(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.