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.

The corrections for log law must be taken into account the presence of bubbles in the two phase TURBULENT boundary layer. In the present study, a logarithmic law for the wall based on the supposition of additional TURBULENT viscosity associated with bubble wakes in the boundary layer was proposed for bubbly flows. An empirical constant accounting both for shear induced turbulence interaction and for non-linearity of bubble was determined for the new wall law, this constant was deduced from experimental measurements. In the case of a TURBULENT boundary layer with millimetric bubbles developing on a vertical flat plate, the wall friction prediction achieved with the wall law was compared to the experiences. We obtained a good concordance between experimental and numerical result. This significant agreement for wall friction prediction was particularly important for the low void fraction when bubble induced turbulence have a considerable role.

The objective of this paper is to examine the effectiveness of wall oscillation as a control scheme of drag reduction. Two flow configurations are considered: constant flow rate and constant mean pressure gradient. The Navier-Stokes equations are solved using Fourier-Chebyshev spectral methods and the oscillation in sinusoidal form is enforced on the walls through boundary conditions for the spanwise and streamwise (for the case of inclination cycle) velocity components. Results include the effects of oscillation frequency, amplitude, oscillation orientation, and peak wall speed on drag reduction at a Reynolds number of 180 based on wall-shear velocity and channel half-width as well as the Reynolds number dependency in both flow configurations. Drag reduction as a function of peak wall speed is compared with both experimental and numerical data and the agreement is good in the trend and in the quantity. Comparison between these two flow configurations in the transient response to the sudden start of wall oscillation, turbulence statistics, and instantaneous flow fields is detailed and differences are clearly shown. This analysis and comparison have allowed some light to be shed on the way that oscillations interact with wall turbulence.

Experimental investigations have been conducted on the two types of mixing layers produced from two streams merging at 0˚ and 20˚. Each type of mixing layers was produced with velocity ratios of 0.7, 0.8 and 0.9, and measurements were done at six streamwise locations. The boundary layers were untripped and the initial boundary layers were TURBULENT in all the cases. The results show that the splitter wake play a dominant role in the development of the mixing layers. Both types of mixing layers attained self-similarity for velocity ratios of 0.7 and 0.8, but failed for 0.9 within the measurement domain. With the increasing velocity ratio, development distance was increased and growth was decreased for both types of mixing layers, but the mixing layers with non-zero merging angles have higher growth than the zero angle one for the same velocity ratio. Both types of mixing layers were found to spread more and more into the high speed region with the increasing velocity ratio.