Effect of internal crossflow on impingement cooling flow and heat transfer characteristics

The flow and heat transfer characteristics of a single-row impingement jet, fed by internal crossflow, are numerically investigated. The results showed that the internal crossflow propels a rapid coolant outflow on the leeward side of the hole, subsequently elevating the local impingement Reynolds number. Concurrently, the internal crossflow augments the heat transfer rate on the impingement target surface, with surges reaching up to 60 % in the local Nu number and 11 % in the average Nu number at low external crossflow. Counter-intuitively, the heat transfer enhancement due to the increase in local Reynolds number diminishes as the strength of the external crossflow increases. This phenomenon is attributed to the emergence of an in-hole counter-rotating vortex pair, whose interaction with the external crossflow induces elongation of the jet in the pitchwise direction. However, these enhancements in heat transfer rate are counterbalanced come at the expense of a more complex flow structure and higher flow losses. The weight of the internal and external crossflow on impingement cooling performance is also investigated using the overall thermal efficiency which considers both heat transfer and flow resistance and it is found that the external crossflow is the main culprit for the decrease in overall thermal efficiency.