Additively Manufactured Porous Geometries for Hybrid Turbine Cooling

Abstract

Discrete film cooling holes are limited by subtractive manufacturing techniques and experience depreciating performance when operating above critical velocity ratios. This study introduces an alternative method of bringing coolant to the surface of the blade via finite strips of porous material interlaced throughout the blade, made possible by advances in additive manufacturing (AM). Both experimental and computational studies were performed on the porous hybrid configuration to characterize downstream and off-wall performance, where experimental adiabatic effectiveness values were achieved using a plastic, fused deposition printed lattice structure. The method of bringing coolant onto the surface of the blade through an additively manufactured porous region experienced downstream adiabatic effectiveness values similar to slots while providing better structural stability. Additionally, the hybrid configuration outperformed shaped film cooling holes by injecting an ultra-thin layer of coolant that was evenly distributed span-wise across the blade. When operating at VRhybrid = 0.052 and L/d = 2 the hybrid configuration produced spatially averaged values 30% greater than the shaped holes while using equivalent coolant mass flow rate. Also, for an L/d = 10, the spatially averaged adiabatic effectiveness, for the hybrid configuration, is a factor of three greater than for shaped film cooling holes, while requiring a five times greater coolant mass flow rate. Finally, the RANS computational model accurately predicted downstream effectiveness values, at low velocity ratios, within experimental uncertainty but showed inaccuracies when predicting off wall effectiveness values and at higher velocity ratios.