Active Control of Combustion Noise by a Twin Resonator Trim Adjustment System

ABSTRACT

Variable volume Helmholtz resonator systems offer an advantage for trim adjustment active control in liquid rocket engines due to the low bandwidth requirement on the actuator. In the present work, a trim adjustment active control system based on twin variable volume Helmholtz resonators is investigated experimentally in open loop on a dedicated test setup. It is found that the twin variable resonators can control combustion noise in open loop in a methane-air combustion chamber. The frequency at which acoustic absorption is optimum deviates significantly from the fundamental system frequency at some of the equivalence ratios studied. This happens when the correlation for impedance available in the published literature is used as such. In this work, the impedance characteristics were derived directly from the measurements. It is demonstrated from the impedance characteristics that the twin resonator system is able to achieve consistently better performance than a single resonator over a range of equivalence ratios. It is concluded that the twin resonator system concept stands validated in open loop for combustion noise. A practical scheme for implementing a twin resonator active control system in open loop is outlined. The results indicate that twin resonators should be further investigated for closed loop suppression of thermoacoustic instability.

KEYWORDS:

• Combustion noise
• open loop
• active control
• twin resonator

Acknowledgments

The assistance of S. Sukesh, P. Jayesh and M. Babu for carrying out the experiments is gratefully acknowledged.