Optimization of a Novel Design-For-Additive-Manufacturing Film Cooling Hole

Additive Manufacturing has been proving a very interesting potential to produce objects having both tiny dimensions and complex and twisted shapes. For this reason, in the last years, many efforts have been done to employ AM techniques to film cooling technique in the turbine blade cooling field. The aim of the present work is to present a methodology aimed to develop a novel diffusive film cooling hole within the framework of Design-for-Additive-Manufacturing. First, starting from a set of fundamental parameters, the hole has been designed as a result of a numerical optimization in order to find out the best trade-off between different needs. Both the discharge coefficient and the adiabatic effectiveness have been evaluated and compared with the well-established 7-7-7 fan-shaped hole in order to quantify the potential of the novel geometry. Once the numerical procedure ended, one candidate point was selected as the output to be printed by means of a Laser Powder Bed Fusion (LPBF) technique. Flow checks tests were performed on a row of 11 holes per shape and the measured discharge coefficient was found to be far lower than expected. A Computed Tomography analysis showed that the hole internal surfaces and entry/exit section collapsed in some areas. Hence, on the one hand, the numerical procedure and the outcoming shape were validated over an up-scaled flat plate housing the novel holes. Pressure Sensitive Paints measurements were performed in an open-loop wind tunnel for a blowing ratio ranging between 0.25 and 2.00. The adiabatic effectiveness showed a good agreement with CFD data, with the novel hole outperforming the 7-7-7 one. On the other hand, a compensation strategy was developed for the optimized geometries in order to overcome the difficulties encountered by the AM process due to the very tiny dimensions of the hole. After the critical features were identified and fixed by a re-design of the optimized shape, a CFD validation showed a very similar performance compared to first optimization geometry. In the end, the re-designed hole was printed. Flow check tests confirmed a higher discharge coefficient than the original one, while PSP measurements showed an improved effectiveness than the fan-shaped hole.