TAILIEUCHUNG - PARTICLE-LADEN FLOW - ERCOFTAC SERIES Phần 10

Tham khảo tài liệu 'particle-laden flow - ercoftac series phần 10', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Particle sedimentation in wall-bounded turbulent flows 381 was used for the normal direction with Az at the wall and Az 7 at the center of the channel. The particles were released homogeneously distributed in a plane at a distance z H from the bottom of the channel which corresponds to z 450 with an initial vertical velocity equal to Vt . For each particle we computed the time it took to travel i from z 450 to z 250 center of the channel ii from z 250 to z 50 buffer region and iii from z 50 to z 3. Particle Froude number Fig. 8. Average settling velocity for an open-channel as a function of the particle Froude number. The results for different particle Froude numbers are presented in figure 8. When the particle Froude number was smaller than 1 and when the particles were falling down between z 450 and z 250 and between z 250 and z 50 the average settling velocity Vs was higher than Vt. In this case the relation between Vs and Fp is somehow similar to the case of a vortex array where the vortex distance is large 8Rv with an almost monotonic decrease in the average settling velocity as Fp increases. On the other hand in the near-wall region there is a maximum in the average settling velocity at Fp 1. In the vortex array case we saw that for intermediate values of Fp the average settling velocity had a strong dependence on the vortex spacing with a more complex behavior when the vortex spacing was smaller. Near the wall the streamwise vortices play an important role and their spacing is smaller than further away from the wall 6 . This could be a possible explanation for the behavior near the wall. However the behavior is quite different from the compact vortex array D 4Rv and contrary to the vortex array Vs is always higher than Vt. Clearly the turbulence structure appears to play an important role in determining the settling velocity. In order to quantify the importance of the turbulence structure on the particle motion we analyzed the particle-fluid .

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