Enhancement of heat transfer and reduction of drag of a circular cylinder (flow control using a small rod)

Abstract

A small rod was set upstream of a circular cylinder for enhancement of heat transfer and reduction of drag of the circular cylinder. The diameter of the cylinder D was 40 mm, and that of the rod d was varied from 1 to 12 mm. The distance between the axes of the cylinder and rod L was varied from 50 to 120 mm, and Reynolds number ranged from 1.5 × 104 to 6.2 × 104. The local heat transfer distribution has a maximum at the angle of ± 30 ≈ 35° from the front stagnation point, regardless of the presence or absence of vortex shedding from the rod. Therefore, the heat transfer at the front face increases markedly. Beyond Re ≥ 3.1 × 104, a second maximum of heat transfer appears at φ = ±110° upon transition to turbulent flow. In the separated region at the rear face, the heat transfer decreases. The overall heat transfer increases with an increase in d/D and a decrease in L/D. This method is useful for higher Reynolds numbers. The optimum conditions are d/D=0.25 and L/D=1.25, that is, the case in which quasi-stationary vortices are formed between the rod and the cylinder. In this case, the overall heat transfer increases by 40%, and the total drag coefficient included the drag of the rod is reduced by 43% compared to that of without the rod.