Amina Radhouane

Impact of the Temperature of Twin Inclined Tandem Jets on Their Dynamic Interaction With a Cooler Oncoming Crossflow

We deal in the present paper with the commonly known “jets in crossflow” configuration. The interest raised by this configuration comes from its wide application in several fields and from its dependence on numerous parameters. Its well understanding is crucial in the way it helps solve problems in relation with the mixing processes, the heating and cooling performances, the control of fume dispersion, etc... These problems are also faced in small-scale applications like electronic devices cooling or the pulverization of fuel in combustion chambers through infinitely small nozzles, etc... The jets handled in our study are elliptic, aligned in the same direction of the oncoming crossflow, undergoing the same initial conditions and their dimensions are within the micro-scale. In addition to these primer conditions, an injection ratio of R=2 is imposed between the velocities of the jets and the main flow. The jet nozzles adopt a streamwise inclination of 60° and are separated with a distance of three diameters (the little ellipse diameter). The configuration is examined both experimentally by means of the Particle Imagery Velocity (PIV) technique and numerically with the finite volume method. The latter is based on the resolution of the Navier Stokes equations by means of the RSM second order turbulent closure model and a non uniform mesh system that is particularly refined near the injection nozzles. Once validated by confrontation to the experimental data, our numerical model will be generalized by the introduction of further conditions that make it more realistic. A non reactive fume is injected within the jets and a variable temperature gradient is imposed between the jets and the crossflow. Our aim is precisely to evaluate the impact of the introduced temperature gradient on the reigning flow field, and particularly on its dynamic features (the different velocity components).Copyright

Dispersion of Twin Inclined Fume Jets of a Variable Height within a CrossFlow

Twin elliptic inclined tandem jets are emitted within an oncoming cooler crossflow. The jets contain a non reactive fume whose dispersion is tracked all over the surrounding domain. Such a configuration may be found in chimney stacks, ships’ chimneys, etc. We propose to evaluate in the present paper the impact of the jets’ height on the resulting dispersion process. To reach this goal, a numerical simulation of a double jet model of variable height is carried out by means of the finite volume method together with a non uniform grid system. The model, validated by previous experimental data, allowed the tracking of the emitted fume by studying the evolution of a single particle contained within this fume, the Carbone dioxide (CO2) mass fraction. This is possible thanks to the assumption of handling a non reactive fume, which is adopted only to simplify the calculations. The CO2 mass fraction was mainly tracked between the emitting nozzles, in a try to find out the changes brought by the extension of the emitting jet nozzles on the flow trapped between them.

Assessment of a Chimney Jet Flowing Around an Obstacle

A numerical modeling study was undertaken in order to examine the structure of the flow issued from a bent chimney around a parallelepiped obstacle. The main purpose of this work is to track the overall evolution of the flow and determine the thermal and mass transfer features that characterize the resulting flow field. We first validated the numerical model with experimental data. The experimental data are depicted by means of a particle image velocimetry technique. The numerical model is simulated by solving the mass, momentum, energy, and species equations. The finite-volume method is used, together with the second-order Reynolds stress model. A good level of agreement was achieved between the experimental data and numerical calculations. The comparison concerned both the mean and fluctuating dynamic features. Once validated, our model allowed the evaluation of the effect of different parameters on the heat and mass transfer features. These parameters consist of the velocity ratio (0.5, 1, and 1.6), the distance separating the chimney and the obstacle (100 mm and 200 mm), the height of the obstacle (50 mm, 90 mm, and 150 mm) and the orientation of the bent chimney (15°, 30°, and 45°). The evaluation of the effects of these different parameters has the ultimate purpose of determining the optimum conditions for the weakest concentration of pollutants.

Dispersion of Twin Inclined Fume Jets of Variable Temperature within a Crossflow

This paper deals with the interaction of twin elliptic jets with a cooler oncoming crossflow. The jet nozzles are placed tandem with the main flows, three diameters one from another and initially inclined with a 60° angle. The exploration of the resulting flowfield was carried out numerically by means of the finite volume method together with the RSM (Reynolds Stress Model) second order turbulent closure model and non uniform grid system that was particularly refined near the nozzles. After validation with reference to PIV (particle image velocimetry) experimental data, the model was upgraded by discharging a non reactive fume from the jet nozzles and introducing a variable temperature gradient between the interacting flows. We focused mainly in the present work on the determinant role of the temperature gradient on the dispersion of the discharged pollutants within the domain. Such a study is likely to optimize (control, reduce, eliminate, etc.) one of the most alarming nowadays’ environmental concern: the atmospheric pollution.

