(c) 25 μm (d) 50 μm
Fig. 3 The distribution of the time-averaged pulse velocity along the
normal direction
Fig. 3 shows that the distribution of the normal pulsation intensity of
oil with different particle sizes along the normal direction is roughly
in the shape of a ”W”. The amplitude of the normal pulsation intensity
in the central region and the near-wall region is largely within the
field of view tested by PIV; moreover, the particle concentration has a
non-unidirectional effect on the distribution of the normal pulsation
intensity. The normal pulsation intensity is also affected by the wall
of the pipeline, but the distribution of the normal pulsation intensity
shows a parabolic shape due to the action of the central mainstream.
Fig. 3 (a) shows the effect of different
particle concentrations on the distribution of the normal pulsation
intensity when the particle size is 5 μm. The particle concentration
(6.58 ppm and 14.40 ppm) is larger and the variation in the normal
pulsation intensity of the oil is greater in the near-wall area. In
contrast, when the particle concentration (0.65 ppm, 0.97 ppm, and 3.00
ppm) is smaller, the variation range of the normal pulsation intensity
in the central region is greater. This finding is because increasing the
particle concentration makes the wall surface prone to the rough
surface, and this effect enhances the turbulent burst behavior near the
wall, thus leading to a significant increase in the normal pulsation
intensity near the wall(Li et al., 2012).
Fig. 3 (b) shows the distribution of the normal pulsation intensity of
the oil under the diameter of 15 μm particle size along the normal
direction. The influence of different particle concentrations is similar
to that of 5 μm. Figs. 3 (c) and (d) show that as the particle size
increases, the amplitude of the normal pulsation intensity increases
slightly, which indicates that the particle size has an influence on the
normal pulsation intensity of the oil. Fig. 3 (c) shows that due to a
decrease in the viscous shear force of 25 μm particles in the near-wall
region, the distribution of the oil normal pulsation intensity for the
different particle concentrations increases with increasing particle
concentration. However, in the central region, due to the central
mainstream, the retardation role of the particles increases, so the
normal pulsation intensity decreases as the particle concentration
increases.