Numerical simulation and experimental study were carried out to investigate the flow and heat transfer characteristics of air flowing across different types of oval-shaped cylinders. These cylinders have axis ratios, ε, of 1, 1.5, 2, 3, 4, and 5 with the major axis parallel to the free-stream for Reynolds numbers, based on the hydraulic diameter, varying from 4000 to50000. When ε = 1 the tube is a circular cylinder and when 1/ε = 0 a flat plate is represented. Numerical results show that the wake size decreases as ε increases from 1 to 5. The minimum value of Cp takes place at an angular position decrease as ε decreases and the maximum value of Cf gradually increases with the increasing ε. Simulated results agree very well with those available in the existing literature. Oval-shaped cylinders have a higher favorable pressure gradient at the front of the cylinder and a lower adverse pressure gradient at the back of the cylinder for flows in inhibiting separation. Empirical correlations for each tube have been obtained by numerical simulation relating the dimensionless heat transfer coefficient with the Reynolds Number and Prandtl Number. Field synergy theory and performance evaluation criteria (PEC) were used to analyze the mechanisms of heat transfer enhancement for oval-shaped cylinders. It was found that an oval-shaped tube with ε = 2 has the best comprehensive heat transfer performance at Re >11952. In order to verify the effectiveness and correctness of our numerical model, an experiment was carried out for cylinders for values of ε equal to 1, 2, 3 and 4.
Unsteady Boundary Layers Over Rotating Blades
