Abstract

The loudest source of high-speed jet noise appears to be describable by unsteady wave packets that resemble instabilities. We seek to reduce their acoustic impact by developing a novel control strategy that uses global modes to model their dynamics and structural sensitivity of the linearized compressible Navier-Stokes operator to select potentially effective linear feedback control strategies. The method is demonstrated on an axisymmetric Mach 1.5 jet and on a turbulent Mach 0.9 jet, both fitted with a simple nozzle. Direct numerical simulations using this control show significant noise reduction that improves with increasing control effort. An analysis of the uncontrolled and controlled mean flows reveal fundamental changes in the flow at frequencies lower than those used by the control. The non-normality of the global modes is shown to enable this control to affect a broad range of frequencies. An analysis of the controlled jet indicates that the control preferentially redistributes the flow disturbances towards global modes that are confined to the jet, relative to the uncontrolled jet, leading to a reduced sound field. Mean flow alterations are minor near the nozzle and become apparent only farther downstream.

Bio

Daniel J. Bodony is the Blue Waters Associate Professor and Donald Biggar Willett Faculty Scholar in the Department of Aerospace Engineering at the University of Illinois. He received his Ph.D. in Aeronautics & Astronautics from Stanford University in 2005 and his BSAAE and MSAAE degrees from Purdue University in 1997 and 1999, respectively. After working at the NASA Ames/Stanford Center for Turbulence Research he joined the University of Illinois in late 2006 as an assistant professor. He received an NSF CAREER award in 2012 in fluid dynamics and is an associate fellow of the AIAA.

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