Metallic Materials by Additive Manufacturing for Surface Cooling of Combustion Chambers

The cooling of metal parts is an advanced key-research in aeronautics, especially for turbine blades and engine combustion chambers. To protect the walls directly exposed to the hot flow, the solution currently used is film cooling: a fraction of the cool air coming from the compressor is injected through the perforated wall, leading to a protective film on the hot surface.

Thanks to new additive manufacturing technologies, such as the Electron Beam Melting (EBM) used in this study, we are able to design complex hole geometries that cannot be manufactured by more conventional technologies. Our goal is to improve the cooling efficiency by increasing internal heat exchanges.

Multi-perforated walls are redesigned: a second network of holes interconnecting the through ones along one row or a 3D pattern is added. The idea is to cool the space between the through holes by diverting a fraction of the cool flow in this second network. A main technological issue is to remove the remaining powder in the holes, slightly sintered during the process: different powder removal techniques are investigated.

First aero-thermal simulations are performed in order to start quantifying the cooling efficiency of our solutions and comparing them to the classical multi-perforated wall. A coupled calculation that includes heat transfer between the fluid and the solid helps us evaluating the establishment of the film and the efficiency of the second network of holes.

Moreover, in order to enhance heat exchanges in the wall, the possibility of manufacturing a porous material by EBM is also investigated. Decreasing the intensity of the beam and increasing the scan speed leads to a low energy input to the powder: the resulting permeable microstructure is induced by the network of spaces between interconnected powder grains. Within a well-determined range of parameters, different structures are manufactured and characterized.