Effect of Jet Shape of Square Array of Multi-Impinging Jets on Heat Transfer

It is necessary to increase turbine inlet temperature to improve the performance of the aircraft gas turbine engine. Therefore, effective cooling techniques are still required. The purpose of the present study is to clarify the heat transfer characteristics for the high cooling performance of multiple impinging jets. A focus is placed on the effect of the jet ejection shape, since the shape of jet is expected to enhance flow mixing in accordance with a change in vortex structures at the shear layer of the jet. Experiment was made on the wall jet interaction between adjacent impinging jets by changing the jet ejection shape. Both heat transfer and aerodynamic characteristics in 3×3 square arrays of three types of jet hole shapes, which are circle, cross-shape and oblique cross-shape, are investigated at jet diameter Reynolds number of 4,680. Injection distance is ranged from 2D to 6D, and jet-to-jet spacing is 6D where D is a jet hole diameter. Steady state thermochromic liquid crystal technique is employed to measure local and area averaged Nusselt number. A micro flow sensor, which can detect both flow direction and flow intermittency near the wall, is used to clarify the characteristics of the unsteady flow behavior. It is found that higher local Nusselt number area is spread outward in the concave direction of the cross-shaped jet on the target surface. Characteristic flow behavior due to the flow intermittency and the local flow fluctuation induced by the effect of jet shape are observed in the region surrounded by the adjacent impinging jets in the cases of cross-shaped jet and oblique cross-shaped jet. This intermittent flow phenomenon is considered to contribute to the enhancement of the heat transfer in the intermediate region enclosed by surrounded impinging jets.