Abstract
A turbulent channel flow laden with elongated, fiber-like particles is investigated experimentally by optical techniques. The flow-particle inter-coupling is analyzed in the case of particles with an aspect ratio of 40 and 80, at two volume fractions, 10−5 and 10−4. An image processing technique is presented, which is employed to simultaneously obtain carrier flow velocimetry data and distribution and orientation data of dispersed particles. Turbulence enhancement is reported in the near-wall region, with a higher level of increase associated with higher aspect ratio particles. Comparison to fiber data suggests that this mechanism of turbulence modulation stems from a particles orientational behavior. The preferential particle distribution is reported to be dependent on the aspect ratio in the region close to the wall. The probability density function of the fibers’ orientation angle appears to be independent of the particle aspect ratio once it is conditioned to the fibers’ characteristic size.
Highlights
Phenomena of transport and dispersion of non-spherical, anisotropic particles in turbulent flows are ubiquitous in industrial processes and applications
The dispersed phase has a negligible effect on carrier flow turbulence, whereas the flow action on the particle phase may lead to the onset of phenomena such as preferential particle concentration and accumulation
A relevant role appears to be played by the fiber aspect ratio, with a larger increase in turbulence fluctuations associated with higher values
Summary
Phenomena of transport and dispersion of non-spherical, anisotropic particles in turbulent flows are ubiquitous in industrial processes and applications. The dispersed phase has a negligible effect on carrier flow turbulence, whereas the flow action on the particle phase may lead to the onset of phenomena such as preferential particle concentration and accumulation (one-way coupling). Particle preferential distribution and orientation has particular relevance for specific applications, such as the papermaking industry, where it is paramount to predict the spatial location and the orientation state of particles within the flow This aspect dramatically influences the rheological properties of the product and its quality. As the volume fraction of dispersed particles increases, inter-particle effects start to occur and four-way coupling between phases occurs. This regime will not be discussed in this manuscript
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