Experiments on heat transfer and film cooling characteristics of double-wall cooling structure with novel slot holes and pin-fins

The influences of blowing ratio, mainstream velocity, density ratio and jet Reynolds number on the heat transfer and film cooling properties of double-wall cooling cell (DWCC) with slot holes, impingement and diamond-shaped pin-fins were studied by means of pressure sensitive paint and transient liquid crystal. The simulation obtained the flow characteristic at a jet Reynolds number of 20000. The results indicated that with the increase of blowing ratio, the film cooling performance of DWCC structure also increased, and there was no film lift-off phenomenon which occurred in the cylindrical hole. The presence of pin-fins created a spike-shaped film in the slot outlet. Therefore, when studying the DWCC structure, it was important to consider the couple effects of impingement, pin-fins, and slot hole. As the density ratio decreased and the mainstream velocity increased, the film cooling effectiveness (FCE) gradually decreased. When jet Reynolds number increased from 20,000 to 60,000 under a density ratio of 2.0, the area-averaged FCE increased from 0.308 to 0.435, with an increase of up to 41.2%. The convective heat transfer level of impingement stagnation point was much higher than that of pin-fins region. Due to the transition between the impinging jet and the wall jet, the heat transfer coefficient (HTC) had a multi-peak distribution. In addition, several low heat transfer zones similar to wing-shaped, eye-shaped, and crescent-shaped were observed on the target surface and bottom surface inside the cooling cell. The DWCC structure studied in this paper is more efficient in cooling performance compared to traditional cooling structures. This makes it suitable for use in various fields such as heat transfer of turbine blades and electrical equipment.