Pseudoturbulence in bubbly and transition flow regimes

Abstract

Computational fluid-dynamics codes use the two-fluid model to simulate transport phenomena in liquid–gas flows. Numerical instabilities arise when flow regime transition occurs, i.e. bubbly flow to slug flow. One mechanism that produces the transition between regimes is the fluctuation induced over the liquid phase velocity due the relative movement of ascending bubbles. Using multi-tip impedance probe and Laser Doppler Anemometry (LDA), the main local flow parameters of the two-phase flow were obtained. The flow conditions selected were single phase flow up to liquid–gas flow at 30 % gas concentration. The power spectral energy distributions obtained show that turbulence intensity and the energy exponent decay have a nearly constant value when wall peak is observed (wall peak distribution occurs when the radial void fraction distribution shows a peak concentration near to the channel wall). Under the flow conditions tested, pseudo-turbulence effects can be observed at low gas concentrations in bubbly flow regime and the decay energy has a nearly constant slope; whereas at transition and slug regimes the exponent decay in PSD's shows a non-constant value, and the lift force would be less important.