Mixed Convective Transport around Counter Rotating Tandem Cylinders at Low Reynolds Number

Abstract

Rotating an object in a flowing fluid brings stability to the flow around the object. Consequently, an inherently unsteady flow may be degenerated into a steady pattern. On the contrary, cross thermal buoyancy brings instability to the flow causing triggering of vortex shedding even at relatively low Reynolds numbers. Hence, rotation and cross buoyancy produces opposing effects in this context. Furthermore, multiple objects in a flowing fluid develop intriguing wake dynamics following their interference effects. When tandem cylinders are placed in a flowing stream, depending on the gap between them, the vortex shedding may get triggered. These physical behaviors are coupled in this work to understand the simultaneous effect of rotation, cross thermal buoyancy (Richardson number, 0–1) and cylinder gap spacing (0.2–3) on the wake dynamics around tandem circular cylinders at Reynolds number 100 and Prandtl number 0.71. It is observed that at a critical rotational speed, the unsteady periodic flow is transfigured to a steady pattern. At smaller gap spacings (0.2, 0.7), a higher rotational speed is required particularly at higher strengths of buoyancy (0.5, 1) to control the flow instabilities and suppress the vortex shedding. The critical rotational speed is maximum at gap spacing of 0.2 for the highest buoyancy strength. Furthermore, the critical rotational speed reduces as the gap spacing increases.