Simulation of Laminar Separation Bubble Instabilities
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Direct numerical simulations of the three-dimensional (3-D) time-dependent incompressible Navier-Stokes equations are performed to investigate the growth and stability of separation bubbles, generated by suction of fluid through the upper boundary of the simulation. Temporal stability of a family of matching analytic profiles for steady laminar separation bubbles is investigated by solving the Orr-Sommerfeld equation. A wave packet analysis of the growing modes suggests that absolute instability can exist in the strong reverse flow region of a laminar separation bubble. A comparative study is made of three cases. In the first a high suction strength is used to generate a self-excited irregular vortex shedding. The second and third cases use a lower suction strength and compare two and three-dimensional forced bubbles. Small scale structures in the 3-D forced bubble were found to have little effect on the time-averaged bubble length.
KeywordsDirect Numerical Simulation Reverse Flow Separation Bubble Separate Shear Layer Absolute Instability
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- Bestek, H., Gruber, K. and Fasel, H., 1993: Self-excited unsteadiness of laminar separation bubbles caused by natural transition, Proceedings of RAeS Conference on ‘The prediction and exploitation of separated flow’, 14.1–14.16.Google Scholar
- Gaster, M., 1963: On stability of parallel flows and the behaviour of separation bubbles, PhD Dissertation, University of London.Google Scholar
- Horton, H.P., 1968: Laminar separation in two and three dimensional incompressible flow, PhD Dissertation, University of London.Google Scholar
- Kleiser, L. and Schumann, U., 1980: Treatment of incompressibility and boundary conditions in 3-D numerical spectral simulation of plane channel flows, Proc. 3rd GAMM Conf. on Numerical Methods in Fluid Mechanics (Ed. E. H. Hirschel), 165–173.Google Scholar
- Lin, J.C.M., and Pauley, L.L., 1993 a: Unsteady laminar separation on low-Reynolds number airfoils, AIAA paper 93-0209.Google Scholar
- Lin, J.C.M., and Pauley, L.L., 1993 b: Unsteady view of transitional separation bubbles, Separated flow symposium of the ASME Fluids Engineering Conference.Google Scholar
- Maucher, U., and Rist, U. and Wagner S., 1994: Direct numerical simulation of airfoil separation bubbles, ECCOMAS.Google Scholar
- Niew, T.R., 1993: The stability of the flow in a laminar separation bubble, PhD Dissertation, University of Cambridge.Google Scholar
- Sandham, N.D. and Howard, R.J.A., 1995: Statistics database from direct numerical simulation of fully-developed turbulent channel flow, Queen Mary and Westfield College, Department of Engineering, QMW-EP-1106.Google Scholar
- Wilson, P.G. and Pauley, L.L., 1995: Two-dimensional large eddy simulation of a transitional separation bubble, Symposium on separated and complex flows ASME/JSME Fluid Engineering Conference.Google Scholar