Journal Of Applied Fluid Mechanics
Volume:9 Issue: 3, May-Jun 2016

In the oil & gas industry, the traditional procedure for slug catcher design is based on the Stoke's law. Design equations are obtained from a 1-D analysis and validated with experimental data. Therefore, this method basically relies on simplified models and empirical correlations. For this reason, an over margin factor from 20 to 40% is usually applied. In this paper, a simplified CFD procedure for the modelling of the gas-liquid separation is presented. Steady state and transient models have been considered for single phase and multiphase fluids, using OpenFOAM. The influence of flow model and mesh grid on results have been evaluated as a trade-off between solution accuracy and computational efforts, in order to assess the applicability of these models to industry. A comparison of the industrial validation procedure with the CFD analysis has been realized, focusing on the pros and cons of the two different approaches. A new application solver has been constructed and programmed in order to get the most accurate results with the minimum computational efforts. This solver is based on a completely new and innovative approach to the Navier-Stokes equations for multiphase flow. New model proposed has been used for the evaluation of design for the two slug catchers studied, in order to get a better separation and fluids management.

A 3D numerical simulation using large eddy simulation (LES) method is performed for a submerged turbulent water slot jet impinging normally on a flat plate with a nozzle-to-plate distance of 10 jet width and a Reynolds number of 16000 and the results are compared with the existing experimental data. The numerical platform is an open source CFD code based on the field operation and manipulation C class library for continuum mechanics (OpenFOAM) and is used to simulate the flow and represent the mean and instantaneous flow field characteristics. Also, simulations are performed with two different subgrid-scale (SGS) models, one-equation based subgrid-scale model and localized dynamic smagorinsky model. Evaluating the different subgrid-scale (SGS) models, a priori and a posteriori test is done. Comparison between results obtained using the SGS models and experimental data shows that the simulation results using localized dynamic Smagorinsky model are more compatible with the experimental data compared with those that obtained from the kinetic energy one-equation model especially in regions close to the impingement wall and in free jet region.

This paper presents a geometrical optimization of a heat sink modelled using three dimensional CFD. The heat sink studied is circular with radial inlets and parallel fins. The parameters of the optimization are the different spacings between the fins. The optimization process is multi-objective and uses an aggregated objective function of both the thermal resistance and the pressure drop of the system. To perform the optimization, a relatively new technique has been used called Variable Neighbourhood Search (VNS). The optimization results give several interesting new geometries. In addition, the performances of VNS are measured with two criteria: the speed of convergence and the repeatability between two optimization runs. These performances are good compared to more traditional optimization techniques like Genetic Algorithms.

Nowdays, we face important energy challenges. These ones are making scientist all over the world reconsider the way they look into problem and find innovative solutions to improve industrial processes efficiency. One of many original ideas is the use of “not-regular” fluids over regular applications. Aqueous Foam Flow present several unusual rheological properties when put inside a horizontal channel: low density, visco-elasto-plastic behaviour, and high wall shear stress. These ones give this type of fluid interesting capacities and uses: Assisted oil extraction, heat exchange, lubrication. In this study we undertake the causes of these interesting properties, which are directly related to the liquid slip-layer located between the flowing bubbles and the walls. For different velocities (2 cm/s, 4 cm/s and 6 cm/s) and void fractions (from 55% to 85%) we will study the influence of the liquid film thickness over the wall shear stress,using innovative measurement techniques: conductimetry and polarographic methods. An interesting relationship is seen between the limit diffusion current, required to accurately utilize the polarographic method, the wall shear stress and the liquid film thickness. The bubbles passage over the walls generates an oscillation of theslip-layer thickness which directly affects the polarographic results. However, as we increase the foams velocity this influence diminish and the wall shear stress calculations are more accurate.

In the present study, the hydrodynamic behaviours of the Couette Taylor flow in different flow regimes were investigated, experimentally and numerically.In this research, the effects of Taylor number on wavelength of the flow, which are two important hydrodynamic charactristics of the Couette Taylor flow, are investigated both experimentally and numerically in order to study the stability of the flow and formation of vortices. In addition, the velocity and pressure variation of the the flow between two cylinders were considered and compared for different Taylor numbers to understand the behaviuor of the flow.

