| Immiscible multi-fluid flows are of great industrial importance. The nature of such flows and their stability is the topic of study here. Results of the present study has are prescribed in two parts. First part discusses the two layer fluid flows in pipe geometry while the second part looks in the properties of two layer fluid flows in inclined channel geometry.; In the first part of the work, a numerical and experimental investigation has been carried out to study the interfacial dynamics of axisymmetric liquid-liquid flows. The flow dynamics are studied as a function of the individual phase Reynolds numbers, viscosity ratio, velocity ratio, Bond number, and Capillary number. The unsteady, axisymmetric flows of two immiscible fluids have also been studied using commercial software, FLUENTRTM that uses a combination of volume of fluid (VOF) and continuous surface force (CSF) methods. For these axisymmetric multi-fluid flows, as the outer liquid flow rate is increased, the intact jet length is stretched to longer lengths while the jet radius is reduced due to interfacial stresses. The jet radius appears to increase with increasing viscosity ratio and ratio of Bond and Capillary numbers. Fully-developed (or self-similar solution) analytical model predicted multiple (one to three) solutions of jet diameter for a range of dimensionless numbers, flow rate ratio, viscosity ratio, and Bond and Capillary numbers. Experiments have been carried out using Poly Ethylene Glycol (PEG) and Canola oil to investigate the three possible branches of the analytical solutions for fully developed conditions. The measured values of inner fluid radius agree very well with the lower branch of the three branched solution whereas the deviation of the experimental results from the other two branches is observed to be significant. Numerical simulations also have been performed to compare the analytical self-similar solution results of liquid jet radius using FLUENT RTM software. The results predicted by numerical simulations agree very well with both the lower and upper branches of solution predicted for fully developed axisymmetric flows. Linear stability analysis also has been performed to identify the critical characteristics of the three branched solutions for these axisymmetric flows.; In the second part of the work, linear stability analysis of two-layer fluid flows in inclined channel geometry has been carried out to study the flow transitions and the spatio-temporal characteristics of secondary flows. Neutral stability and stability maps are generated for a range of flow conditions for which experimental measurements have been reported. Effects of flowrate, density, viscosity, and surface tension on flow instabilities also have been investigated for various values of channel inclinations. |
