A new approach for a compressor casing design has been developed using new design possibilities offered by additive manufacturing technologies. Tip clearance behaviour is a serious problem in compressor design leading to increased aerodynamic losses and limiting the operating range of a compressor through a decrease in surge margin. Efforts are necessary to minimise the tip clearance in the load cycle of an engine.

The approach presented in this work uses auxetic structures in a double-walled compressor casing with the aim to force the radial expansion behaviour of the inner casing wall in order to adapt the casing to the rotor. The studies of the casing and the calculations of the transient rotor displacement are carried out by using coupled-temperature-displacement calculations using commercial FEM-tools.

Elements which influence the radial expansion of the casing are identified with the aim of generating a modular system for future compressor casing developments. So the casing elements are adaptable to the radial expansion of a certain rotor. An improved tip clearance behaviour in relevant operating points is achieved. In the latter part of the paper, practical design considerations are made as the auxetic structures are integrated into the CAD model of an existing compressor casing. Design challenges are also briefly discussed.

This paper presents a new potential application of additive manufacturing technologies in future aero engine design. The focus of this paper is on the practical implementation of the new design freedom using the example of a compressor casing. The advantages for the overall engine performance as well as identified problems are also discussed qualitatively.

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