Philippe Bournot

Three-Dimensional Numerical Calculations of a Jet in an External Cross Flow: Application to Pollutant Dispersion

We present a three-dimensional numerical simulation of a circular turbulent jet issuing transversely into a uniform air stream. In the first part an air-helium jet is considered and the three-dimensional structure of the flow field is discussed. Then, a comparison between the numerical results of four turbulence closure models (three first-order models and a second-order one) are presented and compared with the experimental data given by Crabb et al. , and Andreopoulos et al.

Influence des conditions d'émission sur un écoulement de type jet plan laminaire isotherme ou chauffé

Abstract We propose numerical solutions for a laminar jet, accounting for emission conditions at the exit of the nozzle. Two emission cases are considered in this study: velocity and temperature profiles are uniform or parabolic, respectively. A finite difference scheme is developed for the resolution of the equations governing the isothermal and non-isothermal free jet and wall jet developing tangentially along an adiabatic flat plate. The analysed results are the centerline velocity and centerline temperature for the free jet, and wall temperature and shear stress for the wall jet. The results obtained are compared to another method that is based on two constraints of integration, i) conservation of momentum and ii) conservation of energy, to replace the emission conditions at the exit of the nozzle for the resolution of equations. Our results of the velocity and temperature profiles compare well with those obtained by the latter method solely in the plume region, where buoyancy forces are responsible for flow.

Étude numérique des conditions d'émission sur un écoulement de type jet plan turbulent isotherme ou chauffé

Abstract We intend to solve equations governing turbulent plane-vertical isotherm and non isotherm jets by taking into account inflow conditions at the exit of the nozzle. The analysis is focused on the influence of these conditions on this type of flow. Two cases are considered (uniform and parabolic velocity and temperature profiles). A finite difference scheme is developed to solve the governing equations. This numeric model allows us to show that the region of fully developed regime begins much nearer the nozzle for the turbulent case than for the laminar flow case. Indeed, the turbulence increases the mixing between the incoming gas from the nozzle and the ambient fluid, and consequently the size of the potential core zone decreases. The results are compared to other works introducing mathematical variables based on the energy conservation for the case of the mixed convection and the momentum conservation for the forced convection, which allows the validation of our results.

Numerical Study and Optimization of Parabolic Trough Solar Collector Receiver Tube

In this study, the parabolic trough collectors (PTC) performance is analyzed. In order to achieve this goal, the adopted procedure comprises two main steps. In the first step, the concentrated solar heat flux densities in the solar concentrator focal zone are calculated by soltrace software. In the second step, computational fluid dynamics (CFD) simulations are carried out to analyze and to optimize the thermal performance of the tube receiver. The calculated heat flux densities by soltrace software are used as wall heat flux boundary conditions for the receiver tube. The effect of the receiver tube diameter variation on the PTC thermal performance is studied. A new type of receiver tube is tested. This latter is covered with a metallic thickness. The performance of tube receiver covered with a metallic layer for different diameters is compared to those of the same diameters without the addition of metallic thickness. It has been found that increasing tube metallic thickness enhances the performance of PTC system comparing to the tubes of the same diameter and crossed by the same flow rates.

NUMERICAL STUDY OF A HEATED PULSED AXISYMMETRIC JET IN LAMINAR MODE

In this work, we have studied numerically the influence of a pulsation on the flow generated by an axisymmetric immerged jet in a laminar mode. A finite-difference method is used to solve the dimensionless equations governing the flow. The simulation enabled us to determine the space-time evolution of the flow variables, such as the velocity components, temperatures, length of the potential core, and both the dynamic and thermal half-thicknesses. The results obtained are the outcome of various factors such as the pulsation amplitude, the frequency which affects the Strouhal number value, and the Reynolds and the Grashof numbers. All of them show that a pulsed jet reaches an asymptotic mode identical to that of the steady one. On the other hand, the pulsation considerably accelerates the expansion of the jet and clearly improves the entrainment at the nozzle exit for distances of some diameters. The results reached in this work are validated with those obtained for a steady jet in its various aspects.

Numerical study of the thermal and aerodynamic insulation of a cavity with a vertical downstream air jet

Abstract This work is devoted to a numerical approach of the laminar mixed convection in a cavity which one of the boundaries is materialized by a laminar vertical downstream air jet. The purpose is to analyze the interaction of this flow with the natural movement that grows in the cavity under the combined action of boundary thermal gradients and external medium of the cavity in order to examine thermal insulation qualities of the jet. Calculations have been made with the help of the finite volume method.

Numerical study of a heated cavity insulated by a horizontal laminar jet

Abstract In this work, we present a numerical study of the thermal insulation of a heated two dimensional cavity limited on its superior part by a horizontal plane air jet. The lower horizontal wall is isothermal, while the two vertical walls are adiabatics. A finite difference method based on the stream function–vorticity formulation is developed to solve the dimensionless Navier–Stokes and energy equations resulting from some assumptions. The results allowed us to point out two flow configurations: if natural convection prevails, the hot jet issuing from the nozzle diffuses upwards, and consequently, the cavity cannot be insulated correctly. However, the use of an aspiration zone can then improve the insulation. When forced convection predominates, the hydrodynamic barrier is conserved, and the enclosure is also thermally well confined.

Distribution characteristics of pollutant transport in a turbulent two-phase flow

The distribution characteristics of pollutants released at varied rates and different vertical inlet positions of an open channel are investigated via a three-dimensional numerical model. Pollutants are injected from time-dependent sources in a turbulent free-surface flow. Numerical computations were carried out using Fluent 6.3, which is based on the finite volume approach. The air/water interface was modeled with the volume of fluid method (VOF). By focusing on investigating the influences of the flow on pollutants, it is found that with an increase of the injection rate, the pollutant concentration increases along the channel and the longitudinal dispersion is higher. On the other hand, it is noted that the point of injection modifies significantly the dispersion pattern of pollutant. These findings may be of great help in cost-effective scientific countermeasures to be taken into account for accident or planned pollutants discharged into a river.

Prediction of pollutant dispersion in turbulent two-phase flows

With a growing awareness of water pollution problems, in recent years there has been a considerable increased effort in developing and applying numerical models to predict accurately the contaminant distributions, particularly in free surface flows. This numerical study presents a predictive hydrodynamic model in order to explore the dispersion phenomenon of a pollutant injected from time-dependent sources in a turbulent free surface flow. More precisely, we study the impact of pulsation on the dispersion of an injected material. The air/water interface was modeled with the volume of fluid method and sharpness of the free surface was assured by means of Geo-Reconstruct scheme. The numerical results showed that the pulsation played a dominant role at the early stage of the pollutant transport. It was also observed that the pulsation affected the distribution of the injected material especially near the front and that a major swirling action was developed compared to the constant-rate-injection case.

Performance Optimization of Water-Cooled Concentrated Photovoltaic System

In this paper, a three-dimensional computational fluid dynamics model is developed to predict the thermal and electrical performance of a water-cooled concentrated photovoltaic (CPV) system. Based on the good agreement between the numerical results and experimental data from literature, an attempt was made to improve this system performance. Indeed, as the developed model is able to predict the thermal behavior of the different system components, many hot spots were detected in the cell module. In order to avoid this disadvantage while promoting solar cell cooling, the number of water cooling pipes of the CPV module was first increased and then a rectangular channel was employed. Numerical simulation results indicate the potential of the different modified systems for reducing these hot spots and the CPV module temperature, thus providing increased electrical and thermal efficiencies. The optimum design, which presents a solar cell temperature of 315.15 K and respectively a thermal and combined (thermal plus electrical) efficiency of 74.2% and 83.5%, is also evaluated.