A ray tracing approach to calculate acoustic shielding by the silent aircraft airframe
2006 (English)In: Collection of Technical Papers - 12th AIAA/CEAS Aeroacoustics Conference, 2006, 2799-2818 p.Conference paper (Refereed)
The Silent Aircraft is in the form of a flying wing with a large wing planform and a propulsion system that is embedded in the rear of the airframe with intakes on the upper surface of the wing. Thus a large part of the forward-propagating noise from the intake ducts is expected to be shielded from observers on the ground by the wing. Acoustic shielding effects can be calculated by solving an external acoustic scattering problem for a moving aircraft. In this paper, acoustic shielding effects of the Silent Aircraft airframe are quantified by a ray-tracing method. The dominant frequencies from the noise spectrum of the engines are sufficiently high for ray theory to yield accurate results. It is shown that for low-Mach number homentropic flows, a condition satisfied approximately by the Silent Aircraft during take-off and approach, the acoustic rays propagate in straight lines. Thus, from Fermat's principle it is clear that classical Geometrical Optics and Geometrical Theory of Diffraction solutions are applicable to this moving-body problem as well. The total amount of acoustic shielding at an observer located in the shadow region is calculated by adding the contributions from all the diffracted rays (edge-diffracted and creeping rays) and then subtracting the result from the incident field without the airframe. Experiments on a model-scale geometry have been conducted in an anechoic chamber to test the applicability of the ray-tracing technique. The three-dimensional ray-tracing solver is validated by comparing the numerical solution with analytical high-frequency asymptotic solutions for canonical shapes.
Place, publisher, year, edition, pages
2006. 2799-2818 p.
Acoustic shielding, Acoustic shielding effects, Noise propagation, Silent aircraft airframe, Acoustic wave propagation, Aircraft propulsion, Airframes, Embedded systems, Numerical methods, Ray tracing, Wings, Noise abatement
Fluid Mechanics and Acoustics
IdentifiersURN: urn:nbn:se:kth:diva-155826ScopusID: 2-s2.0-33845667441ISBN: 1563478099ISBN: 9781563478093OAI: oai:DiVA.org:kth-155826DiVA: diva2:769063
12th AIAA/CEAS Aeroacoustics Conference, 8 May 2006 through 10 May 2006, Cambridge, MA
QC 201412052014-12-052014-11-132014-12-05Bibliographically approved