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TECHNICAL PAPERS

Large-Eddy Simulation of Transition in a Separation Bubble

[+] Author and Article Information
Stephen K. Roberts, Metin I. Yaras

Department of Mechanical and Aerospace Engineering, Carleton University, 3135 Mackenzie Bldg., Ottawa, Ontario, Canada K1S 5B6

J. Fluids Eng 128(2), 232-238 (Aug 10, 2005) (7 pages) doi:10.1115/1.2170123 History: Received March 07, 2005; Revised August 10, 2005

In this paper, large-eddy simulation of the transition process in a separation bubble is compared to experimental results. The measurements and simulations are conducted under low freestream turbulence conditions over a flat plate with a streamwise pressure distribution typical of those encountered on the suction side of turbine airfoils. The computational grid is refined to the extent that the simulation qualifies as a “coarse” direct numerical simulation. The simulations are shown to accurately capture the transition process in the separated shear layer. The results of these simulations are used to gain further insight into the breakdown mechanisms in transitioning separation bubbles.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the wind tunnel test section

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Figure 2

Measured streamwise distribution of the acceleration parameter

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Figure 3

Schematic of the computational domain

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Figure 4

Time-averaged velocity field in the region of the separation bubble: (a) LES, (b) experimental results (contours show 5% increments of u′∕Uref)

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Figure 5

Power spectra of u′∕Uref at various locations in the separation bubble: (a) experimental results, (b) LES

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Figure 6

Growth rates of disturbances at the dominant frequency

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Figure 7

Streamwise velocity contours at midspan during one full cycle of the dominant frequency (the dashed line at t0+T∕2 represents the time-averaged dividing streamline)

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Figure 8

Magnified view of streamwise velocity contours at midspan and t=t0+3T∕4 showing local reattachment of the flow

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Figure 9

Instantaneous streamlines demonstrating shear layer wavering at the T-S wavelength (λf)

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Figure 10

Contours of spanwise vorticity at midspan during one full cycle of the dominant frequency (the dashed line at t0+T∕2 represents the time-averaged dividing streamline)

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Figure 11

Magnified view of spanwise vorticity at mid-span and t=t0 (the dashed vertical line represents the location of the x−z plane shown in Fig. 1)

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Figure 12

Spanwise vorticity at t=t0 and x−xs=81mm (the dashed vertical line represents the location of the x−y plane shown in Fig. 1)

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Figure 13

Schematic representation of the vortex shedding process superimposed on the time-averaged dividing streamline (a) present results; (b) Hatman and Wang (7,46) model

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