Conjugate heat transfer CFD predictions of metal wall temperatures with arrays of short holes as used in impingement and effusion cooling

Conjugate heat transfer (CHT) predictions were undertaken for metal walls with arrays of short holes, as used in impingement and effusion cooling. The geometries studied were square arrays of coolant air jet holes of pitch to diameter ratio X/D from 2 - 11, using 10 rows of holes on a 152mm square Nimonic 75 wall that was 6.35mm thick. Previous published work had experimentally measured the surface averaged heat transfer coefficient and pressure and this was the data base against which the CHT-CFD was compared and the most suitable turbulence model determined. Symmetry was assumed in the computations so that only one hole was modelled. Comparison was also made for CHT predictions of the heat transfer for the array of jets used as impingement heat transfer jets with a target flat wall 10mm from the array of jets. The predictions were for classic thermal entry length into a round hole in a metal wall with a hole length to diameter ratio from 0.8 to 4.6. The predictions for the standard k-ε turbulence model were in reasonable agreement with the measurements. More advanced turbulence models had worse agreement with the experimental results than the standard k-ε model with standard wall functions. The overall heat transfer, expressed per wall hole approach surface area, was comparable with impingement heat transfer. This shows how effective the wall internal cooling is for effusion and impingement jet walls.