Experimental determination of saltating glass particle dispersion in a turbulent boundary layer

Wang, Hong Tao; Zhang, Xiao Hang; Dong, Zhi Bao; Ayrault, M.

doi:10.1002/esp.1376

Cited by 12 publications

(7 citation statements)

References 33 publications

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“…Le plancher de la soufflerie fut recouvert de particules sur une épaisseur de 0,02 m, à une distance de 8 m en aval de l'entrée et sur une longueur de 3 m. Les mesures par visualisation et analyse d'images [4] furent effectuées dans une section où la couche de saltation est stationnaire et établie. Un descriptif complet des expériences et des résultats expérimentaux peut être trouvé dans Zhang et al [5] et Wang et al [6].…”

Section: Version Française Abrégéeunclassified

Experimental determination of the concentration Probability Density Function for a saltating particle layer

Zhang¹,

Wang²,

Dong³

et al. 2005

Comptes Rendus. Mécanique

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A horizontal saltation layer of glass particles in air was investigated experimentally in a wind tunnel. Particle concentrations are measured by light scattering diffusion and image processing and all the statistical characteristics were evaluated and thus the probability density function. Our experimental results confirm that the mean concentration decreases exponentially with height, the mean Eulerian dispersion height H being a characteristic lengthscale and that the instantaneous concentration distribution c( x, t) is a random variable following quite well a lognormal distribution. To cite this article: X.

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Section: Version Française Abrégéeunclassified

Experimental determination of the concentration Probability Density Function for a saltating particle layer

Zhang¹,

Wang²,

Dong³

et al. 2005

Comptes Rendus. Mécanique

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“…The measuring area was set at 3 m from the upwind edge of the particle bed, the saltation layer being statistically stationary but not saturated. As explained in detail by Wang et al (2006), although the short distance x = 3 m does not achieve the equilibrium state, it can ensure a significant development of a saltating cloud (Dong et al, 2004). Absolute values are different, but due to the physical saltation process we can expect that the non-dimensionalized results obtained in the 'overshooting' stage are identical to the equilibrium stage (Shao and Raupach, 1992).…”

Section: Methodsmentioning

confidence: 98%

“…A complete description of the facility can be found in the work of Dong et al (2002) and Wang et al (2006). The boundary layer develops on the horizontal flat floor of the 1 m × 0·6 m (width × height) test section of the wind tunnel.…”

Section: Methodsmentioning

confidence: 99%

“…A detailed description of this technique can be found in the work of Ayrault and Simoens (1995) and Wang et al (2006). As discussed in detail by Ayrault and Simoens (1995) for polydispersed incense particles using Mie scattering diffusion (Kerker, 1979), the grey level of the scattered light is proportional to Σd i 2 N i , where N i is the number of particles of diameter d i and the subscript i denotes the ensembles of different particle diameters in the total sample.…”

Section: Methodsmentioning

confidence: 99%

“…For the 1:9 ratio, many saltating and dust particles are lifted off the bed surface; the concentration profile resembles a typical saltation profile (Wang et al, 2006) and shows an exponential shape. As the saltation process is more inefficient for the 2:8 ratio, the results are quite similar to the 'pure dust' configuration and the mean concentration profile exhibits a power shape.…”

Section: Dust Entrained By Saltating Particlesmentioning

confidence: 96%

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Vertical dispersion of dust particles in a turbulent boundary layer

Wang¹,

Zhou²,

Dong³

et al. 2007

Earth Surf Processes Landf

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The flow of glass dust particles in air was investigated experimentally over a flat bed in a wind tunnel. Particle concentrations were measured by light scattering diffusion (LSD) and digital image processing. It was verified that saltation is the main mechanism for ejection of dust particles. Vertical mean dust concentrations for 'pure dust' and two mixtures of dust and saltating glass particles were determined and analysed. The experiments confirmed that for the 'pure dust' configuration the mean concentration decreases as a power function with height. For the mixture configurations and for free stream velocities close to the threshold velocity, the mean concentration also decreases in a power function. For higher velocities, mean concentration decreases respectively as a power function or exponential function for large and small ratios of the dust:saltating particles respectively. The exponent of the power law reflects the dust:particle ratio and the free stream flow velocity. Figure 4. Vertical mean concentration profiles of 'pure dust' expressed in grey level values versus height (pixels) for U e = 8 m s −1 , for the three different averages 1-300, 300-600 and 600-800.dust particles from the newly prepared bed, so the dust flux will be intense at the beginning of the process and will decrease with time up to the bed stabilization, where few dust particles are available and entrained. This is a well known phenomenon first described by Bagnold (1941). This bed stability is caused by cohesive forces between dust particles; the ratio of cohesive to aerodynamic force increases rapidly as particle size decreases (Greeley and Iversen, 1985). Note that for smaller velocity the removal is slow; the bed is not stabilized. If we recorded the images over a longer time, concentration will decrease with time. Figure 5. Vertical mean concentration profiles of 'pure dust' expressed in grey level values versus height (pixels) for U e = 12 m s −1 , for the three different averages 1-300, 300-600 and 600-800.Figure 9. Examples of instantaneous (a), (b) and mean (c) images at U e = 11 m s −1 . The black lines correspond to the particle bed level. Flow is from right to left. Dimensions of the images: 82 mm × 82 mm.Figure 11. Normalized mean concentration profiles / max as a function of z/H d for the 1:9 mixture. Dashed line, best power law fit (U e = 8 m s −1 ); solid line, exponential fit (U e = 9 m s −1 ).Figure 12. Normalized mean concentration profiles / max as a function of z/H d for the 2:8 mixture. Dashed lines, best power law fit (U e = 8 m s −1 ); solid line, exponential fit (U e = 9 m s −1 ).

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