Structural analysis of an auxetic casing structure incorporating tip blowing casing treatment modification

In axial compressor design for aero engines high system efficiency and operational stability are two main objectives. Both depend on clearance-induced losses. Previous investigations at the Institute have resulted in a passive clearance controlled compressor design using additively manufactured auxetic casing structures. The extension to an active clearance controlled device to keep an approximately constant tip gap ratio during the entire flight mission is currently investigated. Constructive on these deliverables, the implementation of tip blowing casing treatment modification in a double-walled compressor casing including an auxetic inner structure is covered in this work and studied for maximum load conditions by means of Finite Element Analysis. The idea to supplement the current auxetic casing construction with casing treatment modification emerges from the aspiration to generate further stability improvements in the high-pressure domain and the exploitation of the design freedom provided by additive manufacturing. Key issues addressed in this work by conducting parameter studies are casing treatment positioning and corresponding structural correlations depending on circumferential quantity. The evaluation section concentrates mainly on the calculated stress level associated with tip blowing casing treatments because this value is crucial for prospective fatigue predictions. In order to compare the results, the auxetic casing structure without casing treatment modification serves as reference. Promising solutions for local stress reductions are also proposed and discussed. From a structural mechanics perspective, the casing treatment modification generates very high and comparable notch stress levels at each position. Placing the casing treatments at the framework of the auxetic cells and splitting the inner casing ring results in tolerable stress levels.