1987 Volume 22 Issue 5 Pages 355-363
A detail study on suspension phenomena of particles from wall surface was conducted to develop a model for simulation purposes. The renewal model, proposed by Nakagawa etal., was adopted to express the bursting phenomena of cyclic motion since the suspension of particles is initiated by the motion of fluid near the wall surface. It was shown that the local ejection current could be described well by the model.
A mathematical model was developed for each of the three mechanisms for initiation of the movement of particles; these being sliding, rolling and lift-up. Critical friction velocity at which the particle starts to move was estimated for each of these three forms of mechanisms by using models.
The investigation has shown the following; the model for motion in sliding form is capable of simulating the experimental results that the minimum critical friction velocity is observed at the particle diameter of approximately 0.01 cm, the model for motion in rolling form can describe the effect of surface roughness, and the model for motion in lift-up form, which includes the newly proposed lifting ability index, can quantitatively simulate that smaller particles tend to start the motion due to lift-up than sliding.
