Active-adaptive Control of Acoustic Resonances in Flows
Several fluid flow problems related to propulsion and power generation exhibit strong acoustic resonances. Produced due to interactions of the acoustics with other underlying unsteady mechanisms such as unsteady heat-release or shear flow instability, these resonances manifest as large and sustained pressure oscillations. In addition to the obvious undesirable effect of high ambient noise and acoustic fatigue, these oscillations are coupled with other damaging effects such as excessive vibrations, high bum rates, lift-loss, and ground erosion. Compromises made in order to reduce these oscillations lead to departures from the desired operating conditions and can in turn result in suboptimal perfonnance with reduced heat-output, increased emissions, or decreased efficiency. Over the past few years, active control technology has been increasingly sought after to realize the desired performance metrics in these problems without encountering resonant behavior. In order to provide guaranteed and unifonn performance over a large range of operating conditions in the presence of various system uncertainties, it has been demonstrated in these problems that a model-based approach to designing the control strategy is feasible and scalable, and leads to a reliable and improved pressure reduction at the desired operating conditions. In this chapter, two examples of such fluid flow problems, combustion-instability and impingement-tones in supersonic flows, and their active control will be discussed. Models of the resonant mechanisms using both physically-based and system-identification principles are presented. In active-adaptive control of combustion systcms, Posi-cast control methods and their closed-loop performance in practical combustors are discussed. In active-adaptive control of supersonic impingement tones, a POD-based active control strategy and the corresponding experimental results from a Short Takeoff Vertical Landing (STOVL) supersonic jet facility at Mach 1.5 are presented.
KeywordsAcoustic Resonance Resonant Mechanism Fluid Flow Problem Combustion Dynamic Delay Controller
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