Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Large-Eddy Simulation of the Vortical Motion Resulting from Flow over Bluff Bodies
Large-Eddy Simulation of the Vortical Motion Resulting from Flow over Bluff Bodies
Pages 580-591
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From page 580... ...
The time-averaged Reynolds stress results of the formation region reveal symmetric characteristics similar to published experunental data at the sub-critical Reynolds number of 140,000. The LES results of the hydrofoil showed laminar separation of Me upstream upper boundary layer followed by transition to turbulence and reattachment near the beginning of Me trailing INTRODUCTION Many engineering problems within Me Navy involve very complicate flow behaviors that cannot be accurately simulated using simple computational mesons.
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From page 581... ...
At the latter Re in particular, they showed the spectral amplitudes to vary significantly across the shear layer at the predominant frequencies of the small-scale instabilities as well as the frequencies of the much larger scale Strouhal vortex. Through flow visualization testing, Wei and Smith proposed a different phenomena for the separated shear layer physics.
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From page 582... ...
In the following work, results from largeeddy simulations will be presented at a Reynolds number of 8000 to investigate the mixing of frequencies in the formation region due to the primary Strouhal vortex and the separated shearlayer secondary eddies. Results from a simulation at Re = 5600 will also be presented of the organized vortex motion in the near wake of the circular cylinder with special emphasis placed on the turbulent statistics of the formation region.
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From page 583... ...
stress tensor Ok is defied in terms of the Cartesian and contravariant velocity componentsas`,k=uiUk- UiUk. -For the cylinder and hydrofoil formation regions, the LES system of equations in (3 and 4)
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From page 584... ...
RESULTS AND DISCUSSION Simulation of the cylinder flow was focused specifically on resolving the separated shear layer physics and the formation and transport of me Strouha1 vortices. To establish sufficient grid resolution near the cylinder surface, comparisons were made to the experimental results reported by Bouard and Coutanceau (16)
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From page 585... ...
In contrast to their relative size, the detection frequency of the Strouhal vortices displayed considerable variability. Figure 6 is a good illustration of this characteristic where a nonuniform streamwise and relative transverse spacing can easily be seen between subsequent vortices.
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From page 586... ...
Conversely, the time signal of the drag force coefficient displays periods of intermittence and bursting phenomena which can largely be attributed to the numerous mixed modes occurring in the separated shear layers (2~. The corresponding frequency spectra reflect these characteristics by indicating dominate peaks at several frequencies and over broader bandwidths.
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From page 587... ...
compared to an angle of 50 degrees for the present Re = 5600 results. Presentation of the LES results at Re = 8000 begins with a typical snapshot of the vorticity contours inside the formation region as shown in Figure 11 where the dashed contours denote negative 587
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From page 588... ...
with Is = 0.112. Although Figure 12 indicates two areas of highest peak amplitude in the formation region, only one can be perceived as within the separated shear layer.
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From page 589... ...
At AOA = 7.5° (Figure 14) , a separation bubble was produced through laminar separation along the upper surface followed by reattachment due to an abrupt transition to turbulence of the separated free-shear layer.
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From page 590... ...
8. Preliminary LES results of a NACA 0018 hydrofoil showed laminar separation of the upstream upper boundary layer followed by transition to turbulence in the separated shear layer and finally reattachment near the beginning of the trailing edge.
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From page 591... ...
and Triantafyllou, G.S., 1992, "Three-Dimensional Dynamics and Transition to Turbulence in the Wake of Bluff Bodies,"Journal of Fluid Mechanics, Vol.
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