Large-Scale Unsteadiness in Compressible, Turbulent Flow

Large-scale unsteadiness lies at the heart of many of the design challenges associated with flight at high Mach numbers. Phenomena such as sound generation, fatigue loading, mixing, and separation are driven by turbulent motion on scales larger than the boundary layer thickness and longer than the boundary layer time scale /Ue,. This talk will focus on large-scale unsteadiness in attached and separated turbulent boundary layer flows in the supersonic regime. High-fidelity, implicit large-eddy simulations of a supersonic turbulent boundary layer flow were carried out using different numerical algorithms and codes. In the region where the boundary layer was well developed, agreement was obtained between results obtained with different numerical approaches and experimental turbulent boundary layer profiles. Correlations characterizing large-scale structures in the flow turbulence were also explored. It was found that useful comparison between computation and experiment demanded detailed understanding of the experimental techniques, and a careful replication of those methods was required in reducing the computational data. With this approach, many of the features of the large-scale structures observed in computation and experiment matched. For separated, compressible, turbulent boundary layer flows, spectra of wall pressure fluctuations caused by separation shock unsteadiness were compared using data obtained from wind tunnel experiments, the HIFiRE-1 flight test, and large-eddy simulations. The results were found to be in generally good agreement, despite differences in Mach number and two orders of magnitude difference in Reynolds number. Relatively good agreement was obtained between these spectra and the predictions of a theory developed by Plotkin. The predictions of this theory are also qualitatively consistent with the results of experiments in which the shock motion was synchronized to controlled perturbations. The results support the idea that separation unsteadiness has common features across a broad range of compressible flows, and that it behaves as a selective amplifier of large-scale disturbances in the incoming flow. BIO Jonathan Poggie is a researcher in the fields of fluid mechanics and plasmadynamics. He has worked at the Air Force Research Laboratory since earning his Ph.D. from Princeton University in 1995. He is an experienced technical team leader and program manager, focusing on technology to enable flight at extremely high speed (supersonic and hypersonic aircraft). He has unusually broad research experience, with publications in the experimental, computational, and theoretical sides of high-speed flow. As an educator, he has served as a research adviser to several graduate students, and has taught at the graduate level. Refreshments will be served at 3:45 p.m. Photo