Large scale structures of turbulent flows in the atmospheric surface layer with and without sand

This paper reports an investigation of the effects of rough forward facing steps on turbulent flows. The surfaces of the rough steps were covered with sandpapers. A particle image velocimetry technique was used to conduct measurements at the mid-plane of the test section and at several locations downstream to 68 step heights. A Reynolds number of Reh = 4800 and δ/h = 4.7 were employed, where h is the mean step height and δ is the incoming boundary layer thickness. The results indicate that mean reattachment length decreases with increasing roughness. In addition, the effect of the step roughness decreases with downstream distance. The proper orthogonal decomposition results showed that the step roughness affects even the large scale structures. Furthermore, the reconstructed turbulence quantities suggest that the step roughness suppresses the large scale turbulence.

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On Accurate Experimental Measurements of the Dynamics of Large Scale Structures in Turbulent Flows

IUTAM Symposium on Turbulent Mixing and Combustion - Fluid Mechanics and Its Applications ◽

10.1007/978-94-017-1998-8_6 ◽

2002 ◽

pp. 73-83

Author(s):

Dan Ewing ◽

Scott Woodward

Keyword(s):

Turbulent Flows ◽

Large Scale ◽

Experimental Measurements ◽

Large Scale Structures ◽

Scale Structures

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Numerical Simulation of Unsteady Turbulent Flow in Axisymmetric Sudden Expansions

Journal of Fluids Engineering ◽

10.1115/1.1374441 ◽

2001 ◽

Vol 123 (3) ◽

pp. 574-587 ◽

Cited By ~ 38

Author(s):

Baoyu Guo ◽

Tim A. G. Langrish ◽

David F. Fletcher

Keyword(s):

Numerical Simulation ◽

Turbulent Flows ◽

Large Scale ◽

Critical Value ◽

Expansion Ratio ◽

Large Scale Structures ◽

Inlet Swirl ◽

Scale Structures ◽

Reported Data ◽

Oscillation Frequencies

This paper is concerned with the numerical simulation of unsteady turbulent flows behind sudden expansions without inlet swirl. Time dependent simulations have been carried out using the VLES approach with the standard k-ε model. The expansion ratio investigated is in the range from 1.96–6.0. The simulations show that the flows in axisymmetric sudden expansions are inherently unstable when the expansion ratio is above a critical value. The precessing phenomenon, which features self-sustained precession of the global flowfield around the expansion centerline, is predicted successfully using CFD, with simulated oscillation frequencies that are in general agreement with reported data. For the case of expansion ratios from 3.5–6.0, a combination of a precession motion and a flapping motion in a rotating frame of reference is predicted in terms of the jet movement. Large-scale structures are identified in the downstream flowfield. Other important phenomena, such as the transition of the oscillation patterns, have also been predicted.

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Some comments about observations and image processing of comet 29P/Schwassmann-Wachmann 1

International Astronomical Union Colloquium ◽

10.1017/s0252921100031493 ◽

1999 ◽

Vol 173 ◽

pp. 243-248

Author(s):

D. Kubáček ◽

A. Galád ◽

A. Pravda

Keyword(s):

Image Processing ◽

Large Scale ◽

Harvard College ◽

Oak Ridge ◽

Large Scale Structures ◽

Short Period Comet ◽

Short Period ◽

Scale Structures ◽

Harvard College Observatory ◽

Period Comet

AbstractUnusual short-period comet 29P/Schwassmann-Wachmann 1 inspired many observers to explain its unpredictable outbursts. In this paper large scale structures and features from the inner part of the coma in time periods around outbursts are studied. CCD images were taken at Whipple Observatory, Mt. Hopkins, in 1989 and at Astronomical Observatory, Modra, from 1995 to 1998. Photographic plates of the comet were taken at Harvard College Observatory, Oak Ridge, from 1974 to 1982. The latter were digitized at first to apply the same techniques of image processing for optimizing the visibility of features in the coma during outbursts. Outbursts and coma structures show various shapes.

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