Predicting the Thermal Conductivity of AlSi/Polyester Abradable Coatings: Effects of the Numerical Method

Abstract

The final target of this study is to achieve a better understanding of the behavior of thermally sprayed abradable seals such as AlSi/polyester composites. These coatings are used as seals between the static and the rotating parts in aero-engines. The machinability of the composite coatings during the friction of the blades depends on their mechanical and thermal effective properties. In order to predict these properties from micrographs, numerical studies were performed with different software packages such as OOF developed by NIST and TS2C developed at the UTBM. In 2008, differences were reported concerning predictions of effective thermal conductivities obtained with the two codes. In this article, a particular attention was paid to the mathematical formulation of the problem. In particular, results obtained with a finite difference method using a cell-centered approach or a nodal formulation allow explaining the discrepancies previously noticed. A comparison of the predictions of the computed effective thermal conductivities is thus proposed. This study is part of the NEWAC project, funded by the European Commission within the 6th RTD Framework programm (FP6).

A Novel Image Segmentation Approach for Microstructure Modelling

“…They are typically used to maintain seals at the blade tips in gas turbine compressors and are the subject of several previous microstructure modelling studies [1][2][3][4][5]. Specifically these materials are a aluminium silicon polyester and an aluminium silicon hexagonal boron nitride (hBN) composite.…”

“…Pixels originally belonging to the dislocator phase are then removed from this set. This is described by Equation (2).…”

“…Figure 15A shows that the proposed segmentation technique is repeatable despite changes in brightness of the input image. The proposed method out performs the relevant alternative method proposed by Bolot et al [3] in this respect. Adequate repeatability is found with changes in contrast ( Figure 15B) although the range of results is slightly larger than those generated by the Bolot method.…”

“…Thermally sprayed materials have been the subject of numerous works focusing on methods for modelling based on images of their microstructures [1][2][3][4][5]. In general these studies aim to predict the bulk properties of the material to validate the modelling route before using the model to investigate underlying mechanics and directions for future materials or processing parameters.…”

“…There are several steps in this process which introduce error into the final model [2]. The imaging method and settings, image segmentation and processing method, mesh generation, model formulation, boundary conditions and domain size must all be carefully considered for a representative model.…”