Orifice Impedance under Grazing Flow: Modal Expansion Approach

G. Kooijman, Y. Aurégan, A. Hirschberg
2005 11th AIAA/CEAS Aeroacoustics Conference   unpublished
Acoustic lining is used in jet engines to reduce noise radiation. The liners consist of up to several layers of perforated plate backed with honeycomb structure. A key aspect in their performance is the influence of the grazing flow on the perforates' impedance. In our research we concentrate on the effect of flow on a single orifice. Comparison of previous experiments with existing theory was unsatisfactory. Especially we concluded that the boundary layer thickness of the grazing flow is an
more » ... azing flow is an important factor. In this paper we present a theoretical model, which accounts for boundary layer characteristics. Two parallel 2D ducts with partially an interconnection, representing the orifice domain, are considered. The eigen modes in the ducts and orifice domain are solved numerically for any given flow profile. By subsequent matching of the modal expansions of the acoustical field between the domains, the acoustic impedance of the orifice is determined. Comparison with impedance tube measurements shows reasonably good agreement for both resistance and end correction. However, numerical convergence of the model is not yet established.
doi:10.2514/6.2005-2857 fatcat:dibn3rhvxfd23olar5iahpuism