A methodology to predict thermoacoustic stability in rocket engines is presented. It is based on a divide and conquer principle. The central elements, consisting of the combustion chamber and the nozzle are calculated together directly by a hybrid approach using an extended version of the DLR's acoustic solver PIANO. Beside these central elements, the different components affecting the overall thermoacoustic stability are simulated separately and their properties are lumped into an adequate mathematical description, which is then integrated into PIANO. Each component is analyzed and optimized in its individual environment to reduce the complexity of the interaction processes, which govern thermoacoustics. The challenging step however is the incorporation of all components into a complete stability analysis and thereby keep the computational cost within reasonable limits to make this approach attractive for industrial purposes. In this report the fundamental approach is explained as well as the different components are described by means of their relevance for thermoacoustics and used modelling approaches are shown. Finally the strengths of the approach are confronted with its disadvantages. Especially its realizability and future prospects are discussed.
The noise emission of rocket engine test facilities and their impact on the environment comes more and more into focus. The key drivers are the engine exhaust jet itself, and its interaction or even coupling with a subsequent guide tube. To increase understanding of the interaction, and in preparation of future test facility design, a cold gas subscale test campaign was conducted with a reference guide tube. It was found that the main influencing parameter is the distance between the nozzle exit and guide tube inlet. This article is published with the permission of the authors granted to 3AF - Association Aéronautique et Astronautique de France (www.3AF.fr) organizer of the Space Propulsion International
Conference.
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