SBIR-STTR Award

We propose the development of passive radiators to be used for adding low-frequency (<1000 Hz) acoustic damping, to mitigate combustion instability in augmentors. These radiators can be viewed as tuned absorbers and will be tuned to the resonant frequency(ies) of the sympathetic mode(s). Once tuned, they will provide an effective fluid loading at their tuned frequency, i.e., the resonant frequency of a sympathetic mode. The number and locations of these radiators are design variables and will be determined so that the radiators couple well with the target mode(s) of the augmentor and thus absorb its(their) energy. We also propose to develop a software tool that assists the designers in the synthesis and analysis of stability mitigation solutions for augmentors. This design tool will be developed in Matlab/Simlink environment and will be based on two sub-systems of acoustics and combustion dynamics feeding back into each other. The modal data used in constructing the acoustic dynamics of the combustion system will be generated in ANSYS finite element analysis environment and then exported to Matlab

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.

Keywords:
Passive Radiator, Acoustic Damping, Acoustic Liner, Acoustic Absorption, Augmentor, Through Flow, Screech Mitigation, Tuned Absorber