Aeropropulsion and Power Technology

In phase I of this SBIR project we proposed the development of passive radiators to be used for adding low-frequency (<1000 Hz) acoustic damping, to mitigate combustion instability (screech), to augmentors. These radiators can be viewed as tuned acoustic absorbers and will be tuned to the resonant frequency(ies) of the sympathetic mode(s). Once tuned, they will provide highly effective fluid loading at their resonant frequencies tuned to offending modes, adding targeted acoustic damping to an augmentor. In addition to being very effective band-reject acoustic filters, at their resonant frequencies, radiators are effective high-pass acoustic filters (possessing broadband absorption capability) at frequencies above their tuned frequency. Passive radiators share this frequency-dependant characteristic of ‘ineffective at frequencies lower than tuned frequency, highly effective at tuned frequency, and effective at frequencies above tuned frequency’ with Helmholtz resonators (building block of acoustic liners). We also proposed to develop a software tool that assists the designers in the synthesis and analysis of stability mitigation solutions for augmentors. The model has been developed for one dimensional combustion rigs with no significant mean flow velocity. The extension of the thermoacoustics modeling tool to rigs with sizeable mean flow will be pursued in phase II of the project.