Conjugate Heat Transfer CFD Predictions of the Influence of the Impingement Gap on the Effect of Crossflow

This conjugate heat transfer (CHT) CFD predictions were carried out for a square array impingement holes with X/D of 5 and at a single high mass flow cooling rate G of 1.84kg/sm²bar. CHT was modelled with a 100kW/m² fixed heat flux imposed at the hot face of the target wall, which gives a temperature at the cold face that is typical of normal operating conditions of a gas turbine. The wall temperatures as a function of distance along the gap and through the wall thickness were computed, together with the gap aerodynamics. The main parameter investigated was the gap Z/D (0.83–7.0). The results showed that the surface averaged Nu/Pr^0.33 was predicted to be reduced from 73 to 48 over the range of Z/D, which is in good agreement with literature values. The cause was shown to be reduced surface turbulence levels as the crossflow convected turbulence away from the surface. There was also heating of the impingement jets at large Z/D so that the original cool jet air did not reach the surface.