Acoustic wall treatments are investigated and improved for the application in aero-engines and stationary gas turbines. These so called liners are available in many different configurations for very different applications. Our work is focused on the investigation of perforated liners and Helmholtz resonator liners.
Perforated Liners are used in combustion chambers of aero-engines and stationary gas turbines for the reduction of thermo-acoustic instabilities. This ensures the stable operation of the combustor and allows the implementation of modern, low-emission combustion concepts. Figure 1 shows a generic design of such a liner. It consists of a perforated material, here it is a cylindrical tube with a defined hole pattern. A bias flow through the perforation can significantly increase the acoustic absorption. It is generally assumed that this benefit in damping results from an interaction between the acoustical waves and aerodynamic vorticity structures. However, the detailed knowledge of the physical mechanisms is still insufficient. Our goal is to get a better physical understanding of this process and optimize the liners for practical application. Perforated liner Helmholtz Resonator Liners are used in the inlet and bypass-duct of aero-engines. They attenuate the propagation of mainly tonal frequency components, e.g. the blade-passing-frequency of the fan, and therefore reduce the radiated sound power significantly. Figure 2 shows a basic design of a Helmholtz resonator panel consisting of a perforated face sheet, a solid backing plate, and a honeycomb structure in-between, resulting in an array of Helmholtz resonators. The Helmholtz resonator is a spring-mass system with the air volume inside the cavity being the spring and the air in the hole being the mass. Incident sound waves excite an oscillation of this system. The acoustic energy of the incident sound is transformed into heat due to friction losses, compression and expansion losses in the cell and vorticity shedding. In operation these liners are exposed to high grazing flow velocities and high sound amplitudes. The influence of these parameters on the damping performance is of special interest. Helmoltz resonator liner . Aero-engine inlet with Helmholtz resonator liner
Perforated Liners are used in combustion chambers of aero-engines and stationary gas turbines for the reduction of thermo-acoustic instabilities. This ensures the stable operation of the combustor and allows the implementation of modern, low-emission combustion concepts. Figure 1 shows a generic design of such a liner. It consists of a perforated material, here it is a cylindrical tube with a defined hole pattern. A bias flow through the perforation can significantly increase the acoustic absorption. It is generally assumed that this benefit in damping results from an interaction between the acoustical waves and aerodynamic vorticity structures. However, the detailed knowledge of the physical mechanisms is still insufficient. Our goal is to get a better physical understanding of this process and optimize the liners for practical application.
Helmholtz Resonator Liners are used in the inlet and bypass-duct of aero-engines. They attenuate the propagation of mainly tonal frequency components, e.g. the blade-passing-frequency of the fan, and therefore reduce the radiated sound power significantly. Figure 2 shows a basic design of a Helmholtz resonator panel consisting of a perforated face sheet, a solid backing plate, and a honeycomb structure in-between, resulting in an array of Helmholtz resonators. The Helmholtz resonator is a spring-mass system with the air volume inside the cavity being the spring and the air in the hole being the mass. Incident sound waves excite an oscillation of this system. The acoustic energy of the incident sound is transformed into heat due to friction losses, compression and expansion losses in the cell and vorticity shedding. In operation these liners are exposed to high grazing flow velocities and high sound amplitudes. The influence of these parameters on the damping performance is of special interest.
The acoustic properties of the liners are determined in a flow tube optimized for acoustical measurements (LINK). With parametric studies the influence of acoustic, aerodynamic, and geometric parameters can be identified with a high accuracy. This work is integrated in several projects and we cooperate closely with national and international partners from academia and industry.
In 2011, the hot-acoustic-testrig (HAT) started operation. With this unique facility we are able to investigate the damping characteristics of liners also under the influence of elevated pressure and temperature.