Modeling and numerical study of H2/N2 jet flame in vitiated co-flow using Eulerian PDF transport approach

2018 ◽  
Vol 19 (5) ◽  
pp. 504
Author(s):  
Ahmed Amine Larbi ◽  
Abdelhamid Bounif ◽  
Mohamed Bouzit
Keyword(s):  
Parametric Study ◽  
Numerical Study ◽  
Delta Function ◽  
Flame Stabilization ◽  
Model Accuracy ◽  
Ansys Fluent ◽  
Jet Flame ◽  
Eulerian Approach ◽  
Lift Off ◽  
The Impact

The multi-environment Eulerian approach (MEPDF) is the eulerian method to solve the PDF transport equations; it is considered a product of the delta function. Its advantages are the prediction of extinction and ignition of the flame, also the kinetic control of the species as CO and NOX. Even though the MEPDF approach has been improved in recent years, most improvements have been achieved with parametric study in order to investigate the impact of the model accuracy. The main objective of this work is to improve further the model accuracy, the prediction of the lift off height by a parametric study of the mixing constant and Schmidt number and to understand its impact in flame stabilization. The numerical investigation of H2/N2 jet flame in vitiated co-flow is presented using MEPDF approach. The study was applied with K-epsilon modified model of turbulence. The chosen mixture model is the IEM (Interaction by Exchange with the Mean). The number of environment in the multi-environment Eulerian approach MEPDF is (2.0). The model was solved in this work by the commercial CFD code, ANSYS fluent and the chemical reaction mechanism injected is GRI mech 2.1. The results are validated with experimental data and discussed.

Effects of Hydrogen Enrichment on the Reattachment and Hysteresis of Lifted Methane Flames

2013 ◽  
Author(s):  
James D. Kribs ◽  
Andrew R. Hutchins ◽  
William A. Reach ◽  
Tamir S. Hasan ◽  
Kevin M. Lyons
Keyword(s):  
Burning Velocity ◽  
Flame Structure ◽  
Flame Stabilization ◽  
Dominant Factor ◽  
Jet Flame ◽  
Lifted Flames ◽  
Methane Flames ◽  
Hydrogen Enrichment ◽  
The Stability ◽  
The Impact

The purpose of this study is to observe the effects of hydrogen enrichment on the stability of lifted, partially premixed, methane flames. Due to the relatively large burning velocity of hydrogen-air flames when compared to that of typical hydrocarbon-air flames, hydrogen enriched hydrocarbon flames are able to create stable lifted flames at higher velocities. In order to assess the impact of hydrogen enrichment, a selection of studies in lifted and attached flames were initiated. Experiments were performed that focused on the amount of hydrogen needed to reattach a stable, lifted methane jet flame above the nozzle. Although high fuel velocities strain the flame and cause it to stabilize away from the nozzle, the high burning velocity of hydrogen is clearly a dominant factor, where as the lifted position of the flame increased, the amount of hydrogen needed to reattach the flame increased at the same rate. In addition, it was observed that as the amount of hydrogen in the central jet increased, the change in flame liftoff height increased and hysteresis became more pronounced. It was found that the hysteresis regime, where the flame could either be stabilized at the nozzle or in air, shifted considerably due to the presence of a small amount of hydrogen in the fuel stream. The effects of the hydrogen enrichment, however small the amount of hydrogen compared to the overall jet velocity, was the major factor in the flame stabilization, even showing discernible effects on the flame structure.

scholarly journals Control of a Lifted H2/N2 Flame by Axial and Flapping Forcing: A Numerical Study

2021 ◽  
Author(s):  
Artur Tyliszczak ◽  
Agnieszka Wawrzak
Keyword(s):  
Numerical Study ◽  
Temperature Fluctuations ◽  
Mixing Process ◽  
Stochastic Field ◽  
Field Approach ◽  
Eddy Simulation ◽  
Fuel Jet ◽  
Large Eddy ◽  
Lift Off ◽  
The Impact

Abstract The large eddy simulation (LES) method combined with the Eulerian stochastic field approach has been used to study excited lifted hydrogen flames in a stream of hot co-flow air in a configuration closely corresponding to the so-called Cabra flame. The excitation is obtained by adding to an inlet velocity profile three types of forcing ((i) axial; (ii) flapping; (iii) combination of both) with amplitude of 15% of the fuel jet velocity and frequency corresponding to the Strouhal numbers St=0.30, 0.45, 0.60 and 0.75. It is shown that such a type of forcing significantly changes the lift-off height Lh of the flame and its global shape, resulting in a flame occupying large volume or the flame, which downstream the nozzle transforms from the circular one into a quasi-planar flame. Both the Lh and their spreading angles of the flames were found to be a function of the type of the forcing and its frequency. The minimum value of Lh has been found for the case with the combination of axial and flapping forcing at the frequency close to the preferred one in the unexcited configuration. The impact of the flapping forcing manifested through a widening of the flame in the flapping direction. It was shown that the excitation can significantly increase the level of the velocity and temperature fluctuations intensifying the mixing process. The computational results are validated based on the solutions obtained for a non-excited flame for which experimental data are available.

