Experimental investigation of temperature and velocity distributions around a cylinder applied with active flow control technique

The character of the flow field changes according to the geometric structure and flow properties of the object that the flow touches. In an uncontrolled flow, flow separation will occur on the bodies and this will cause vortex shedding. The resulting vortexes will cause vibrations on the objects and these vibrations will cause deformations on the object and reduce the service life of the objects. In this study, it is aimed to experimentally investigate the effects of rotating and non-rotating cylinders with different surface geometries on flow and heat transfer. In the study, the effects of the vortex shadings in the trace region and the rollers in the downstream region of the slip layer were investigated by connecting the cylinder in the upstream region to a servo motion system, rotating at a standstill with zero rotational speed and at different rotation speeds. The experiments were carried out in an open water channel over a closed circuit. In the study, independent parameters such as depth-width ratios of surface roughness (ɛ/z), rotational speed (α), Reynolds number (Re), different distance between cylinders in the downstream region of the cylinder in the upper flow region (L/D) and the roughness geometry (square, triangular and circular) effects on heat transfer and flow structure were investigated. At the end of the study, the optimum L/D distance for Re=1400 was determined as L/D = 1, and the optimum L / D distance for Re=2700 and Re=5000 was determined as L/D = 2. Experiments were carried out in this direction. It was seen that the Nusselt number increased with the increase of the Reynolds number. It has been observed that cylinders with different surface roughness do not have a significant effect on heat transfer and flow structure compared to smooth cylinders, but cylinders with rough surfaces compared to smooth cylinders narrow the flow separation point. It has been observed that high rotation speeds have a positive effect on heat transfer and increase the Nusselt number.