65th NIA CFD Seminar:
ADVANCES IN GLOBAL INSTABILITY COMPUTATIONS: FROM INCOMPRESSIBLE TO HYPERSONIC FLOWS
Pedro Paredes, Post-doc, NASA Langley
October 20, 2015, 11:00 am, NIA, Rm 137
Abstract: Hydrodynamic instability theory studies the behavior of unperturbed flow fields upon the introduction of small-amplitude perturbations in order to improve the understanding of the processes involved in the onset of unsteadiness and the transition of laminar flow to a turbulent regime. The present work constitutes a step forward in advancing the frontiers of knowledge of fluid flow instability from a physical point of view, as a consequence of having been successful in developing groundbreaking methodologies for the efficient and accurate simulation of the transition phenomena in complex realistic three-dimensional flows. These achievements have been possible due to the huge computational efficiency improvements of the newly developed instability code for solving the very large sparse matrices discretizing the 2D and 3D partial differential equations (PDEs) governing the linear global instability analysis theories. The code implements high-order stable finite difference schemes for spatial discretization, which allows the use of efficient sparse linear algebra techniques without sacrificing accuracy. This permits a drastic reduction of the computing hardware on which state-of-the-art global instability analysis are performed. Furthermore, the extensibility of the novel three-dimensional parabolized stability equations (PSE-3D) algorithm developed in the framework of the present work to also study nonlinear flow instability permits transition prediction in complex flows of industrial interest, thus extending the classic PSE concept which has been successfully employed in the same context to boundary-layer type of flows over the last three decades.
Typical examples of incompressible flows, the instability of which has been analyzed without the need to resort to the restrictive assumptions used in the past, range from isolated vortices, and systems thereof, in which axial homogeneity is relaxed to consider viscous diffusion, as well as turbulent swirling jets, the instability of which is exploited in order to improve flame-holding properties of combustors. The instability of the wake of an isolated roughness element in a supersonic and hypersonic boundary-layer has also been analyzed with respect to its instability: excellent agreement with direct numerical simulation results has been obtained in all cases. Finally, instability analysis of Mach number 7 flow around an elliptic cone modeling the HIFiRE-5 flight test vehicle has unraveled flow instabilities over the entire geometry, results comparing favorably with ground and flight test predictions.
Speaker Bio: Dr. Pedro Paredes is currently a Post-doctoral Fellow at NASA Langley Research Center. He received his Ph.D. in Aerospace Engineering from Technical University of Madrid in Mach 2014. His research interests include linear flow instability and control of complex flows and study of laminar-turbulent transition in compressible boundary layers.
Additional information, including the webcast link, can be found at the NIA CFD Seminar website, which is temporarily located at http://www.hiroakinishikawa.com/niacfds/index.html