International Journal of Thermal Sciences 155 (2020) 106453 Available online 30 April 2020 1290-0729/© 2020 Elsevier Masson SAS. All rights reserved. Thermal buoyancy effects on the fow feld and heat transfer of a rotating cylinder: A numerical study Erfan Salimipour Department of Mechanical Engineering, Quchan University of Technology, Quchan, Iran A R T I C L E INFO Keywords: Rotating cylinder Buoyancy Flow pattern Lift coeffcient Drag coeffcient Nusselt number ABSTRACT The present paper numerically investigates the laminar, two-dimensional and horizontal fow around a hori- zontal isothermal rotating cylinder under the buoyancy effect. To study the buoyancy effect, a range of Grashof numbers from 0 to 12 � 10 4 is used, and to check the effect of the cylinder rotation, the ratio of the rotational speed to the free-stream velocity between 4.5 and 4.5 is applied. The simulation is carried out at the Reynolds number of 200 and the Prandtl number of 0.7. To simulate the fuid fow, the Navier-Stokes equations are numerically solved using a fnite-volume scheme. Results show that the interaction of the main stream with the rotation and buoyancy can alter the fow feld and heat transfer characteristics such as fow pattern, surface pressure distribution, lift and drag coeffcients, and Nusselt number. The clockwise (cw) rotation decreases the amplitude of oscillations in the fow compared to the counterclockwise (ccw) rotation. In ccw rotation, as the Grashof number increases, the mean lift coeffcient increases; while in cw rotation, increase in the Grashof number reduces the mean lift coeffcient. Moreover, in terms of Grashof numbers ranging between 8 � 10 4 and 12 � 10 4 , the Nusselt number is almost unchanged. 1. Introduction When a circular cylinder exposed to a uniform stream rotates, an asymmetric secondary fow is created around it. This asymmetric fow causes the pressure difference between the top and bottom surfaces of the cylinder, which leads to the generation of the lift force on the cyl- inder [1]. This generated force can have a variety of applications such as a ship sail, a means for fow control as well as in Magnus wind turbines. The fow around stationary cylinder itself has a considerable complexity due to the vortex shedding behind the cylinder. The cylinder rotation increases this complexity by creating a secondary fow. Numerous research studies have been carried out on the fow past rotating cylinder and its aerodynamic forces [2–8]. Moreover, if the buoyancy effects are also added to the fow around the rotating cylinder, the complexity of the fow and heat transfer will increase. In such a case, the fnal fow is a combination of three fows such as freestream, fow due to the cylinder rotation, and fow due to the buoyancy. This is important in addition to engineering applications such as defrosting the Magnus wind turbines, in terms of fow physics and heat transfer. Research studies have shown that this fow can be investigated in various respects. Michaux and B� elorgey [9] experimentally analyzed the effects of the fow separation of a cylinder with viscosity-buoyancy interaction for different Reynolds numbers. According to their experiments, for the Richardson numbers less than 0.5, the forced convection and for the Richardson numbers greater than 0.5, the free convection heat transfer predominates. Mo- rales et al. [10] simulated the fow and mixed convection heat transfer around a rotating cylinder in a range of Rayleigh numbers between 10 3 and 10 8 and Reynolds numbers between 0 and 557 using the Large Eddy Simulation (LES) method. Furthermore, Soong [11] studied the effects of thermal buoyancy on non-isothermal rotational fows using a numerical simulation. Ghazanfarian and Nobari [12] investigated the fow and convection heat transfer characteristics of the fow past a rotating cyl- inder with vertical oscillations for the Reynolds numbers of 50, 100, and 200, speed ratios between 0 and 2.5, and Prandtl numbers of 0.7, 6, and 20. They observed that as the cylinder speed ratio increased, the Nusselt number and drag coeffcient decreased. Moreover, Paramane and Sharma [13] studied the fow and heat transfer from a rotating circular cylinder with uniform heat fux in terms of Reynolds numbers ranging from 20 to 160 and speed ratios between 0 and 6. They proposed a relation to calculate the heat transfer in the laminar fow regime. In addition, Liao and Lin [14] numerically studied the fow and mixed convection heat transfer of a heated spinning cylinder enclosed in a square enclosure in a range of Rayleigh numbers between 10 4 and 10 6 and Prandtl numbers from 0.07 to 7. Their results showed that the E-mail addresses: esalimipour@qiet.ac.ir, erfan.salimipour@gmail.com. Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: http://www.elsevier.com/locate/ijts https://doi.org/10.1016/j.ijthermalsci.2020.106453 Received 4 November 2019; Received in revised form 22 March 2020; Accepted 23 April 2020