Study of granular state transition in a rotation drum by using speckle visibility spectroscopy and the edit distance with real penalty algorithm

摘要

The states and in-between transitions of granular flows in a horizontal drum is difficult to identify by using the conventional surface slope angle. In this work, we employed the Speckle Visibility Spectroscopy (SVS) method to measure the fluctuation of particle velocity, delta v(2) (i.e. the so-called granular temperature). By analyzing characteristics of delta v(2), we defined discrete avalanche, transition regime and the continuous flow. By using the Edit Distance with Real Penalty method to quantitatively measure the periodicity, we found that particle motion in passive layer of the granular flow has a transition regime consistent with the active layer, and the active layer undergoes discrete avalanche (DA) as the drum rotates at a low rotational speed (<0.063 RPM). As rotation speed is >0.103 RPM, the active layer undergoes a continuous flow (CF). When the rotation speed is between DA and CF, DA and CF are found occur alternately. We defined this state of the granular flow as the transition state. With the periodicity as the key parameter, the transition regime can be quantitatively identified, and the transition regime and the critical speed of DA and CF are obtained. The method of period detection is further extended to DA and CF. We found that in DA, the periodicity of particle motion increases with the increase of Froude number and reaches the maximum when it was close to the transition regime. In the CF, no significant periodicity was found. Meanwhile, through quantitative measurement of the transition state, we found the main factors affecting the transition state range during the filling degree. These findings shows that the periodicity of particle motion can accurately identify the three states of granular flows. (C) 2019 Elsevier B.V. All rights reserved.