The Taylor-Couette problem is a fundamental model in bifurcation theory and hydrodynamic stability. The inner cylinder rotation generates a flow pattern known by a transition to turbulence through a sequence of successive hydrodynamic instabilities. The effect of an imposed axial flow on the instabilities evolution is studied. An experimental device was designed to study this effect. It consists of two concentric cylinders with the inner one rotating and the outer one fixed, and a pressure driven axial flow can be superimposed in the annulus. In addition, various motion of the inner cylinder can also be imposed (oscillation, gradual or abrupt disturbance).The objectives are to investigate the effect of the superposition of an axial flow on the stability of the flow and its influence on the vortex behavior and hence on the wall shear stress. The resulting structure of the flow then depends on the initial flow regime, due to the rotation of the inner cylinder and the velocity of the axial flow. Consequently, two dimensionless parameters are defined to characterize the flows: the Taylor number and the Reynolds number of the axial flow. Experimental PIV measurements are devoted to characterize the Taylor-Couette flow dynamics with imposed axial flow and then synchronized with electrochemical measurements to study the vortex-wall interaction.

This paper presents a method to improve cylinder design of 2-stroke auto-ignition engine based on a CFD (Computational Fluid Dynamics) study of internal flows in the chamber and an unsteady global 0D parametric approach. In 2-stroke engine, scavenging process plays an important role regarding engine efficiency and pollutant emissions. Several geometrical and environmental parameters (like piston velocity and inlet/outlet thermofluid conditions) impact the scavenging process and most of them vary when the engine is running. To improve the scavenging process, an analytical model (integrating design parameter variations) is developed and will be implemented in 0D global model. CFD simulations are used to establish the analytical scavenging model. The CFD model includes species transportation, piston motion (remeshing), turbulent effectsbut it does not take into account the combustion process or the aerodynamics in the cylinder before the beginning of scavenging. After defining the influent parameters on the scavenging, multiple simulations with varying values of parameters were run and a data base was created. The data base will be used to develop a reduced model of the scavenging process which will be integrated in a global 0D model of the engine. Through a reference case, the in-cylinder flow is analyzed and the evolution of velocity, pressure, species and turbulent kinetic energy fields during scavenging are discussed. After a statistical treatment, the results of simulations highlight two main significant parameters: the advance of intake opening and the angle of the intake duct. The decoupling of these two parameters is particularly suitable for the optimization of engines.

This work investigates the influence of laser power on an evaporating single droplet made from an H2O and NaCl mixture. Heat and mass transfer of a single droplet with the presence of a low power laser source (as He-Ne laser) is studied both numerically and experimentally in this article. A new model is presented to simulate water droplet evaporation. The model is robust enough to be applied for various initial concentrations and conditions of the droplet, ambient conditions, and dissolved media properties. Moreover, laser energy is taken into consideration as a source term which is a function of the wave length of the source beam and refractive index of the droplet. Considering the involved parameters, the model is implemented in a MATLAB code and validated using experimental data obtained in this study on top of those already available in the literature. Experimental data were collected for droplets with an initial radius of 50 μm at room temperature for three initial concentrations of 3%, 5%, and 10% (by mass) of NaCl in water as well as pure water droplet to provide a comprehensive validation dataset. It is shown that low-power laser source significantly increases the evaporation rate (2.7 to 5.64 for 0% and 10% initial concentration of salt, respectively) which must be taken into consideration while using laser based measurement techniques.

The present study aims to reduce the computational cost of in-cylinder phenomena simulation under the light of employing Proper Orthogonal Decomposition (POD) technique. The equivalence ratio as the main identifier for soot formation tendency along with temperature and nitrogen oxide fields, are studied inside a gas-fuelled engine. The required correlation matrix is built based on ten snapshots obtained from the results of engine three-dimensional simulation, which are verified based on experimental data. The AVL-FIRE v.2013 software is used to carry out the three dimensional simulations. The flow field at 3250 rpm is then estimated by POD coefficients and subsequent curve fittings. To validate the reduced order results, this condition is simulated by the software. For instance, temperature and equivalence ratio fields at top dead center and 5 degree after top dead center are compared. The relevance index for equivalence ratio indicates about 96% consistency between reduced order and 3D simulation results. On the other hand, this index is found to be about 99% at both crank angels for temperature, which proves a more coherent structure in the temperature field than that of equivalence ratio. Meanwhile, the analysis of 3D simulation results by POD demonstrates a more coherent structure for the in-cylinder flow regime at top dead center. This consistency is obtained in spite of computation time of POD being approximately 1% of 3D simulation time.

