Experimental and numerical study of heat transfer and pressure loss in a multi-convergent swirl tube with tangential jets

Abstract

This paper presents a comparative experimental and numerical study of heat transfer and pressure loss in a swirl cooling system with multi-convergent tubes. The results are compared with those of a baseline circular swirl tube. The two swirl tubes are both with multiple tangential jet slots, which can induce large-scale swirling flows and significantly enhance the convective heat transfer. The multi-convergent swirl tube can be considered as an effective internal cooling method for the gas turbine blade leading edge. Transient liquid crystal thermography is used to obtain detailed heat transfer distributions on the internal surfaces of the two swirl tubes. It is shown that through a small change in the swirl tube structure the heat transfer rates and uniformity could be significantly improved in the multi-convergent swirl tube. In more detail, the heat transfer of the multi-convergent swirl tube reaches peak values under the jet slots, and then decays more slowly than the baseline swirl tube. After the third jet, the heat transfer of the convergent sections between the inlet jets keep almost stable along the axial direction, since the convergent structures restrain the decay of swirl intensity. Besides, the multi-convergent structure offers a swirl tube with the ability to better resist against the cross flow, which guides the upstream swirling flow to the downstream tube core, avoiding the collision and mixing between the cross flow and the downstream wall jet flow, thus improving the heat transfer rates. Compared with the baseline swirl tube, the experimental globally averaged Nusselt numbers of the multi-convergent swirl tube can be increased by 11.8%-23.3% for the Reynolds number range of 10,000 to 40,000. As a supplement to the experiments, three-dimensional numerical computations provide more insights into the turbulent flow structure in the two kinds of swirl tubes.