Transitional and Turbulent Flow in a Bed of Spheres as Measured with Stereoscopic Particle Image Velocimetry

Abstract

Stereoscopic particle image velocimetry has been used to investigate inertia dominated, transitional and turbulent flow in a randomly packed bed of monosized PMMA spheres. By using an index-matched fluid, the bed is optically transparent and measurements can be performed in an arbitrary position within the porous bed. The velocity field observations are carried out for particle Reynolds numbers, Re p , between 20 and 3220, and the sampling is done at a frequency of 75 Hz. Results show that, in porous media, the dynamics of the flow can vary significantly from pore to pore. At Re p around 400 the spatially averaged time fluctuations of total velocity reach a maximum and the spatial variation of the time-averaged total velocity, u tot increases up to about the same Re p and then it decreases. Also in the studied planes, a considerable amount of the fluid moves in the perpendicular directions to the main flow direction and the time-averaged magnitude of the velocity in the main direction, u x , has an averaged minimum of 40% of the magnitude of u tot at Re p about 400. For Re p > 1600, this ratio is nearly constant and u x is on average a little bit less than 50% of u tot . The importance of the results for longitudinal and transverse dispersion is discussed.

Investigation of Post-Darcy Flow in Thin Porous Media

“…However, it can still be observed that the size of the vortices for the confined porous media is larger than those in the non-confined case. Such a behavior was previously reported for a confined porous media in Khayamyan et al (2017aKhayamyan et al ( , 2017b through their experiments carried out on transition and turbulent flow in a random packed bed of spheres. They observed that the non-uniformity in the mean velocity profile within the pores increases at first with an increase in Re, while the mean velocity distribution within the pores becomes more uniform at higher Re.…”

“…They observed that the non-uniformity in the mean velocity profile within the pores increases at first with an increase in Re, while the mean velocity distribution within the pores becomes more uniform at higher Re. Khayamyan et al (2017aKhayamyan et al ( , 2017b also reported that such variations may also be reflected in macroscopic properties of flow such as volume-averaged hydrodynamic dispersion and pressure drop.…”

Modelling heat transfer during flow through a random packed bed of spheres

“…Naturally, the temperature front in the discrete model is not straight as in the CFD model as also shown in Ljung et al [31]. This is because of the natural dispersion in the system due to the arrangement of the pellets and the uneven velocity distribution as disclosed numerically in Frishfelds et al [14] and experimentally in Khayamyan et al [21,22].…”

Investigation of Hydrodynamic Dispersion and Intra-pore Turbulence Effects in Porous Media

“…Also, in the cases of = 0.8 and = 0.95 , a slight increase is observed with the increase in Re from 150 to 1500 followed by a decrease as the Re is increased to 15,000. Such a trend is observed for the nonuniformity in the spatial distribution of time-averaged velocity in Khayamyan et al (2017a). In their work, the initial increase with Re is attributed to the enhancement of inertial effects as the flow regime changes from creeping flow to transitional regime while the subsequent reduction with an increase in Re is assumed to be due to the turbulence effects becoming dominated which enhance mixing resulting in more uniform distribution.…”