Multiscale Turbulence Characteristics of Gas–Liquid Pressure Fluctuations in an Industrial Quatro Static Mixer

The gas–liquid two-phase flow is of great significance to industrial production. The nonlinear turbulence characteristics of pressure fluctuation in a Quatro static mixer (QSM) are experimentally investigated under different superficial gas/liquid velocities to further study the flow characteristics of the gas–liquid two-phase. It is shown that there is a generalized self-similarity scaling law in the QSM, which is obtained by fitting the structure function of pressure fluctuation signals at different inlet and outlet flow velocities. Through self-similarity scaling law analysis, the scaling exponent parameters of the structure function of two-phase flow pressure fluctuation under apparent liquid velocity (UL) = 0.028 m/s and different apparent gas velocities (UG) in QSM are calculated. The calculation results show that the singular scaling exponent (γ) and intermittency parameter (β) are in the ranges of −0.142–0.311 and 0.286–0.966, respectively. This indicates that there exists an extended self-similarity scaling law in QSM under a low Reynolds number (Re). The R/S and autocorrelation analysis reveal that the detailed signals at the inlet and outlet have three similar flow behaviors, which consist of the liquid turbulence at the inlet, the bubble movement, breakup and coalescence, and the liquid swirling flow. The nonlinear analysis shows that flow in QSM presents a pseudohomogeneous flow pattern when the Hurst index (H) = 0.4–0.6, while it presents a heterogeneous flow pattern when H = 0.6–0.72. Support vector machine (SVM) and Random Forest models (RF) are utilized to better predict the flow pattern, with the recognition precision reaching 99.08 and 99.39%, respectively.