科研之友
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摘要
Numerical simulations and experimental study were carried out to investigate the flow and heat transfer characteristics of air flowing across different types of oval-shaped cylinders, for Reynolds numbers varying from 4000 to 50,000. These cylinders have axis ratios, e, of 1, 1.5, 2, 3, 4, and 5 with the major axis parallel to the free-stream. Numerical results show the closer the distance to mainstream, the smaller the local velocity gradient is. The angular position of the minimum value of C-p decreases as e decreases and the maximum value of C-f gradually increases with e increasing. 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. Based on the presented results, it can be emphasized that the average heat transfer coefficient firstly increases and then decreases by increasing the axis ratio of the tube, implying that the elliptical tubes with a suitable axis ratio possess more advantages over circular tubes. Comparisons of the numerical results with the existing data verify the validation of the present study.
