Sound within aircraft engines can be 120–160 dB, pushing the validity of linearized governing equations. Moreover, some components of sound within a viscothermal mean flow boundary layer over an acoustic lining may be amplified by a factor of () in a typical aircraft engine compared with the sound outside the boundary layer, which may be expected to trigger nonlinear effects within the boundary layer. This is in addition to the well-known nonlinear effects within the holes of the perforated lining facing sheet. This paper presents a mathematical investigation into the effects of weak nonlinearity on the acoustics within a thin parallel mean flow boundary layer in flow over an acoustic lining in a cylindrical duct. (This is the first investigation of nonlinear acoustics in a boundary-layer flow over a nonrigid surface, to our knowledge.) In certain cases, a surprisingly large acoustic streaming effect is found that escapes the mean flow boundary layer and pervades well out into the interior of the duct.
Nonlinear Acoustics in a Viscothermal Boundary Layer over an Acoustic Lining
AIAA Journal ; 58 , 2 ; 673-686
2019-10-21
14 pages
Article (Journal)
Electronic Resource
English
Acoustics in a Two-Deck Viscothermal Boundary Layer over an Impedance Surface
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