PhD grant from LABEX CEMAM 2013-16 in collaboration with ONERA (The french aerospace lab)
The cooling of metal parts is a key advanced research in aeronautics, especially for turbine blades and engine combustion chambers. By making the cooling more efficient, it is possible to reduce the amount of air used or work at higher temperatures and therefore, in all cases, improve engine performance.
To protect the walls directly exposed to the flow, different solutions are used such as the implementation of cooling channels near the exposed surfaces, the addition of thermal barriers, or the "film cooling" solution that insulates the walls with a fluid boundary layer. The transpiration cooling is a concept that combines the advantage of the internal cooling due to the presence of microchannels and film cooling, by leading the channels to the surface to be protected. The integration of a wall composed of a very large number of small pores allows to maximize the heat exchange area and to amplify the level of turbulence of the flow by the effect of pore tortuosity. Thus, for a given airflow, cooling is favored over the multi-perforation solution usually performed. Up to now unthinkable from an industrial point of view because of the complexity of manufacturing, parts of complex geometry including internal channels can now be made thanks to the emerging technologies of additive manufacturing.
Aim and description of the job:
This project focuses on the study of the concept of transpiration cooling through architectured metallic materials. The objective is to evaluate and optimize the efficiency of different model architectures using experimental testing, development and validation of models. This approach will determine the weight of each architectural parameter (porosity, tortuosity, connectivity, pore size...) on the transpiration cooling. The different model architectures will be studied and compared: walls with random porosity, with inclined microchannel, or assemblies of different stacks.
The work in this project will concern two PhD thesis, one performed at ONERA, the other performed at Grenoble (SIMAP laboratory) and will focus on two main parts:
- experimental part: different architectures will be fabricated, including the technique of additive manufacturing (by Electron Beam Melting, using the machine at Grenoble). The different materials will be characterized, in particular by X-ray tomography (in Grenoble) in order to obtain information about interconnectivity of the porosity, pore size, roughness of internal interfaces ... These structural analyses will be complemented by measures of gas permeability, thermal conductivity, acoustic absorption (these properties characterization will be performed at ONERA).
- modelling part: the final aim is to describe the flow through the porous material, taking into account the particular network topology and the impact of the internal flow on the thermal behavior of the material. The modeling work led at SIMAP concerns the determination of effective properties such as permeability, thermal conductivity, effective stiffness, in order to optimize the internal architecture of the material in respect of the set of requirements. ONERA will develop, in turn, for the transpirant walls, a full aero-thermal model incorporating these effective properties in order to get a boundary condition of type "limit layer law" to ensure proper development of the parietal layers, during the implementation of numerical simulations of reactive flow in the combustion chamber.
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Date of update May 29, 2013