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A theoretical study of the acoustic impedance of orifices in the presence of a steady grazing flowAn analysis of the oscillatory fluid flow in the vicinity of a circular orifice with a steady grazing flow is presented. The study is similar to that of Hersh and Rogers but with the addition of the grazing flow. Starting from the momentum and continuity equations, a considerably simplified system of partial differential equations is developed with the assumption that the flow can be described by an oscillatory motion superimposed upon the known steady flow. The equations are seen to be linear in the region where the grazing flow effects are dominant, and a solution and the resulting orifice impedance are presented for this region. The nonlinearity appears to be unimportant for the usual conditions found in aircraft noise suppressors. Some preliminary conclusions of the study are that orifice resistance is directly proportional to grazing flow velocity (known previously from experimental data) and that the orifice inductive (mass reactance) end correction is not a function of grazing flow. This latter conclusion is contrary to the widely held notion that grazing flow removes the effect of the orifice inductive end correction. This conclusion also implies that the experimentally observed total inductance reduction with grazing flow might be in the flow within the orifice rather than in the end correction.
Document ID
Document Type
Conference Paper
Rice, E. J.
(NASA Lewis Research Center Cleveland, OH, United States)
Date Acquired
September 3, 2013
Publication Date
January 1, 1976
Subject Category
Fluid Mechanics And Heat Transfer
Report/Patent Number
Meeting Information
Meeting: Meeting of the Acoustical Soc. of Am.
Location: Washington, DC
Country: United States
Start Date: April 5, 1976
End Date: April 9, 1976
Accession Number
Distribution Limits
Work of the US Gov. Public Use Permitted.
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