(c) 25 μm (d) 50 μm
Fig. 2 The distribution of streamwise mean intensity along the normal
direction
Fig. 2 (a) shows the distribution of the
flow pulsation intensity of the oil along the normal direction with
different particle concentrations for a particle size of 5 μm. The
figure shows that the flow pulsation intensity of the PIV acquisition
oil field is relatively slow to change along the normal distribution in
the central region due to the presence of particulate matter, while the
change is steep in the near-wall area, and this trend becomes
increasingly obvious as the particle concentration increases. On the
other hand, when the particle concentration is lower, the flow pulsation
intensity of the oil field is larger in the near-wall area and gradually
decreases toward the center of the pipe; however, this trend becomes
less obvious as the particle concentration increases. On the whole, with
increasing particle concentration, the flow pulsation intensity of the
oil successively decreases, and if the particle concentration is too
large (such as 6.58 ppm and 14.40 ppm), the difference in flow pulsation
intensity is smaller. The reason is that the particles in oil in the
near-wall area increase the flow velocity of the oil. To maintain mass
conservation, the oil flow velocity in the central region decreases.
Additionally, coupled with the blocking action of the oil particles, the
flow pulsation intensity of the oil is steeply distributed in the
near-wall region along the normal direction, while this intensity is
relatively gentle in the center area(Ling and Zhong, 1999). In addition,
with increasing particle concentration in oil, the effect of near-wall
particles on oil flow velocity growth is attenuated due to decreasing
viscous shear force, which weakens the tendency of oil flow pulsation
intensity growth in the near-wall area. Therefore, as the particle
concentration reaches 3.00 ppm or more, the tendency of the flow
pulsation intensity distribution along the normal direction becomes
slower. This finding also indicates that the flow pulsation of the flow
field in the pipeline is greatly affected by the wall surface.
According to the effect of the 15 μm particle size on the flow pulsation
intensity of oil shown in Fig. 2 (b), the effect of different particle
concentrations on the intensity distribution along the normal direction
is basically consistent with that of the 5 μm particle size shown in
Fig. 2 (a). The difference is that in the case of low particle
concentration, the maximum value of the flow pulsation intensity is
larger for the case of the 15 μm particle size. For example, the maximum
value of the flow pulsation intensity for the 5 μm particle size under
0.65 ppm particle concentration is 0.233, while the maximum value of the
flow pulsation intensity for the 15 µm particle size is 0.236. The
reason is that the larger the particle size is, the greater the viscous
shearing force of the oil, so the particles in the near-wall region
increase the role of oil flow velocity growth.
Fig. 2 (c) shows the effect of different
particle concentrations on the flow pulsation intensity of the oil when
the particle size is 25 μm. The effect of the 25 μm particle size on the
flow pulsation intensity of the oil is similar to the trends in Fig. 2
(a) and (b). However, for the case of the particle size of 25 μm, the
flow pulsation intensity is larger in the near-wall region and has a
value of 0.256, and then, the 5 μm and 15 μm amplitudes are increased by
9.95% and 8.56%, respectively. In addition, when the particle
concentration is 6.58 ppm, the flow pulsation intensity of oil is
larger, and this finding indicates that the particle size in the oil has
less attenuation effect on the viscous shear force of oil when the
particle size is 25 μm. However, the effect of the particles in the
near-wall area on the oil growth rate is enhanced when the particle size
exceeds 25 μm, as shown in Fig. 2 (d). When the particle size is 50 μm,
the amplitude of the flow pulsation intensity under each particle
concentration decreases greatly, except for the particle concentration
of 0.65 ppm. Moreover, when the particle concentration is 6.58 ppm, the
flow pulsation intensity is basically the same as that for 14.40 ppm.
The results in Fig. 2 show that the flow pulsation intensity decreases
with increasing particle concentration, and the difference decreases
gradually for oil with different particle concentrations.