气固两相流在扩径段内周期性运动减弱的功率谱分析

Figure 9 presents the power spectral density distributions of glass beads and FCC particles at different heights in the expansion section. It can be observed that the power spectral amplitudes of both particles decrease with the increase of bed height at all radial positions. The amplitude is largest at the bottom of the expansion section, and decreases significantly at heights H2 and H3. This is due to the weakening of the gas-solid interaction along the axial direction, resulting in smaller energy fluctuations in the upper part of the expansion section. Moreover, the main peak of the power spectrum gradually becomes blurred with increasing height, and no obvious main peak is observed at height H3. These phenomena indicate the weakened periodic motion of gas-solid two-phase flow along the axial direction in the expansion section, which may be attributed to the gradual smoothing of the flow as the turbulent energy dissipation increases with height. The variation of power spectral curves radially at different heights is also consistent, with the periodic characteristics of power spectra decreasing in strength from the wall towards the center of the expansion section.

It is also noteworthy that the power spectral fluctuation range of glass beads is larger than that of FCC particles at both the wall and center regions. The power spectral amplitude of glass beads is significantly higher than that of FCC particles at the bottom of the expansion section, and the main peak is more pronounced, indicating that the increase in particle density enhances the periodic flow in this region of the expansion section. In the center of the pipe, the power spectral amplitude of glass beads is lower than that of FCC particles at the bottom of the expansion section, indicating different effects of increasing particle density on the periodic flow process radially. As the height increases, the differences in power spectra between the two types of particles decrease.