Characterization of pressure fluctuation in swirling gas-solid two-phase flow in a horizontal pipe

In order to analyze the features of pressure fluctuation and to interpret particle flow pattern transitions in both Fourier and physical spaces, the experimental wall pressure fluctuations in swirling gas-solid two-phase flows are analyzed by statistical analysis and wavelet transform. Our experiment is carried out in a horizontal pipe with a length of 7.5 m and an inner diameter of 76 mm. The initial swirl number based on the total inflow was varied from 0.0 to 0.61, the mean gas velocity was varied from 6 to 28 m/s and the solid mass flow rate was varied from 0.08 to 0.5. We discovered that the amplitude of pressure fluctuation in the axial gas-solid flow is larger than that of the swirling gas-solid flow at low gas velocity and the amplitude of the swirling gas-solid flow decreases when increasing the initial swirl number within the range of low gas velocity. With increasing initial swirl intensity, the strong peaks of the power spectral density function (PSD) become smaller and the magnitudes of PSD decrease as a whole. We can say that the swirling gas-solid flow is very effective in reducing the unstable flow. From the wavelet analysis of pressure fluctuations, the unsteady characteristics of swirling gas-solid two-phase flows were revealed over a two-dimensional time-frequency plane. The distribution of wavelet coefficients indicates the fluctuation of particle velocities and concentrations with time and scales. At low air velocities, a periodic oscillation appears in wavelet coefficients around 0.5 Hz, which may be interpreted as the existence of dunes along the bottom of the pipe at nearly constant intervals. The dominant frequency of the suspension flow increases along the flow direction and reaches 110 Hz in the fully developed region.