In carbon capture and storage system, the captured COR2 from energy production processes is compressed to high pressures, transported to a storage site, and then injected into a suitable geologic formation. The leakages from high pressure transportation pipelines would pose hazard to the environment and people. In this paper, a laboratory scale rig for simulating COR2 pipeline leakage is built, and a two-dimensional model is further developed to study the complex behavior of the jet and dispersion of COR2 from the rig at continuous leakage flowrate. In view of the phase-change heat transfer of COR2, a multiphase flow model is used to simulate thejet and dispersion of COR2 gas-liquid two-phase flow. The Euler/Lagrange model and particle stochastic trajectory model are applied to describing the development process of the jet and dispersion of COR2. The computational fluid dynamics software Fluent is employed to calculate the flow field. To prove the validity of the numerical models, an infrared thermography is used to record the temperature field near the leakage orifice during experiments.

In this study aerodynamics analysis of full scaled Vestas V47 wind turbine is carried out by the use of modified blade element momentum (BEM) theory and computational fluid dynamics (CFD). In order to determine accurate results BEM theory is programmed by considering drag coefficient, Glauert correction and Prandtle tip loss factor. CFD simulation is determined employing k-w sst turbulence model and periodicboundary condition. The investigation outcomes are compared with each other. To validate CFD and BEM results, the only available data is real field measurement that is done by Vestas Company and power is compared with these data. Finally, according to the accuracy of results and computational cost, it is obtained that BEM is more applicable in engineering estimations.

In this paper, we realized an Experimental study of heat and mass transfer for liquid evaporation along a vertical plate covered with a porous layer. To develop this study, an experimental dispositive was realized. To highlight the effect of the addition of a porous layer on the phenomenon of evaporation, we first study the case of the flow of a liquid film on an aluminium plate. Then we covered the same plate by a porous layer. We could measure the temperature along the plate and the evaporated flow using the test bed. From these measurements we note that temperatures are higher with the presence of the porous medium which affect positively on the evaporated flow. In addition, various dimensionless numbers were analyzed as the sensible and latent local Nusselt number, solving the energy equation by inverse method. We note that the latent Nusselt number is more important than the sensible Nusselt Number. Then the flow dissipated by evaporation is greater than that used by the film to increase its temperature. We also note that the calculated values of the latent and sensible Nusselt number are greater in the presence of the porous medium that proves that the addition of the porous layer improves heat and mass exchange.

In explosion-structure interaction problems, an accurate prediction of blast loading remains a hard challenge. The reflected overpressures around a complex structure, such as a building with an apse and an atrium are almost always unpredictable so that experiments and numerical simulations may be the only possibilities to evaluate the threat of an industrial explosion. Well instrumented blast experimental studies are first carried out at small scale on a rigid specimen with a variable incidence angle. The main objective is to observe and quantify the regular and irregular reflections and the diffractions of a blast wave on a real structure. In parallel, numerical simulations are performed with a home-made eulerian CFD code. The comparison with experimental results permits to discuss the capabilities and limitations of numerical blast predictions.

Transition to turbulence of a viscous incompressible fluid flow between two concentric spheres with the inner one rotating and the outer stationary was investigated experimentally. The flow modes were studied using the flow visualization and electrochemical technique. Different flow states were obtained for the gap/radius ratio 0.107 in function of the Taylor number in the interval (22 - 1500) and aspect ratio (17 - 21). Observed states were classified into: Taylor Vortex Flow (TVF), Spiral Mode (SM), Spiral Mode & Wavy Mode (SM), Spiral Wavy Mode (SWM), Wavy Mode (WM) and Chaos. The variations of the flow patterns were reflected by the wall velocity gradient, its fluctuation and spectral analysis. Fast Fourier transform applied on the time series of the wall velocity gradient allowed for the analysis and identification of the fundamental frequencies and their evolutions associated with each flow state.

In this work, a numerical study of forced convection of an incompressible fluid through a cylinder filled with a porous medium is carried out by taking into account the heat due to viscous dissipation. Dimensionless equations of the problem are solved numerically. The energy transport bidimensional model is based on the local non-thermal equilibrium assumption with consideration of viscous dissipation effects. The influence of various parameters like Darcy number, Reynolds number, Forchhheimer coefficient and Eckert number on temperature fields is investigated and examined throughout this paper. It is found that all these parameters have significant influence on thermal performance of the packed bed within certain conditions.

