Combined film and impingement cooling of flat plate with reverse cooling hole

Abstract

• Performance of combined impingement-film cooling is analyzed for a flat plate. • Effectiveness and pressure drop are compared for forward and reverse injections. • Effectiveness is found to be lower for the reverse injection at lower blowing ratio. • Contrary effect of cooling hole orientation is noticed at higher blowing ratio. • Pressure drop is also lower in case of the reverse orientation of the cooling hole. A numerical model is developed in the present work for analysing cooling performance of combined impingement-film cooling under realistic engine operating conditions. Effect of jet impingement along with the film cooling is analysed on fluid flow, heat transfer, cooling performance and pressure drop for forward and reverse orientations of the cooling hole. Further, effect of hole orientation on the cooling performance is studied under wide range of blowing ratios and jet-to-plate spacings. It is observed that the effect of jet impingement is significant on the cooling performance. Surface temperature of the metallic plate is found to be 50–90 °C lower for the combined jet impingement and film cooling case as compared to the only film cooling case. The improvement in the heat transfer for combined impingement-film cooling is at the cost of increased pressure drop. Film cooling effectiveness for the case of combined impingement-film cooling is found to be dependent on the hole orientation and blowing ratio. The secondary jet penetration into the mainstream increases with increase in the blowing ratio/velocity ratio. Kidney-vortices are formed at a velocity ratio of 1.07 from forward injection which resulted in decreased film cooling effectiveness. These kidney-vortices were not formed for the case of reverse injection and coolant spreads uniformly in the transverse direction. At lower velocity ratios when formation of kidney vortices is not prominent, forward injection results in better film cooling effectiveness compared to the reverse injection. Gas radiation is also considered in the modelling and its effect is found significant on the temperature prediction of the components.