Turbulence, Stability, and Imaging of Gas-Liquid Flows

The shape, location, and stability of a gas-liquid interface are studied. Linear stability analysis was used to determine flow pattern transitions. Two-equation turbulence models are adapted to fit the basestate behavior of stratified and wavy flows. The new model accounts for the interfacial roughening effects of waves and the corresponding vertical shift in the maximum velocity. A conversion from channel to pipe flow is also prescribed. Numerically, the profile is determined via an under-relaxation iteration scheme and utilizes efficient banded matrix solvers in implementing a direct method approach to the boundary value problem. These results are used in a stability analysis that incorporates the Boussinesq approximation into the Orr-Sommerfeld equation. A Chebyshev-Tau method is employed to solve the resulting eigenvalue problem. The growth rate curves provide a quantitative analysis for experimental results performed in finite pipes and also give a true neutral stability line, which is not possible to determine in the laboratory. Fundamentally, the linear stability growth rates of various waves are the necessary information needed to understand phase transitions and form the basis for non-linear studies of turbulent-turbulent flow.

An experimental investigation of dispersed multiphase flow was undertaken to determine a parameter space for gravity independent flow. The force of gravity compared to inertia, capillary pressure, and viscosity are determined by the values of the Froude, Capillary, and Stokes numbers, respectively. The bubble lengths, curvature, and film thickness were analyzed to quantify the influence of gravity on the position and shape of the interface.