Flow-particle coupling in a channel flow laden with elongated particles: The role of aspect ratio

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 and 10 . 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.