able numerical and experimental data. The results agreed fairly well with these data for the cases of the flow over a stationary and over a rotating cylinder. As the spin ratio increases, the mean drag decreases and the mean cross-stream force acting to the cylinder increases. The vortices (time-averaged) down- stream of the cylinder are displaced and deformed and the vortex that is close to the region of the fluid’s acceleration shrinks and eventually collapses. By increasing a, the flow is also stabilized. It is observed that the vortex shedding process is suppressed. Specifically, the flow is unstable in load terms for spin ratios up to 1.3. After this critical value, the flow is transitional for a few dimensionless time units dem- onstrating the well-known von-Karman vortex street and then it becomes stable with almost constant loads. An encouraging outcome resulting from this study is that the LES computations could be accurate for high-Re sub-critical flows with grids of medium resolution combined with a validated sub-grid scale model and a low-diffusive discretization scheme. Ó 2010 Elsevier Inc. All rights reserved. 1. Introduction Bluff body flows have been the target of study for many scientists, since the physics of these flows is very complex and they require spe- cial attention to their modelling and numerical solution. They are also ideal cases for the validation of different approaches to turbu- lence modelling. One of these is Large Eddy Simulation (LES), a prom- ising technique that has recently started to gain popularity even for high-Re flows. However, it is well known that for high-Re regimes the sub-grid-scale and the near-wall modelling become crucial for the accuracy of the computations. In cylinder flows, the results are not very promising for super-critical Re numbers, at least based on the preliminary study by Catalano et al. (2003) who assessed the validity of LES with near-wall modelling for a flow past a circular cylinder up to Re =2  10 6 . Their results departed significantly from those re- ported in experiments. Nevertheless, they stated that their study is at a preliminary stage and no well-justified conclusions could be drawn. In contrast, the numerical results for sub-critical but still high-Re flows past a cylinder are satisfactory. Breuer (1999, 2000) conducted relevant studies at Re = 140,000, where he found suffi- cient agreement with the well-organized experiment of Cantwell and Coles (1983). Elmiligui et al. (2004) studied the same problem at Re = 50,000 and Re = 140,000, but the free-stream flow was not laminar. Medium turbulence intensity was imposed on the inlet of the domain. The results were quite different from those of Breuer (2000) in terms of the drag coefficient and Strouhal number, but they agreed well with the numerical experiments of Travin et al. (2000) and Hansen and Forsythe (2003), who used relevant boundary and initial conditions. The above studies cited in the open literature refer to the mod- elling of the flow past a stationary cylinder for high-Re numbers. The more challenging case of the flow past a rotating cylinder has not yet been investigated extensively. In the laminar regimes two highlighted studies are those of Mittal and Kumar (2003) and Padrino and Joseph (2006). The Re number based on the diam- eter of the cylinder and the free-stream flow is 200 in the first study and 200, 400 and 1000 in the latter study. In the context of these articles, the physics of the laminar flow past a spinning cyl- inder is analysed for various spin ratios whereas the lift, drag and pressure coefficients are computed. The well-known Magnus effect is examined in this framework and the results (for the lift force) are compared with those of potential flow (Zdravkovich 1997). An interesting study of Stojkovic et al. (2002) has been also found in the literature, in which high rotation rate effects to the mean loads are investigated. The values of a varied from 0 to 12 and the char- acteristic Re number based on the diameter of the cylinder was 100. Many additional results have been obtained, including the frequencies of the wake instability and the distinct changes of the flow structure. The load stability of laminar flows has also re- ceived considerable attention. It has been generally found in the preceding studies that the rotational effects suppress the vortex 0142-727X/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.ijheatfluidflow.2010.02.010 * Tel.: +306 977207390. E-mail addresses: stkarabelas@gmail.com, stkarabelas@yahoo.gr International Journal of Heat and Fluid Flow 31 (2010) 518–527 Contents lists available at ScienceDirect International Journal of Heat and Fluid Flow journal homepage: www.elsevier.com/locate/ijhff