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The structure of two-dimensional separation

Published online by Cambridge University Press:  26 April 2006

Laura L. Pauley ,
Parviz Moin  and
William C. Reynolds
Laura L. Pauley
Affiliation:
The Pennsylvania State University, University Park, PA 16802, USA
Parviz Moin
Affiliation:
Stanford University, Stanford, CA 94305, USA and NASA/Ames Research Center, Moffett Field, CA 94035, USA
William C. Reynolds
Affiliation:
Stanford University, Stanford, CA 94305, USA and NASA/Ames Research Center, Moffett Field, CA 94035, USA
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Abstract

The separation of a two-dimensional laminar boundary layer under the influence of a suddenly imposed external adverse pressure gradient was studied by time-accurate numerical solutions of the Navier–Stokes equations. It was found that a strong adverse pressure gradient created periodic vortex shedding from the separation. The general features of the time-averaged results were similar to experimental results for laminar separation bubbles. Comparisons were made with the ‘steady’ separation experiments of Gaster (1966). It was found that his ‘bursting’ occurs under the same conditions as our periodic shedding, suggesting that bursting is actually periodic shedding which has been time-averaged. The Strouhal number based on the shedding frequency, local free-stream velocity, and boundary-layer momentum thickness at separation was independent of the Reynolds number and the pressure gradient. A criterion for onset of shedding was established. The shedding frequency was the same as that predicted for the most amplified linear inviscid instability of the separated shear layer.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 220 , November 1990 , pp. 397 - 411
Copyright
© 1990 Cambridge University Press

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