In the simplest and original case of study of the Taylor–Couette TC problems, the fluid is contained between a fixed outer cylinder and a concentric inner cylinder which rotates at constant angular velocity. Much of the works done has been concerned on steady rotating cylinder(s) i.e. rotating cylinders with constant velocity and the various transitions that take place as the cylinder(s) velocity (ies) is (are) steadily increased. On this work, we concentrated our attention in the case in which the inner cylinder velocity is not constant, but oscillates harmonically (in time) clockwise and counter-clockwise while the outer cylinder is maintained fixed. Our aim is to attempt to answer the question if the modulation makes the flow more or less stable with respect to the vortices apparition than in the steady case and if there are any reversing or non reversing flows apparition. If the modulation amplitude is large enough to destabilize the circular Couette flow, two classes of axisymmetric Taylor vortex flow are possible: reversing Taylor Vortex Flow (RTVF) and Non-Reversing Taylor Vortex Flow (NRTVF). Our work presents an experimental investigation of the effect of oscillatory Couette-Taylor flow on the instantaneous and local mass transfer and wall shear rates evolutions, i.e. the impact of vortices at wall; and the detection of any RTVF and/or NRTVF apparition. The vortices may manifest themselves by the presence of timeoscillations of mass transfer and wall shear rates; this generally corresponds to an instability apparition even for steady rotating cylinder. On laminar CT flow, the time-evolution of wall shear rate is linear. It can be presented as a linear function of the angular velocity. For a mean Taylor number corresponding to a laminar Couette flow, a modulation frequency F = 0.1 Hz and an amplitude respectively β = 0.53 andβ = 1.08 are sufficient to destabilize the laminar CT flow, Taylor vortices appear. Comparing to a steady rotational velocity case, oscillatory flow accelerates the instability apparition, i.e. the mean critical Taylor number corresponds to the transition is smaller than that of the steady rotational case. The vortices direction can be deduced from the sign of the instantaneous wall shear rate time evolution.

In this work, we investigated experimentally the hydrodynamics of flows crossing conical diffusers. On our previous work (Aloui et al. 2011) CFD turbulent models were validated for flows crossing the critical angle (2=16°). Indeed, the PIV data base constructed was exploited to validate a variant of SST-RLC model. Taking into account the conical diffuser angle effect, the apparition and the development of vortices were observed and studied. The dynamics of the recirculation zones which may be observed at the lower and higher parts of the singularity, has not formed the subject of numerous studies. There were no studies that characterize the vortices at the conical diffusers in terms of size, centre positions, and vortex intensity. Consequently, two conical diffusers were studied using the Particle Image Velocimetry technique (PIV). The results illustrate effects of “opening angle” (2=16°) and (2=30°) on the flow structures developed in such type of diffusers. From such opening angle of conical diffusers, the progressive angle increasing generates a detachment of the boundary layer of the conical diffuser depending on the turbulence level. This detachment may lead to a coherent flow structures. We applied the coherent structures criterion G2 to the recorded velocity fields to detect and characterize the vortices at the conical diffusers. We used the Proper Orthogonal Decomposition (POD) to filter the PIV data base constructed and to extract the most energetic modes. The results illustrate that the turbulent flow structures can be constituted using a limited number of energetic modes.

In this investigation, effects of dispersed Cu nanoparticles in water on heat transfer coefficients are studied using Eulerian-Lagranigian approach. Nanoparticles disperse in the fluid due to drag, weight and Brownian forces acting on them. A new particle search algorithm is used to trace the particles in every time step. Thermal coupling between dispersed and carrier phases is done and also thermal and momentum interaction between particles and solid walls are taken onto account to obtain velocity and temperature fields. The specific heat of nanofluid is obtained using conventional models. The results show that regarding thermophysical properties of particles and base fluid, and also other conditions like mass flow rate and particle size, degradation or intensification of heat transfer coefficients can occur.

Acoustic streaming, as an important phenomenon, is used in a wide variety of applications such as drug delivery and the removal of plaque in the vein surfaces. The purpose of the current paper is to investigate the effect of blood, as a non-Newtonian fluid, on acoustic streaming. The governing non linear differential equations, mass, momentum, and state equations for non-stationary fluid using second-order perturbationtheory, are coupled and solved. An in house computational fluid dynamics (CFD) code based on the finite element method is utilized. Results show that viscosity is highly dependent on shear stresses, about 60%. In addition viscosity affects the acoustic streaming velocity field.