Direct numerical simulation of finite sized particles settling for high Reynolds number and dilute suspension

Finite sized particles settling under the action of gravity are investigated by immersed boundary method for dilute suspensions and low to high range of Reynolds number. The Reynolds number based on the terminal velocity of a single particle is varied from 1 to 300 and the solid volume fraction (φ) is varied from 0.005 to 0.05. The studied range of Reynolds number corresponds from streamlined flow to downstream vortex shedding flow for single particle. For φ = 0.005, 0.01 and high Reynolds number (Re ≧ 175), settling particles clusters due to the entrapment in high fluid shear regions. However for Re = 50 and 100, particles form separated pairs due to relatively weak strength of wakes that promote to drafting-kissing and tumbling scenario. These particle structures at high Reynolds number changes the settling behaviors of particles e.g. increase in the settling velocity and fluid velocity fluctuations. For φ = 0.03, 0.05, hindered settling effects dominate and reduce the effects of particles clustering due to Reynolds number.