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AEM Seminar: Perturbation analysis of Three-Dimensional Steady and Unsteady Flow Fields

Dr. Datta V. Gaitonde, John Glenn Chair, Ohio Research Scholar, Mechanical & Aerospace Engineering, Ohio State University

2:30 PM on 2018-03-02

Akerman 319


High-fidelity simulations, such as those using Direct Numerical Simulations and Large-Eddy Simulations, have become increasingly commonplace. Such databases capture the pertinent spatio-temporal scales of interest to the aerospace engineer, but yield a large amount of data. While statistical analyses provide insight into some of the more important dynamics, insight into the sensitivity and underlying stability mechanisms could greatly aid in the development of flow control techniques. In this talk, we will discuss the use of two distinct approaches, Synchronized Large Eddy Simulation (SLES) and Mean Flow Perturbation, that promise to provide such insight by examining perturbation propagation in steady and unsteady flowfields. The appropriate equations are the linearized Navier–Stokes equations, except that when the flow under consideration is itself unsteady, the linearization must be performed about the instantaneous evolving state, which informs the unsteady coefficients of the linearized equations. To avoid forming the Jacobians, the SLES method uses a pair (denoted “baseline” and “twin”) of simultaneous synchronized LES. At each time-step, small disturbances whose propagation characteristics are to be studied, are introduced into the twin through a forcing term. The form of the forcing can be arbitrary (white noise for example) or “native” i.e., related to local turbulent fluctuations. The linearized response of turbulent state can be extracted by suitably post-processing the solutions. The rationale for procedures required to ensure the success of the method, designated anchoring and constraining, will be discussed. The former ensures that the two chaotic systems do not drift away from each other, allowing for a time-local analysis of perturbation evolution. The latter becomes essential when absolute instabilities are present, and serves to limit the most amplified mode. The application of the technique to jet noise source localization and shock/turbulent interactions has revealed crucial insights into the nature of sound production by turbulence, as well as the signatures of absolute instabilities in closed versus open separated flows. For steady basic states, the talk will explore a technique to obtain global modes of complex flowfields by examining the growth of volume-based random perturbations over short time durations.

Bio:

Dr. Datta V. Gaitonde is the John Glenn Chair and Ohio Research Scholar in the Mechanical and Aerospace Engineering Department. He has diverse research interests, including shock/turbulent interactions, jet noise, hypersonic transition, flow control, bluff body flows, scramjet flowpaths and algorithm development. He has over 200 publications in journals, conferences and books and has delivered numerous national and international presentations. He has served on various advisory panels for national agencies and is a Deputy Editor of the AIAA Journal. He is a recipient of several awards and is a Fellow of the Air Force Research Laboratory, ASME and AIAA.


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