Our research is motivated by one of the current challenges of the turbomachinery industry, which consists of increasing the turbine entry temperature of the engines to increase thermodynamic efficiency and hence reduce fuel consumption. Consequently, critical engine components such as the turbine blades need to be designed to withstand even higher temperatures, which surpass the melting point of the metal alloys they are constructed of. Hence, turbine blades are fitted with an internal cooling system, which bypasses lower temperature air from the compressor directly into the turbine blades. This cold air injection forms rows of cold round jets which impinge onto the outer wall of the turbine blade, reducing its temperature. Due to the complexity of the problem, previous studies have mainly focused on single jet impingement cooling, where such setup is far from the flow conditions present in a real engine. Unfortunately, the flow physics of more complex multi-jet setups are not fully understood yet, limiting the efficiency of the cooling system design. Therefore, to shed light into the physical mechanisms behind impingement cooling at realistic engine conditions, we present a high-fidelity dataset of several multi-jet impingement setups using different inter-jet distances and cross-flow conditions. The parameter space across which we investigate the jet spacing effect ranges from 5 to 15 jet diameters, with intervals of 5 jet diameters. Our results show that larger jet spacings achieve lower heat-transfer efficiency values at the stagnation point on all jets, where the minimum heat-transfer efficiency decreases non-linearly as a function of the jet spacing. On the other hand, the maximum heat-transfer efficiency scales linearly with the inter-jet spacing. The effect of cross-flow on the heat-transfer efficiency at the impingement wall is investigated for a setup with an inter-jet distance of 10 jet diameters. The cross-flow magnitudes investigated are 20 and 40% of the bulk velocity of a single jet. Comparing these different setups shows that lower cross-flow values significantly enhance the maximum heat-transfer efficiency. In contrast, a cross-flow of 40% is found to reduce the intensity of the jet impingement, which leads to a much lower maximum heat-transfer efficiency. This suggests that the optimum cross-flow magnitude lays between 20 and 40%. The influence of the boundary conditions used for the cross-flow cases is assessed by running additional simulations with a turbulent inflow. The results from these simulations show that the effect of the inflow turbulence is minimal for the 20% case, and it causes a reduction in the heat-transfer efficiency for the 40% case. Through a direct comparison of these multi-jet results with the heat-transfer data from a single-jet simulation, we show how accounting for these more complex engine-like conditions can be critical to achieving a correct heat-transfer prediction for this problem.


High-Fidelity Simulations of Multi-Jet Impingement Cooling Flows

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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