Study on flow structure and heat transfer characteristics of a novel double layer heat shield in an afterburner

In this study, a novel double-layer heat shield structure consisting of a flat impingement plate and a longitudinal rippled film plate has been proposed to save the cooling air and to improve the cooling effectiveness simultaneously. In this paper, a series of numerical calculations have been carried out to investigate the effects of parameters including impingement distance (Hi/di), opening rate and Gc value (the cooling air flow rate in unit area) on the flow and heat transfer characteristics and cooling effectiveness. Furthermore, the values of overall cooling effectiveness of three structures, namely, the present structure, single-layer ripple structure and doublelayer flat structure, have been compared under the equal cooling air flow rate. The results show that, as the impingement distance increases, the cooling effectiveness on the gas side surface decreases, but the surface temperature uniformity shows first increasing by 4.2 % and then decreasing by 2.3 %. The impingement distance of 12d(i) similar to 15d(i) achieved a better cooling effectiveness for the novel structure. The decrease of the holes spacing in the streamwise direction improves the low wave peak cooling effect zone and the upstream zone. The decrease of the holes spacing in the spanwise direction plays a more important role in the downstream zone. When the Gc > 0.5, the overall cooling effectiveness of the present novel structure is better than that of double-layer flat plate heat shield.