Near-wake effects of a heat input on the vortex-shedding mechanism R. Kieft * , C.C.M. Rindt, A.A. van Steenhoven Faculty of Mechanical Engineering, Eindhoven University of Technology, P.O. Box 513, Eindhoven 5600 MB, The Netherlands Received 19 June 2005; received in revised form 5 March 2007; accepted 16 March 2007 Available online 10 May 2007 Abstract This article presents the investigation on the vortex formation and shedding process behind a heated cylinder which is exposed to a cold cross flow. The Reynolds number is chosen to be 75 while the Grashof number is varied between 0 and 5000 (resulting in a variation from forced to mixed convection). The numerical results show that the addition of heat disturbs the vortex formation process. The vor- tices shed from the upper half of the cylinder become stronger for increasing heat input. Therefore, the shedding process at the upper half of the cylinder becomes more effective compared with the process at the lower half. Consequently, the vortices shed from the upper half of the cylinder have a higher vorticity extreme and a higher temperature. The results show that the difference in effectiveness is mainly caused by a decreasing effect of strain rate during the formation of an upper vortex. This change in strain rate is caused by a change in flow pattern around the cylinder for increasing Grashof number. For higher heat input more fluid flows underneath the cylinder, result- ing in weaker shear layers at the upper part of the cylinder. Ó 2007 Elsevier Inc. All rights reserved. Keywords: Vortex-shedding; Heat; Spectral element model; Cylinder 1. Introduction and problem definition The process of vortex-shedding behind obstacles has been the topic in many fundamental investigations for over several decades. Insight in the complicated process of vor- tex structure formation and shedding will lead to a better understanding of wake processes as mixing and transition to turbulence, which are of interest from a more practical point of view. For example, in heat transfer units or during cooling of electronic equipment wakes are created behind the heated components. These wakes will have an influence on the performance of downstream components. Especially for these non-adiabatic cases, the influence of heat on the vortex-shedding process can have a strong effect on the wake behaviour. The induced heat, for example from dissi- pating electronic components, will give rise to a buoyant flow. Therefore, the generation of vorticity as well as the formation of a coherent vortex structure will differ from the adiabatic situation and it is expected that the wake characteristics will change, occasionally leading to an early transition to turbulence (Kieft, 2000). So far, the effect of heat on the vortex formation and shedding process has not been studied intensively. In the early seventies, some interest arose in the effect of heat on the wake behaviour behind a heated cylinder, initiated by the interest in the performance and accuracy of hot wire anemometry. More detailed studies on the effect of heat on a vertically upward wake flow are presented in Noto and Matsumoto (1987) and Badr (1984). These numerical stud- ies show that both the production of vorticity as well as the formation of a vortex structure are influenced by increasing the temperature of the cylinder behind which the wake is formed. By increasing the temperature the vortex-shedding process can even be suppressed. These results were later experimentally verified in Michaux-Leblond and Be ´lorgey (1997). However, the effect of heat on the actual vortex for- 0142-727X/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.ijheatfluidflow.2007.03.002 * Corresponding author. Address: Corus Research Development & Technology, P.O. Box 10000, IJmuiden, 1970 CA, The Netherlands. Tel.: +31 251497553; fax: +31 251470265. E-mail address: rene.kieft@corusgroup.com (R. Kieft). www.elsevier.com/locate/ijhff International Journal of Heat and Fluid Flow 28 (2007) 938–947