Toshihiro Takami

Numerical Experiment of Thermoset Particles in Surface Modification System with Discrete Element Method (Quantization of Cohesive Force Between Particles by Agglomerates Analysis)

Numerical simulations using the discrete element method with similar particle assembly model are performed for the surface modification process of thermoset particles. In the simulations, the cohesive force between particles and the effect of thermophoresis are examined numerically in a particle dispersion system. Simulations are also carried out for different gas dispersion velocities. By varying the dimensionless parameter associated with the cohesive force, average agglomerate diameter increases as the cohesive force between particles increases. To the end, it is demonstrated that the cohesive force between particles can be quantitatively determined if the average agglomerate diameter is experimentally or numerically obtained.

Drag Reduction of Turbulent Flows in a Curved Pipe due to the Swirling Instability

The effect of the introduction of swirling motion into turbulent flow in a curved pipe is studied experimentally. The friction of the flow in a straight pipe is known to increase as the introduced swirling motion intensifies. In the present study, it is found that the friction in a curved pipe is reduced when weak swirling motion is provided. In order to investigate this drag reduction, velocity distributions are measured at some cross sections in the curved pipe by use of the rotating probe technique with an inclined hot-wire. Detailed measurements of the velocity field reveal that interesting swingback phenomena appear as the vortical flow structure develops from the entrance of the pipe, which may cause the drag reduction in case of weak swirls.

Near-Wall Turbulence of Drag Reduction and Promotion in Unsteady Turbulent Pipe Flows

An unsteady behavior of the wall-drag, the velocity and the turbulence is experimentally investigated in the unsteady turbulent pipe flow, under several flow conditions with a rapid to slow time-variation and a large distortion of the flow-rate imposed stepwise. The instantaneous wall-shear stress and three-components of instantaneous velocities are simultaneously measured using the HWA technique of a surface hot-wire and a non-orthogonal triple-sensors probe. In the present study, to understand the unsteady behavior of the relation between the wall-drag and the velocity distribution, the unsteady response of the turbulence to the imposed unsteady flow is investigated by analyzing the relation between the unsteady Reynolds stress and the instantaneous velocity fluctuation during the accelerating and decelerating phase. It is found that, near the pipe-wall, the statistical parameter of the phase-average turbulence structure and the phase-average quadrant contribution rate of instantaneous velocity fluctuations to the Reynolds stress are almost similar to those in the steady turbulent flow, although the drag-reduction and the drag-promotion occurs during the accelerating and decelerating phase respectively.Copyright