科研之友
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摘要
Liners backed by a resonant cavity and traversed by a bias flow are widely used for acoustic damping in aeronautical engines. Their design relies on a relatively complex optimization procedure with a large number of parameters to examine. It is shown in this study how to reduce this number by maximizing absorption in two limit regimes where the choice of the optimal bias flow velocity and size of the back cavity can be decoupled. These developments apply for perforated plates of different porosity and thickness in the absence of grazing flow. In these regimes, the optimal bias flow velocity is only controlled by the plate porosity while the size of the back cavity fixes the peak absorption frequency. The first absorption regime reached at high Strouhal numbers is characterized by a Helmholtz resonance (He << 1) and a narrow frequency absorption bandwidth. The Mach number associated to the optimal bias flow velocity is then given by M-c = (2/pi)sigma, where a is the plate porosity. This regime minimizes the size of the resonant back cavity, but the absorption bandwidth narrows also with the Strouhal number. The second absorption regime reached at low Strouhal numbers operates with a quarter-wave resonator (He similar or equal to pi/2) and a bias flow velocity fixed by M-c = sigma/2. This regime offers a wide absorption bandwidth around the peak absorption frequency well suited for low frequency dampers when the bias flow velocity may vary within the system. Theoretical expressions derived in this study are validated against experimental data in the two regimes identified. They may be used to ease the design of robust dampers to hinder self-sustained thermo-acoustic instabilities when the instability frequency varies.
- 出版日期2013-1
