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Analysis of Fluid Motion in Dynamic Stall and Forced Cylinder Flow Using Koopman Operator Methods

[+] Author Affiliations
Bryan Glaz

U.S. Army Research Laboratory, Aberdeen Proving Ground, MD

Maria Fonoberova, Sophie Loire

Aimdyn, Inc., Santa Barbara, CA

Igor Mezić

University of California Santa Barbara, Santa Barbara, CA

Paper No. IMECE2014-39146, pp. V001T01A008; 18 pages
  • ASME 2014 International Mechanical Engineering Congress and Exposition
  • Volume 1: Advances in Aerospace Technology
  • Montreal, Quebec, Canada, November 14–20, 2014
  • Conference Sponsors: ASME
  • ISBN: 978-0-7918-4642-1
  • Copyright © 2014 by ASME


Potential analogs between dynamics induced by periodic passage through a bifurcation critical value and the nonlinear dynamics associated with the aerodynamic dynamic stall problem are presented for the first time. Koopman operator methods are used to study the spectral features of a streamwise oscillating cylinder which exhibits wake dynamics due to externally forced oscillations through a Hopf bifurcation critical value. Koopman decomposition results show that the system transitions to a more continuous spectrum compared to the discrete spectrum associated with a stationary cylinder in post-critical flow. Finally, Fourier analysis of flow variables associated with an oscillating airfoil under dynamic stall conditions were compared with the oscillating cylinder spectra. The spectral characteristics of the two systems exhibited similar frequency broadening behavior induced by the externally forced oscillations. Therefore, the results indicate that the nonlinear dynamics associated with dynamic stall appear to have strong linkages to a system oscillating through a bifurcation critical value.

Copyright © 2014 by ASME



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