Design and Evaluation of a Zero Mass Flow Liner

In this study, the concept of a zero mass flow liner is evaluated. The concept enables impedance control by the induction of, acoustically actuated, periodic bias flow through the facing sheet of the liner. By means of the periodic bias flow, the impedance of the liner is adapted to different grazing flow conditions. The equivalent fluid impedance model for perforated plates is modified to account for the effects of periodic bias and grazing flow. A generally applicable optimization routine, using the impedance of the lined surface as a boundary condition in a numeric calculation, is implemented. Based on the results of the optimization, a zero mass flow liner is manufactured and evaluated experimentally. The damping characteristics are assessed in the form of dissipated energy along the lined surface. Prediction and measurements show reasonable agreement. The zero mass flow liner delivers broadband dissipation of high peak value over a range of grazing flow Mach numbers. Under grazing flow, the effect of periodic bias flow is reduced. For a ratio of grazing to bias flow velocities larger than five, no appreciable effect is found. This poses considerable energy requirements on the actuation source for the application in high-Mach-number flow regimes.