The influence the number of holes on effusion cooling effectiveness for an X/D of 4.7

Conjugate heat transfer CFD predictions were made, using ANSYS FLUENT, of the effects of the number of holes per square metre of surface area, N, on effusion overall cooling effectiveness for square array holes with a pitch to diameter ratio, X/D, or 4.7. Nimonic 75 effusion walls 6.35mm thick were modelled at 770K crossflow at 27 m/s with 300K coolant. The computational procedures include the use of a gas tracer to predict the adiabatic film cooling, which was not measured in the hot wall experimental results, as well as the overall cooling effectiveness. The computational results of the overall cooling effectiveness differed from the experimental data by 2–12%, depending on N and G. The results showed that increasing N reduced the amount of coolant air mass flow, necessary to achieve a target overall cooling effectiveness of 0.7, by 50% for 26,910/m2 compared with 9688/m2. With a very low G of 0.18 kg/sm2 the highest N of 26,910/m2 was predicted to have an overall cooling effectiveness of 0.7 compared with 0.55 kg/sm2 for the lowest number of holes, 4306/m2. This is one of the lowest published coolant air mass flows for the design overall cooling effectiveness of 0.7, which gives acceptable metal temperatures under engine combustor conditions.