Continuous wavelet analysis and proper orthogonal decomposition on particle dynamics in a horizontal self-exited gas-solid two-phase pipe flow

The high-speed particle image velocimetry is applied to measure the particle velocities of a horizontal self-exited gas-solid two-phase pipe flow with soft fins at the air velocity of the minimum pressure drop. The detailed particle dynamics of using fins' cases are analyzed and compared with a conventional non-fin case. It is found that the particle accelerating process is delayed in the acceleration regime and the vertical particle velocity is decreased near the top part of fully-developed regime due to the effect of fins' oscillations. The continuous wavelet transform of axial particle fluctuation velocity suggests that the fins make the particle motions fall into a lower frequency range in the acceleration regime. In the fully-developed regime, the dominating frequencies of large-scale particle flows are decreased and the streaks appearing in the range of high frequency are weakened by using fins. The energy distributions of proper orthogonal decomposition (POD) modes indicate that the relative energy of POD mode1 is increased by using fins in both acceleration and fully-developed regimes, and the dominance is significantly enhanced by using fins in the fully-developed regime. The auto-correlation coefficients and central frequencies of POD modes exhibit that the dominating large-scale particle motion is enhanced by using fins, correspondingly, small-scale particle motion is suppressed.

Automated summary

This study investigates the particle velocities of a horizontal self-exited gas-solid two-phase pipe flow with soft fins using high-speed particle image velocimetry. The results show that the fins delay the particle acceleration process and decrease the vertical particle velocity near the top part of the fully-developed regime. The analysis of axial particle fluctuation velocity reveals that the fins lower the particle motion frequency in the acceleration regime. In the fully-developed regime, the fins decrease the dominating frequencies of large-scale particle flows and weaken the streaks appearing in the high frequency range. The energy distributions of proper orthogonal decomposition modes indicate that the relative energy of POD mode1 is increased by using fins in both acceleration and fully-developed regimes, with a significant enhancement in the fully-developed regime. The auto-correlation coefficients and central frequencies of POD modes demonstrate that the fins enhance the dominating large-scale particle motion and suppress the small-scale particle motion.