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Aeroacoustic tunnel effect in noise shielding problems

Delfs, Jan / W. (2014) Aeroacoustic tunnel effect in noise shielding problems. In: AIAA/CEAS 20th Aeroacoustics Conference. AIAA. 20th AIAA/CEAS Aeroacoustics Conference 2014 (part of Aviation 2014), 16.-20. Juni 2014, Altanta, USA. doi: 10.2514/6.2014-3181.

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Official URL: http://arc.aiaa.org/doi/abs/10.2514/6.2014-3181


The question is addressed, under which conditions the commonly applied neglect of shear in the flow past an acoustically shielding object may not be justified, even at low Mach numbers, representative for take-off and landing of aircraft. The numerical results generated to quantify the engine noise shielding effect of a high lift airfoil in the EU project NACRE are taken as starting point. These results showed an unexpectedly significant influence of shear on the shielding when compared to a simplified approach neglecting the shear at a low Mach number of M = 0.3. The paper gives an explanation of this phenomenon based on total reflection and accompanying evanescent waves in the shear flow near the gap slot. The problem is stripped down to the essential physical ingredients and is then reproduced in a much more simplified setup. The investigation shows that evanescent waves below a reflecting shear layer may become propagational in the presence of an edge or slot, i.e. sound may "tunnel" through even a totally reflecting shearlayer and radiate into the acoustic shadow zones predicted with simple methods, which neglect shear.

Item URL in elib:https://elib.dlr.de/93133/
Document Type:Conference or Workshop Item (Speech)
Title:Aeroacoustic tunnel effect in noise shielding problems
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Journal or Publication Title:AIAA/CEAS 20th Aeroacoustics Conference
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:Aeroacoustic shielding, acoustic refraction, evanescent waves, acoustic tunnel effect
Event Title:20th AIAA/CEAS Aeroacoustics Conference 2014 (part of Aviation 2014)
Event Location:Altanta, USA
Event Type:international Conference
Event Dates:16.-20. Juni 2014
Organizer:American Institute of Aeronautics and Astronautics (AIAA)
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Flight Physics (old), L - Simulation and Validation (old)
Location: Braunschweig
Institutes and Institutions:Institute of Aerodynamics and Flow Technology > Technical Acoustics
Deposited By: Delfs, Prof.Dr. Jan Werner
Deposited On:05 Dec 2014 11:18
Last Modified:31 Jul 2019 19:50

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