Acoustic Black Hole Damper for Thermoacoustic Instability Control in a Hydrogen Combustor

Abstract

Thermoacoustic instabilities remain a major challenge in the operation and development of modern gas turbine combustors for power generation and propulsion. In laboratory environments, such instabilities can also hinder the accurate characterization of key thermoacoustic properties of the flames. Many modern combustors therefore employ wall-mounted acoustic dampers, such as Helmholtz or quarter-wave resonators; however, these devices are typically effective only over narrow frequency ranges. In this study, the application of perforated acoustic black holes (ABHs) as broadband passive dampers for thermoacoustic instability mitigation is investigated. Several ABH designs are additively manufactured and experimentally characterized through scattering matrix measurements. A reduced-order model based on the transfer matrix method is developed and is shown to be in good agreement with the experimental results. Using this validated model, a damper design is optimized to maximize acoustic dissipation over the frequency range 500-2000 Hz. The optimized perforated ABH damper is installed in the plenum section of the combustor test rig, and its thermoacoustic performance is evaluated over a range of equivalence ratios and outlet boundary conditions. Across all operating conditions considered, the ABH damper leads to a substantial reduction of the amplitude of the acoustic pressure oscillations. These results demonstrate the potential of perforated ABH-based dampers as a robust and broadband passive solution for mitigating thermoacoustic instabilities in hydrogen-fueled combustors.

Figures (17)

• Figure 1: Sketch of the perforated ABH damper including its relevant geometrical parameters (left) and its simplified model for the transfer matrix method (right).
• Figure 2: a) Non-reactive test rig. b) Perforated ABH damper mounted on the cage module of the combustor setup. The damper is aligned such that the cavity height increases from left to right.
• Figure 3: Lab-scale atmospheric low Mach number combustor equipped with microphones and perforated ABH damper. Mic: microphones, ABH: Acoustic black hole, C.C: combustion chamber. For the baseline configuration, the ABH blocks are replaced with glass windows.
• Figure 4: C1 (left) and C2 (right) damper design. The perforated plate is printed separately and glued on to the bottom surface of the ABH block. Dimensions in mm.
• Figure 5: Measured a) scattering matrix, b) dissipation coefficients of C1 and C2 designs. $\alpha_u:$ upstream dissipation, $\alpha_d:$ downstream dissipation.