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BTU
Acoustic and aerodynamic design and characterization of a small-scale aeroacoustic wind tunnel
(2009)
Akustische Polaren
(2010)
Der leise Flug der Eulen
(2011)
Integrierte aerodynamische und akustische Auslegung eines Propellers für Ultraleichtflugzeuge
(2011)
Three-Dimensional Acoustic Source Mapping with Different Beamforming Steering Vector Formulations
(2012)
Application of Beamforming and Deconvolution Techniques to Aeroacoustic Sources at Highspeed Trains
(2012)
The use of porous materials is one of several approaches to passively control or minimize the generation of flow noise. In order to investigate the possible reduction of noise from struts and other protruding parts (for example components of the landing gear or pantographs), acoustic measurements were taken in a small aeroacoustic wind tunnel on a set of circular cylinders with a soft porous cover. The aim of this study was to identify those materials that result in the best noise reduction, which refers to both tonal noise and broadband noise. The porous covers were characterized by their air flow resistivity, a parameter describing the permeability of an open-porous material. The results show that materials with low air flow resistivities lead to a noticeable flow noise reduction. Thereby, the main effect of the porous cylinder covers is that the spectral peak of the aeolian tone due to vortex shedding appears much narrower, but is not suppressed completely. Based on the measurement results, a basic model for the estimation of the total peak level of the aeolian tone was derived. In addition to the minimization of the vortex shedding noise, a reduction of broadband noise can be observed, especially at higher Reynolds numbers. The noise reduction increases with decreasing air flow resistivity of the porous covers, which means that materials that are highly permeable to air result in the best noise reduction.
We present a strategy for the recovery of a sparse solution of a common problem in acoustic engineering, which is the reconstruction of sound source levels and locations applying microphone array measurements. The considered task bears similarities to the basis pursuit formalism but also relies on additional model assumptions that are challenging from a mathematical point of view. Our approach reformulates the original task as a convex optimisation model. The sought solution shall be a matrix with a certain desired structure. We enforce this structure through additional constraints. By combining popular splitting algorithms and matrix differential theory in a novel framework we obtain a numerically efficient strategy. Besides a thorough theoretical consideration we also provide an experimental setup that certifies the usability of our strategy. Finally, we also address practical issues, such as the handling of inaccuracies in the measurement and corruption of the given data. We provide a post processing step that is capable of yielding an almost perfect solution in such circumstances.
An efficiency improvement for the implementation of a semi-analytical model of plate silencers in ducts is presented in this work. It is shown that a high approximation quality can be maintained even if the computation effort is reduced significantly. Thus, preliminary designs of plate silencers for specific purposes can be conducted with little effort. In addition, the accelerated implementation is utilized to perform an extensive parameter variation in order to find a best case configuration of silen properties and corresponding design rules. The results of these studies show that a tuning of plate and geometry parameters allow for substantial increases in a silencer's attenuation performance.