Flat Wall Cooling Aerodynamics and the Effects of Cross-flow in the Impingement Gap with Single Sided Air Jet Exit Flow using CHT CFD Predictions

Flat wall impingement cooling investigation was carried out using combined numerical analyses of conjugate heat transfer (CHT) and computational fluid dynamics (CFD) techniques. The analyses were undertaken in impingement array of jet holes with self-induced cross-flow in the impingement gap using a single sided flow exit geometrical model. The aim is to understand the aerodynamics interaction that results to the deterioration of heat transfer with axial distance, as the addition of duct flow heat transfer would be expected to lead to an increase in heat transfer with axial distance. A square array of impingement jet holes was used for a common geometry investigated experimentally, pitch to diameter ratio X/D of 5.0 and impingement gap to diameter ratio Z/D of 3.3 for 11 rows of holes in the cross-flow direction.  A metal duct wall was used as the impingement surface with a 100 kW/m2 imposed heat flux. For a gas turbine combustor cooling application operating at steady state with a temperature difference of ~ 450 K, this heat flux corresponds to a convective heat transfer coefficient (HTC) of ~ 200 W/m2K.  A key feature of the predicted aerodynamics was recirculation in the plane of the impingement jets normal to the cross-flow, which produced heating of the impingement jet wall. This reverse flow jet was deflected by the cross-flow, which had its peak velocity in the plane between the high velocity impingement jets. The cross-flow interaction with the impingement jets reduced the interaction between the jets on the surface, with lower surface turbulence (TKE) as a result and this reduced the surface HTC. A significant feature of the predictions was the interaction of the cross-flow with the impingement jet wall and associated heat transfer to that wall. The results showed that the deterioration in heat transfer with axial distance was well predicted together with predictions of the impingement gap exit pressure loss