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ISBN 9783843947930

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978-3-8439-4793-0, Reihe Ingenieurwissenschaften

Lukas Dürrwächter
Simulation of Installation Effects on Open-Rotor Acoustics with a Coupled Numerical Tool Chain

197 Seiten, Dissertation Universität Stuttgart (2021), Softcover, A5

Zusammenfassung / Abstract

Aeroacoustic installation effects of open-rotor aircraft engines are investigated with special focus on scattering of their tonal noise by the airframe. To enable high-fidelity simulations at all relevant frequencies, an existing computational tool chain is extended. The existing "conventional" approach is based on flow fields obtained by solving the unsteady Reynolds-averaged Navier-Stokes equations and a subsequent acoustic evaluation with the acoustic analogy of Ffowcs Williams and Hawkings (FWH). To account for scattering effects at reasonable computational cost, the tool chain is supplemented by a further coupling with a fast multipole boundary element method, which is henceforth referred to as "coupled" approach. The influence of a background mean flow can be taken into account by applying a Lorentz transform to the boundary element problem and using the Möhring analogy instead of the FWH formulation to obtain the acoustic field incident to the scattering surface. The coupled tool chain is validated experimentally with measurement data of the propeller of an unmanned aerial vehicle with noise shielding by a screen. Further numerical validation is carried out on the basis of a model contra-rotating open rotor (CROR). The conventional and the coupled approach yield similar results. It is also shown in this context that the coupled tool chain can be used as a diagnostic means to separate scattering effects from other acoustic installation effects. As a full-scale application case, the coupled approach is used to assess the impact of different aircraft tail configurations on the noise emissions of a tail-mounted CROR in takeoff conditions. Some properties of the coupled method compared with the conventional one are discussed based on an investigation of the airframe effects on the noise signature of an H145 helicopter. Due to its moderate computational cost, the coupled tool chain is useful not only for analyses, but is also suited for parametric optimizations.