We experimentally investigate the effect of interfacial waves on the gas flow in a stratified gas/liquid pipe system. This study is using a combination of three different experimental methods:
Particle Image Velocimetry (PIV) measures spatially resolved velocity profiles, both mean and turbulent, in both the gas and liquid phase simultaneously.
Interfacial elevation measurements using Conductance Probes (CP) provides interfacial flow pattern statistics such as wave heights and wave frequencies.
Hot-Wire Anemometry (HWA) measures turbulent fluctuations in the gas-phase with high temporal resolution providing turbulence spectra at given points in the flow.
This approach shows that a wavy interface induces dynamic fluctuations in the gas flow at the exact same frequency as the dominant wave frequency. This is a direct consequence of the continuity principle. Also, in the higher frequency region of the turbulence spectra, we see that the rate of decay with which turbulent energy cascades is clearly influenced by the local interfacial flow pattern. This indicates that the interaction between the gas flow (the wind) and waves produce energy containing eddies which interact with the turbulent field of the gas flow.
Stratified gas/liquid flow is a flow regime that is often in industries such as petroleum, chemical processing and nuclear. This specific flow regime occurs when the flow rate of each phase is low enough, i.e. below the onset of intermittent flows such as slug flow or dispersed flow. Even though stratified flow is a less harmful flow regime with regards to the production infrastructure than, for instance, slug flow, it has been a subject of investigation for the last few decades, both within academic and industrial multiphase flow communities. One of the reasons for this is that its underlying physics, portrayed by the complex interplay between the turbulent structure of either phase and the interfacial flow pattern, are still far from understood. Another reason is that stratified flow may develop into hydrodynamic slug flow if the local conditions are appropriate because of a series of turbulence-wave and wave-wave interactions (11). Further understanding of the underlying mechanisms that govern stratified flow is certainly needed to develop next generation two-phase flow models, which will perform successfully under different boundary and initial conditions.
The main task of multiphase flow models is to close the equations which are used when predicting system parameters that are important for design and operation of production systems and overall production chain. Some of the most important parameters can be listed as the pressure drop, liquid holdup and transition to intermittent flow regimes.
