A NOVEL PURE WIRE MESH LINEAR LINER FOR ACOUSTIC REDUCTIONS IN A BROAD MACH NUMBER RANGE

The Conventional Perforated Liner (CPL) is highly sensitive to grazing flow, limiting its noise reduction ability to a narrow range of Mach numbers (Ma). To achieve higher performances at varying Ma in a whole flight envelope of aeroengines, a novel Pure Wire Mesh Liner (PWML) is proposed herein, with a thin porous facesheet sintered from two types of wire meshes replacing the perforated plate and directly bonded to the cavity. A simplified noise-reduction case from the aft nacelle of aeroengines is abstracted to demonstrate the acoustic advantage of this liner. A corresponding finite element model is set up to search the optimal impedance for the maximum reduction at an objective combination of Ma and frequency, and three liners including a CPL, a PWML and a Wire Mesh Perforated Liner (WMPL) are designed and manufactured to realize this optimal point. Then, the impedance characteristics of the three liners especially the PWML are investigated experimentally on the Beihang Grazing Flow Duct setup. As expected, the impedance spectra of all the three liners intersect at the objective Ma. More importantly, due to a better acoustic linearity, the PWML exhibits a much lower sensitivity to the Mach number and aligns more closely with the optimal impedance trend. So, the transmission loss of the PWML evaluated using its educed impedance input into the simplified model achieves a significant promotion across the whole broad Mach number range from 0 to 0.5, largely superior to the other two.