Key words: Compressible turbulence, Pressure-strain correlation, Homogeneous shear flow .

Abstract: Several DNS results show that compressibility has an important effect on the pressure-strain correlation, the termrecognized as the principal responsible for the change in the magnitude of Reynolds-stress anisotropies. Thus, the pressure-strainincompressible models do not correctly predict compressible turbulence at high-speed shear flow. A method of includingcompressibility effects in the pressure strain correlation is the subject of the present study. The LRR model developed byLaunder-Reece and Rodi has shown a great success in the simulating a variety of incompressible complex turbulent flows. On theother hand this model has not predicted correctly the compressible turbulence at high speed shear flow. Thus, a compressiblecorrection for this model is the major aim of this study. In the present work, five recent compressible models for the pressure-straincorrelation have been used to modify the LRR model. This correction concerns essentially the C1, C2, C3 and C4 coefficients which became in a compressible situation a function of the turbulent Mach number.

Key words: Water Hammer, Leak detection, Elastic pipe, viscoelastic pipe, Transient pressure.

Abstract: This paper further investigates leaks detection in elastic and viscoelastic pipes based on the analysis of water hammer wave. Leak as an internal exciter and a discontinuity that occurs in a hydraulic system may affect the waveform. Its effects on the pressure wave at the end section of a reservoir-pipe-valve system can be used as a tool for its location and sizing. The leak modeled as an orifice is located in the studied system either with elastic or viscoelastic behavior. Its location is given by analyzing the head pressure at the valve either in the time or the frequency domain. The effect of the pipe-wall elasticity (instantaneous elastic response) and viscoelasticity (retarded –viscoelastic response) on the leak detection are investigated either in time or frequency domain. Finally a comparison between the two analyses for leak detection is drawn.

Key words: Binding reaction, microfluidic systems, biosensors, finite element method, biological analytes, simulation.

Abstract: The binding reaction is a significant characteristic which is adopted in the design of biosensors. This aim of the present work is to investigate the binding reaction kinetics through a microchannel. The  diffusion boundary layer on the reaction surface of a biosensor operating in fluid environment, presents restraining effects. Therefore, it is useful to optimize several critical parameters, which affect the binding reaction such as, the length of the reaction surface, the inlet flow velocity, and the initial biological analyte concentration (e.g. molecule, protein, toxin, peptide, vitamin, sugar, metal ion…) in order to reduce the thickness of the diffusion
boundary layer. The study is performed using 2D finite element method. Then, the space-time evolution of analyte concentration (such as C-reactive protein or IgG) is simulated. The results prove that the reaction kinetic is strongly affected and hence the diffusion boundary layer is assigned by the physical and geometrical parameters of the microfluidic biosensor.

Keywords: Lattice Boltzmann method, multiphase flow simulation, Darcy law, porous media, kinematic viscosity.

Abstract: In this paper, we present a Lattice Boltzmann simulation of multiphase flow in a homogeneous two-dimensional porous media. For this study, we develop a program based on lattice Boltzmann equation. The underlying theoretical model makes it possible to couple the state equation of a non-ideal fluid with the pressure tensor at the interface and uses the excess free-energy density formalism. The fluid properties can be  prescribed in a thermodynamically consistent manner, which remains accurate at states close to the critical point. We have simulated some known two-phase flow configurations, like displacement of vapor by its liquid in homogeneous two-dimensional porous media reconstructed by image treatment under the action of an external flow field. We present also results for the averaged velocity as a function of time iteration and the permeability of two dimensional porous media as a function of kinematic viscosity and mesh resolution. Our results confirm that the LBM scheme reproduces Darcy’s law through the analysis of the dependency of the permeability on the kinematic viscosity.

Key words: Nanofluid, Natural convection, Heat transfer, Solid volume fraction.

Abstract: This paper analyzes heat transfer and fluid flow of natural convection in an inclined cavity filled with CuO/water nanofluid that operates under differentially heated walls. The transport equations for the flow are solved numerically by the finite volume element method using the SIMPLER algorithm. Simulations are performed for various aspect ratios. The inclination angle is varied between 0 and 90°, and the Rayleigh number is in the range of 103 and 105. Temperature distribution and heat transfer rates are analyzed and discussed. It is found that the addition of solid nanoparticles in working fluid lead to a considerable enhancement of heat transfer. Effects of aspect ratio, inclination angle, and Rayleigh number on heat transfer are analyzed.