Open Access. © 2022 H. Shakir Majdi et al., published by De Gruyter. This work is licensed under the Creative Commons Attribution 4.0 License Curved and Layer. Struct. 2022; 9:81–95 Research Article Hasan Shakir Majdi, Mahmoud A. Mashkour, Laith Jaafer Habeeb*, and Marko Ilic Mixed convection around a circular cylinder in a buoyancy-assisting flow https://doi.org/10.1515/cls-2022-0008 Received Oct 05, 2021; accepted Nov 29, 2021 Abstract: In this paper, the effect of mixed convection on the flow behavior and heat transfer around a circular cylinder disclosed to a vertically upward laminar air stream is numer- ically examine. The buoyancy-aided flow is utilized to elim- inate and control the vortex shedding of the cylinder. The influence of the Grashof number, 0 ≤ Gr ≤ 6000, the flow and thermal patterns, as well as the local and mean Nus- selt number, is investigated at a constant Reynolds number of 100. The unsteady Navier-Stokes’s equations are solved employing a finite-volume method to simulate numerically the velocity and temperature fields in time and space. The results showed periodic instability in the flow and thermal fields for a range of Grashof number Gr ≤ 1300. Also, there is critical value of Grashof number for stopping this instabil- ity and the vortex shedding formed behind the cylinder, by the effect of heating. Thus, by increasing Grashof number between 1400 ≤ Gr ≤ 4000, the periodic flow vanishes and converts into steady flow with twin eddies attached to the cylinder from the back. Furthermore, as Grashof number increases behind Gr ≥ 5000, the flow becomes completely attached to the cylinder surface without any separation. Keywords: Mixed convection, circular cylinder, vortex shed- ding, adding flows 1 Introduction Vortex shedding behind cylinders is an interesting topic for many researchers. This is due to that forming vortex shed- *Corresponding Author: Laith Jaafer Habeeb: Training and Workshop Center, University of Technology, Baghdad, Iraq; Email: Laith.J.Habeeb@uotechnology.edu.iq Hasan Shakir Majdi: Department of Chemical Engineering and Petroleum Industries, Al-Mustaqbal University College, Hillah, Babil, Iraq Mahmoud A. Mashkour: Mechanical Engineering Department, University of Technology, Baghdad, Iraq Marko Ilic: Faculty of Mechanical Engineering, University of Nis, Nis, Serbia ding behind these bodies causes unfavorable oscillations in the aero- or hydro-dynamic loads, leading to undesir- able vibrations in the bodies’ structures. Therefore, a huge effort has been assigned in an attempt to reduce or elimi- nate the effect of vortex shedding. The literature shows that there are various methods to eliminate or control the vortex shedding like suction, blowing, rotating the body, surface roughness, and heating the cylinder, see for example [1–5]. Indeed, this phenomenon in mixed convective flow can lead to very intricate physical circumstances due to the high interaction amongst the buoyancy effects of free convec- tion, effects of forced flow, and the effects of secondary flows generated behind the solid bodies. Many works have discussed this problem. Badr [6] investigated the mixed convective flow and heat transfer about a horizontal cylin- der for contra and parallel flows for Reynolds numbers less than 40. Chang and Sa [7] also investigated the flow behavior, Nusselt number variations, and drag coefficient from a cylinder at Reynolds numbers of 100 and Grashof number between104 for cooling and 104 for heating. It was found that the vortex shedding can be stopped by increas- ing Grashof number higher than 1500. In addition, Wang [8] studied mixed convection from an isothermal needle con- taining a hot tip for contra and assisting flows. Michaux and B’elorgey [9] performed some experiments to study the effect of buoyancy forces of mixed convection on the wake flow behavior behind a circular cylinder the Reynolds numbers of greater than 130. They observed that the forced convection is predominant when Richardson number is higher than 0.5, while the natural convection becomes the dominant for Richardson number less than 0.5. Varaprasad et al. [10] examined the effect of buoyancy forces on the mixed convective flow over a circular cylinder and tested its impact on Nusselt number distributions, drag coefficient, wake structure, and Strouhal number. They reported that the increase in Grashof number could also increase the drag coefficient around the cylinder. Moreover, Kieft et al. [11] investigated the flow wake structure backward a heated cylinder located in a hori- zontal crossflow at constant Reynolds number of 75 and Richardson number ranging between 0 and 1. They found that the heating of cylinder produces vortex shedding in the