Abstract
A separated boundary layer flow at the rear of a bump is considered and two-dimensional flow states at increasing Reynolds numbers are computed using a nonlinear continuation procedure for the stationary Navier–Stokes system. The global instability analysis of the steady states is performed by computing two-dimensional temporal modes. The analysis reveals non-normal modes which are able to describe localized initial perturbations associated with large transient energy growth. At larger time a global low-frequency oscillation is found accompanied with periodic regeneration of the flow perturbation inside the bubble, as the consequence of non-normal cancellation of modes. The initial condition provided by the optimal perturbation analysis is applied to Navier–Stokes time integration and is shown to trigger nonlinear ‘flapping’ typical for separation bubbles.
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Acknowledgments
Parts of the computations have been performed on the NEC-SX8 of the IDRIS, France. The authors would like to thank Matthieu Marquillie for providing the DNS code.
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Ehrenstein, U., Gallaire, F. (2009). Global Low-Frequency Oscillations in a Separating Boundary-Layer Flow. In: Braza, M., Hourigan, K. (eds) IUTAM Symposium on Unsteady Separated Flows and their Control. IUTAM Bookseries, vol 14. Springer, Dordrecht. https://doi.org/10.1007/978-1-4020-9898-7_10
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DOI: https://doi.org/10.1007/978-1-4020-9898-7_10
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