Seminar: Controlling and Harnessing Flow-Acoustic Resonance in Impinging Jets -- A Case Study in Active Flow Control
The literature is replete with examples where flow-acoustic coupling leads to resonance and therefore an unsteady flowfield. Examples of resonance dominated flows in jets include: screech tones, conspicuously present in non-ideally expanded jets; edge tones generated due to the presence of an ‘edge’ in the jet hydrodynamic field and impinging tones which occur when a high-speed jet impinges on a surface such as those used in VTOL/STOVL aircraft during hover. Such flow-induced resonance is almost always undesirable since it leads to problems such as very high noise levels, sonic fatigue of nearby structures and other issues. In the case of impinging jets, this coupling also results in significant lift loss during hover. Our research group at the Florida Center for Advanced Aero-Propulsion - FCAAP (Tallahassee) has been exploring ways to better understand and more efficiently control such flows at high speeds, in particular supersonic impinging jets and supersonic flow over cavities. In this talk we review some representative experimental results in the context of “Aeroacoustics and Control of Supersonic Impinging Jets.” We will examine techniques that worked, somewhat worked and barely worked and explore why this is so. The need for unsteady actuators with high control authority and flexibility in terms of amplitude and frequency – the ‘ideal actuator’ is apparent in many AFC problems. An interesting outcome of this work was the idea for harnessing impinging jet aeroacoustics to develop Resonance Enhanced Microjet (REM) actuators. This design leverages similar flow-acoustic coupling - but at microscales, O (100µm), to produce a robust and fairly simply, high control authority actuator. Properties, physics and successful/unsuccessful uses of these actuators will also be discussed in this talk.
About the Speaker: Dr. Farrukh S. Alvi is the Associate Dean for Research and Graduate Studies and Don Fuqua Eminent Scholar and Professor of Mechanical Engineering at Florida State University. He has broad research interests, including active-adaptive flow control, aerodynamics and propulsion, microfluid dynamics and diagnostics. His research has encompassed shock boundary layer interactions, the aeroacoustics of high speed jets, including supersonic impinging jets, and the associated problems of compressible mixing and jet noise. Dr. Alvi has previously served as the founding director of the Florida Center for Advanced Aeropropulsion, a statewide partnership between universities and industry, that has been selected by the FAA as a national Center of Excellence. Dr. Alvi is an elected fellow of the American Society of Mechanical Engineers, has served on the editorial board of the AIAA Journal and holds a Ph.D. in mechanical engineering from Pennsylvania State University.