Experimental study on the energy dissipation characteristics of debris flow deceleration baffles

Debris flow can cause serious damages to roads, bridges, buildings and other infrastructures.Arranging several rows of deceleration baffles in the significant influence on the mobility and deposition characteristic of debris flow. The deposit amount first increased then decreased when the flow density rises,flow path can reduce the flow velocity and ensure better protection of life and property. In debris flow prevention projects, deceleration baffles can effectively reduce the erosion of the debris flow and prolong the running time of the drainage channel.This study investigated the degree to which a 6 m long flume and three rows of deceleration baffles reduce the debris flow velocity and affect the energy dissipation characteristics. The influential variables include channel slope, debris flow density, and spacing between baffle rows. The experimental results demonstrated that the typical flow pattern was a sudden increase in flow depth and vertical proliferation when debris flow flows through the baffles. Strong turbulence between debris flow and baffles can contribute to energy dissipation and decrease the kinematic velocity considerably. The results showed that the reduction ratio of velocity increased with the increase in debris flow density,channel slope and spacing between rows. Tests phenomena also indicated that debris flow density hasand the deposit amount of debris flow density of 1500kg/m^3 reached the maximum when the experimental flume slope is 12°.

Spatial relationship between energy dissipation and vortex tubes in channel flow

The spatial relationship between the energy dissipation slabs and the vortex tubes is investigated based on the direct numerical simulation（DNS） of the channel flow. The spatial distance between these two structures is found to be slightly greater than the vortex radius. Comparison of the core areas of the vortex tubes and the dissipation slabs gives a mean ratio of 0.16 for the mean swirling strength and that of 2.89 for the mean dissipation rate. These results verify that in the channel flow the slabs of intense dissipation and the vortex tubes do not coincide in space. Rather they appear in pairs offset with a mean separation of approximately 10η.

Role of inter-particle collision on solids acceleration in riser

Collision among particles plays a significant role in governing the structure of gas-solids flow in a riser, especially in the dense and acceleration region. The inter-particle collision is the major cause not only for the kinetic energy dissipation （in terms of additional pressure drop beyond the solids hold-up） but also for the control of solids acceleration （in terms of a balancing force to prevent a free acceleration of solids）. A neglect of the balancing force of inter-particle collision against the hydrodynamic force in the solids momentum equation would simply overestimate the solids acceleration or concentration while underestimate the axial gradient of pressure along the riser by a large margin, typically by up to two orders of magnitude. This paper aims to illustrate the importance of the collision on the characteristic of the gas-solids riser flow. Our analysis shows that the collision force should be of the same order of magnitude as that of the drag force in the dense and acceleration region, which can be far beyond that of gravitational force on solids. A simple formulation of the collision force is therefore proposed to bear a similar format of drag force, with regard to the dependence upon local solids properties.With the inclusion of the proposed correlation of collision force in the solids momentum equation, our model would be able to yield reasonable phase distributions of gas-solid flows, which can be validated, in a bulk range, against available measurements of solids volume fraction and axial gradient of pressure.