Research On Flow And Heat Transfer Characteristics Of Impingement With Initial Cross-flow In Narrow Spaces

The cooling system design of the gas turbine has been always the most important part of the advanced engine research. With the improvement of the modern manufacture techniques, the cooling structure becomes more complex, such as impingement in narrow spaces and in multi-angles. The numerical simulation and experiment were conducted to investigate the flow and heat transfer characteristics of impingement cooling structure in narrow spaces, which the ratio of the channel height to the diameter of impinging hole ( z n/d ) is smaller than 1. Some influential parameters were considered, such as jet Reynolds number (3000< Re j <10000), nozzle-to -plate distance (0.6< z n/d <2.0), initial cross-flow (0< Gc /G j<0.3) and jet-to-jet distance (2< xn /d <6).Firstly, the flow field indicates that: there is an obvious pressure difference between the upstream and downstream region of jet-flow channel, which results in the unevenness of mass-flow quantum. The interaction of the multi jet streams leads to the formation of complex vortical structures that govern heat removal from the impinging surface. In the section along with the outflow direction, there is only one vortex upstream the stagnation region and it becomes smaller even disappered near the outlet. The vortex couple exists in the vertical plane of jet flow channel.Then, local Nusselt numbers are evaluated on the specified lines located on the surface. The heat transfer on the upstream impinging target plate is better than downstream areas under the condition of narrow spaces. The heat transfer enhances clearly with the increase of the jet Reynolds number. Because of the initial cross-flow, the local Nusselt numbers decrease and do not show the secondary maxima at all. The cross-flow also pulls off the stagnation point downstream and the influent is significant in the regular nozzle-target distance. Changing jet-to-jet distance significantly affects the heat transfer process near the surface. Specifically, increasing the jet-to-jet distance can improve the heat transfer coefficient.As a conclusion from the simulation and experiment results, the flow and heat transfer characteristics of jet array impingement in narrow spaces are determined by parameters both flowing and geometrical, which is not as the same as in regular impinging spaces. So it must be considered comprehensively in order to obtain the ideal cooling effect.