Majority of the fluid FLOWS in nature and industries are turbulent FLOWS. Due to their complexity, modeling and simulation of turbulent FLOWS are still among the top research topics in the field of fluid mechanics.The objective of this work is to consider the turbulence effects at the interface. The presence of interface affects the turbulence structures and they become anisotropic near the interface. In this work, the main objective is to consider the fluctuations of the interface topology and their effects on the volume fraction and the surface tension force at the interface. These effects are important under some circumstances especially when the shape of the interface changes rapidly and abruptly. The surface tension forces and the volume fraction-velocity fluctuation correlation have also important impact on the interface topology and its complicated features such as coalescence and breakup. Different new models are presented and the impacts of those parameters on the flow at the interface are presented in this work. In developing the models for mean velocity-volume fraction fluctuations the inhomogeneity of the flow at the interface is taken into account. Both Reynolds Averaged Navier-Stokes Equations and the Large Eddy Simulation Techniques were used to simulate turbulent INTERFACIAL FLOWS and implement the novel models introduced in this work. The Kelvin-Helmholtz instability, two-dimensional and three dimensional jets, and water/oil phase separation were simulated numerically and the results were compared with corresponding valid data and the accuracy of the models was examined.

Microfluidic chips in the last two decades have had significant advances in the analysis of INTERFACIAL tension phenomenon due to their many advantages. To analyze INTERFACIAL tension phenomena, droplet flow in microchannels can be used. In this study, water-n-hexane INTERFACIAL tension in the presence of surface-active agents was measured, using microfluidic tensiometry. For this purpose, a glass microfluidic flow-focusing junction was fabricated for generating n-hexane droplets within an aqueous phase. The dependence of droplet size on the concentration of surfactants has been investigated. A theoretical equation was developed, considering force balance on the droplet generation in the microfluidic device, giving a relation between the INTERFACIAL tension and the generated droplet sizes. By standardizing the microfluidic chips with the aid of a system, whose INTERFACIAL tension is known (hexane normal and tween 20 in distilled water), INTERFACIAL tension can be measured with measuring the size of produced droplets for other systems that can form droplets in the microchannel. In this study, the microfluidic device and the relation were employed to measure the INTERFACIAL tension in the presence of either of sodium dodecyl sulphate (SDS) or Cetyl trimethylammonium bromide (CTAB) surfactants. It was found that the measured INTERFACIAL tensions deviate less than 10% compared to those measured with a commercially available ring method.

The present paper deals with the study of the pressure corrections to the viscous potential flow analysis of Kelvin-Helmholtz instability with tangential electric field at the interface of two viscous fluids. Viscosity enters through normal stress balance in the viscous potential flow theory and tangential stresses for two fluids are not continuous at the interface. Here we have considered viscous pressure in the normal stress balance along with the irrotational pressure and it is assumed that the addition of this viscous pressure will resolve the discontinuity between the tangential stresses and the tangential velocities at the interface of two fluids. The viscous pressure is derived by mechanical energy balance equation and this pressure correction applied to compute the growth rate of electrohydrodynamic Kelvin-Helmholtz instability. A dispersion relation is obtained and stability criterion is given in the terms of critical value of relative velocity. It has been observed that the inclusion of irrotational shearing stresses have stabilizing effect on the stability of the system.

In this study, surface tension modeling is developed using intermolecular thermodynamic potential function including the two-parameter Lennard-Jones model in a semi-analytical form and the three-parameter well-square model in a full-analytical form in a wide range of temperatures in the bulk scale. The comparison of the results for hydrocarbon fluids (light to heavy) and non-hydrocarbon fluids shows that the prediction of surface tension through the square-well model, due to its high flexibility and mathematical simplicity compared to the Lennard-Jones model, provides significant agreement with experimental data.

In hydrologic regional frequency analysis, information of one or more stations is generalized for a region. In this case, the variation of this information is assumed to have a defined coefficient called scale. In this study, scaling properties of 7-day low flow of 19 basins in Mazandaran province in northern Iran were investigated. Scaling implies the relationship between probabilistic features and the area of the basin. If this exponent (called scaling exponent) has a linear relationship with drainage area and does not include a significant relationship with probability weighted moments, low flow is called “simple scaling”. The study showed that the logarithm of the drainage area and the logarithm of the probability weighted moments of order 1 to 10 are linear and the scaling exponent did not have a significant relationship with probability weighted moments. Acordingly the 7-day low FLOWS of Mazandaran province are simple scaling.