An experimental study on turbulence modification in the near-wall boundary layer of a dilute gas-particle channel flow

Sand-turbulence interaction in a high-Reynolds-number turbulent boundary layer under net sedimentation conditions

“…p,rms + > f,rms + and p,rms + > ,rms + . This is consistent with previous studies on particle-laden channel flows Tanière et al 1997;Li et al 2012;Coletti et al 2016), and can be attributed to the combined effect of the gravity and the turbulent flow.…”

“…and Δz is the laser-sheet thickness. Similar to Li et al (2012), the fluctuating velocity of sand grains is defined with respect to the ensemble-averaged value within the local sub-box, i.e.…”

“…strength and length/time scales, are also susceptible to particle motions. Such particle-induced structural modifications have been observed in busting events (Rashidi et al 1990;Pan and Banerjee 1996;Kaftori et al 1998;Li et al 2012), inner-layer quasi-streamwise vortices (Dritselis and Vlachos 2008) and low-speed streaks (Li et al 2016). However, similar to the turbulence modification, remarkable conflicts in the previous studies on this issue still exist.…”

“…Secondly, the crossing trajectory effect, induced by heavy particles falling out from turbulent eddies (Csanady 1963), is strengthened by large slip velocity between two phases (see figure 7a). Li et al (2012) suggested that the crossing trajectory effect might contribute to the reduction of the spatial scale of turbulent coherent structures. It will be shown in §5 that the presence of sand grains suppresses the sweep and ejection events in the near-wall region, providing a side support for this effect.…”

“…However, similar to the turbulence modification, remarkable conflicts in the previous studies on this issue still exist. For instance, Dritselis and Vlachos (2008) found that heavy particles increased the streamwise extent of quasi-streamwise vortices, while Li et al (2012) and Li et al (2016) reported that heavy particles preferred to reduce the coherency of near-wall vortical structures.…”