Noise Generation Mechanisms in Imperfectly Expanded High-Speed Jets
Abstract
Although significant progress has been made in measuring and predicting noise from jets, a clearunderstanding of noise generation m""echanisms remains elusive. In particular, the kinematic andthermodynamic processes by which a relatively small fraction of the turb"ulent and thermal energyof the jet is converted into highly destructive acoustic energy is unclear. This is particularly true ofim"perfectly expanded jets of interest to the military and has inhibited the development of effectivecontrol techniques. In this work,"" we will examine imperfectly expanded jets, particularly in theoverexpanded condition. Our primary emphasis is on broadband shock a""ssociated noise (BBSAN)and turbulent mixing noise, with secondary emphasis on Mach wave steepening processes andscreech. We use a"" holistic approach comprised of two thrusts. In the first, we seek specifically tounderstand how energy is transferred from the dom"inant hydrodynamic (and thermal) modes intothe acoustic mode. The second endeavor will adopt a dynamical systems perspective to determinehow turbulent fluctuations from different regions of the jet are filtered by the surrounding unsteadyflow to yield the observed phenomena. Particular stress is placed on directivity and intermittencyand their difference from the perfectly expanded condition. Conceptual studies will use the understandingderived from the two thrusts to examine the implications of preferential heating g"radientsin the nozzle exit plane and small-perturbation pulsing, respectively, for control. The analysis willbe based on Large-Edd""y Simulations of jets at imperfectly expanded conditions for which validationdata is available. For the energy focus, we will use D""oak~s decomposition to separate thefluid-thermodynamic (hydrodynamic, acoustic and thermal) modes in a time-accurate fashion. Thei"nter-modal energy transfer associated with the quasi-periodic shock cell and feedback loops willbe assessed with the total fluctuating enthalpy (TFE) equation to unmask acoustic energy dynamics.The results will then be employed to develop a simplified propagator model for imperfectlyexpanded jet noise. The dynamical systems perspective will be accomplished by suitably forcingdifferent regions of the evolving turbulent jets with the synchronized LES technique. The filteringproperties of the jet will then be extracted t"o determine how local fluctuations are transformedinto BBSAN, turbulent mixing noise, screech and Mach wave steepening. By subjecti""ng actuatorbasedperturbations to energy decomposition, we expect to determine precisely how these affectthe acoustic mode. The res"ults will provide unparalleled insights into the dynamics of imperfectlyexpanded jets. In addition to a clearer understanding of ac"oustic energy dynamics, the results willaid in the development of control techniques by educing the receptivity of the acoustic mod"e todifferent perturbations.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2017
- Source ID
- N000141712584
Entities
People
- Datta V. Gaitonde
Organizations
- Office of Naval Research
- Ohio State University
- United States Navy