Thermal Field of Twin Variably Elevated Tandem Jets in Crossflow

Consideration is given to twin inline elliptical fume jets issuing within an oncoming cooler environmental crossflow. Jets are emitted from similar nozzles, characterized by a variable injection height. Such a configuration is found at large scale, in the industrial urban zones, and more particularly in multiple chimney power plants. It is found at small scale as well like in cooling in electronic devices. The present study is carried out numerically by means of the finite volume method together with the Reynolds Stress Model (RSM) second order turbulent closure model and non uniform grid system particularly refined around the emitting nozzles. Emphasis is put on the temperature distribution around the emitting nozzles in order to highlight the joint effect of the jets elevation and temperature. It was mainly found that both parameters are complementary and help straitening the discharged jets, leading their thermal mixing away from the injection ground. Nomenclature

HEAT TRANSFER GENERATED BY THE INTERACTION OF SINGLE AND MULTIPLE TANDEM JETS IN CROSSFLOW

“Twin jets in Crossflow” is a common configuration that finds application in several large and/or small scale industrial fields. The interest in such a configuration is further enhanced by its dependence in several parameters, that may be geometric, dynamic, thermal, or relative to the handled fluid composition. We propose to focus in the present work on the effect of the number of the emitted jets on the generated heat transfer, in presence of an unchanged uniform crossflow. To reach this goal, single, double and triple jet configurations were simulated, based upon the resolution of the Navier Stokes equations by means of the RSM (Reynolds Stress Model) second order turbulent closure model, together with a non uniform grid system particularly tightened near the emitting nozzles. After validation, we tried to find out the impact of the number of the handled jets on their cooling “power” by tracking the temperature distribution of the resulting flowfield. Since in practically all applications we are in need of higher efficiencies and then of higher operating temperatures, we are constantly concerned about not going beyond the shielding material melting temperature. If the use of cooling jets proves to be efficient, this may bring a significant progress in the technological field. Keywords: twin jets, crossflow, jets‟ number, heat transfer.

Dynamic and Thermal Evolution of Twin Inclined Jets Among a Cool Crossflow: Jets’ Inclination Impact

This paper treats the complex and very interesting “twin inclined jets in crossflow” configuration. The complexity of the problem originates from the double interaction occurring between the jets on one hand and between the jets and the crossflow on the other hand. The interest of the configuration is essentially due to its presence in more than an application (VSTOL aircrafts, chimney stacks, etc..) and in more than a field (industrial, academic, etc..). For the matter an experimental study and a numerical simulation were conducted. The experiments were carried out in a wind tunnel. The results were tracked by means of the PIV technique. That could provide us with the velocity and the turbulence cartographies. The numerical processing was based upon the resolution of the Navier-Stokes equations by means of two different turbulent models: the standard k-e model and the RSM (Reynolds Stress Model) second order turbulent model. The confrontation of their corresponding results together with the experimental data decided on the better efficiency of the RSM model to represent well the different processes occurring within the resulting flowfield. After that, a non uniform grid particularly tightened near the injection nozzles was adopted. Once the validation reached, we could generalize our study to introduce a non reacting fume through the twin jet nozzles and to test the impact of two major factors on the mixing process; we want to mean the initial transverse inclination of the injection nozzles.Copyright

Twin Inclined Circular Jets Evolution Through a Cool Crossflow

The aim of this paper is to examine experimentally as well as numerically the flowfield resulting from the interaction between a twin circular inclined hot jets emerging into a cooling crossflow. The resulting flowfield is quite complex due to the presence of different vortical structures including the kidney vortex, the horse-shoe vortex, etc... The evolution of the twin inclined jets through the crossflow could be depicted by tracking the mean-flow velocity field and its associated turbulence statistics by means of the PIV technique. This evolution can be influenced by many factors. Herein, we will deal with that resulted by the injection nozzles’ inclination and the jets’ spacing. Then, we performed a three dimensional sample of the studied configuration in order to simulate the evolution of the resulting flowfield. For that, the Navier Stokes equations were simulated with an RSM second order turbulent closure model. Then a non uniform meshing was applied. A good agreement was obtained between the experimental data and the numerical modeling. After validation we could represent in addition to the available results, the temperature distribution and the effects the variation of the injection inclination and that of the jets’ spacing bring on it (on its spatial evolution).Copyright