Nonlinear Charakteristics of Gas-Liquid Two-phase Flow and Verification of Extended Two-Fluid Model

Void fraction distributions of air-water two-phase flow in 3 different diameter vertical tubes (0.042 m, 0.1 m, and 0.2 m) were measured by 16x16 wire-mesh sensors with a sampling frequency of 1 kHz. Also, predictions under the same flow conditions were made by a 3D extended two-fluid model, generating a time-series of cross-section averaged void fraction at the same frequency with the experiment. Fluctuation characteristics from experiments and simulations were analysed in view of the probability density function, frequency spectrum, and Trajectory Parallel Measures (TPM). The analyses of TPM showed that dynamics is well-established for large nunnles whose fiameter is on the order of Taylor wave length in an air-water system, although small bubble void fraction signal is almost random in dynamical point of view. It is shown that the fluctuation component in void fraction time series can be used as one of criteria for validation of numerical models.