Experimental verification of a finite length tuning concept for acoustic lining design

Abstract A joint program between the Boeing Commercial Airplane Company and the United Kingdom National Gas Turbine Establishment was carried out to experimentally verify an acoustic finite length tuning concept for low frequency lining designs. By properly accounting for the reflective properties of discontinuous admittance via mode matching techniques, five panels were designed to demonstrate the length tuning concept. Three panels were designed for no flow and two panels were designed for a flow Mach number of 0.2. The panels were of conventional design with perforated face sheets and rectangular cavity resonators. The test results confirmed the theoretical predictions that an optimum finite length lining of given impedance will produce a maximum insertion loss greater than a longer length lining of equal impedance.