Numerical and Experimental Study on Lift-Off Suppression Phenomenon of Subsonic Hydrogen Jet Diffusion Flame

2010 ◽  
Author(s):  
Shuichi Torii
Keyword(s):  
Experimental Study ◽  
Diffusion Flame ◽  
Fuel Injection ◽  
Numerical Study ◽  
Vacuum Pressure ◽  
Jet Flame ◽  
Injection Nozzle ◽  
Circular Nozzle ◽  
Lift Off

Experimental and numerical study is performed on subsonic hydrogen jet diffusion flame formed from the vertical circular nozzle. Emphasis is placed on the effect of the cavity height formed at the fuel injection nozzle tip on suppression of the flame lift-off. It is found that (i) an increase in the cavity height triggers and enhances a vacuum pressure, (ii) the air from the surroundings is transported naturally into the cavity to replenish the air entrained and consumed by the jet flame, and (iii) the vacuum pressure results in the mitigation of flame lift-off propensity.

scholarly journals Reducing drag on a flat plate subjected to incompressible laminar flow

2019 ◽  
Vol 286 ◽  
pp. 07006
Author(s):  
A. Agriss ◽  
M. Agouzoul ◽  
A. Ettaouil
Keyword(s):  
Fluid Dynamics ◽  
Flat Plate ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Ansys Fluent ◽  
Low Reynolds Numbers ◽  
Computational Fluid Dynamics Cfd ◽  
Corrugated Plates ◽  
The Impact ◽  
Reference Plate

The idea behind this work comes from the question: What is the impact of plate corrugations on drag? In this context, a numerical study of laminar incompressible flow over a flat plate and over corrugated plates is carried out. Numerical analysis is performed for low Reynolds numbers (Re= 10, Re = 50, Re = 100, Re = 500, Re =1000) using the computational fluid dynamics (CFD) software ANSYS FLUENT. Simulations results are compared to each others and with those of the reference plate (flat plate (figure 4a)). Comparisons are made via drag coefficient Cd. This work is the beginning of a study that evaluates the impact of corrugations on drag reduction on a flat plate.

A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

2015 ◽  
Author(s):  
Michael Kolb ◽  
Denise Ahrens ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Time Scale ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Staged Combustion ◽  
Flow Temperature ◽  
Jet Flame ◽  
Stage Combustion ◽  
Lift Off

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multi-stage combustion to lower nitric oxide emissions and enhance turndown ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet lift-off depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K) and jet momentum ratio (6–210). The differences to existing lift-off studies are the high cross flow temperature and applying a premixed jet. The lift-off height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the lift-off height for similar staged combustion systems. A main outcome of this work is that the lift-off height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz number. Furthermore, the ignition delay time scale τign also misses part of the lift-off height mechanism. The presented model uses turbulent time scales, the ignition delay and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

Mastering of the Filling Stage in Low Pressure Sand Casting Process

2018 ◽  
Vol 941 ◽  
pp. 2306-2312
Author(s):  
Antonin Sanitas ◽  
Marie Bedel ◽  
Sofiane Khelladi ◽  
Mohamed El Mansori
Keyword(s):  
Numerical Study ◽  
Casting Process ◽  
Low Pressure ◽  
Simulation Software ◽  
Pressure Casting ◽  
Low Velocity ◽  
Ansys Fluent ◽  
Gas Atmosphere ◽  
Protective Gas ◽  
The Impact

In Low Pressure Casting (LPC), the counter gravity filling at low velocity and the protective gas atmosphere above the metal can potentially reduce gas and oxides entrapment in the metal. However, the relationship between the imposed gas pressure evolution and the melt filling dynamics cannot be analytically determined as it is geometry-dependent. This issue is the missing link to master and automate the filling step in LPC process. In this work, the filling dynamics is numerically investigated for different mold geometries and pressure ramps. The simulation, carried out using ANSYS Fluent® simulation software, is combined with an analytical model. As the results are quantitatively predictive of the filling flow, it permits to develop a numerical study, considering different sudden or progressive section changes and pressure ramps. The impact of the different process parameters on the flow dynamics is analyzed, particularly the transition smoothing impact.

Effect of Fin Inclination Angel on Heat Transfer Improvement in an Annular Space of a Rotor Stator

2021 ◽  
Vol 409 ◽  
pp. 110-122
Author(s):  
Youcef Attou ◽  
Farouk Kebir
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Outer Cylinder ◽  
Convection Flow ◽  
Ansys Fluent ◽  
Annular Channels ◽  
Flow And Heat Transfer ◽  
Inclined Angle ◽  
The Impact ◽  
Heat Transfer Improvement

The present work deals with the numerical investigation of forced convection flow and heat transfer in a finned concentric annulus. The outer cylinder is axially finned while the rotating inner cylinder has a smooth surface. Our research focus on the impact of the fin inclination angle on heat transfer enhancement in rotating annular channels. Tests were carried out for different geometrical configurations using fins with inclined angle (α = 30°, 60°, 90° and 120°). Numerical study is based on effective Reynolds number and Taylor number. The results obtained using the code ANSYS-Fluent with SST k-ω turbulence model show a good agreement between the experimental and the numerical results. In the presence of rotational flow (Ta = 1.14 × 106), the results indicate that α =120° is the optimal case which improves significantly the heat and mass transfer inside the finned channel.

A Model for Predicting the Lift-Off Height of Premixed Jets in Vitiated Cross Flow

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Michael Kolb ◽  
Denise Ahrens ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Time Scale ◽  
Ignition Delay ◽  
Gas Turbines ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Dimensionless Number ◽  
Staged Combustion ◽  
Flow Temperature ◽  
Jet Flame ◽  
Lift Off

Lean premixed single-stage combustion is state of the art for low pollution combustion in heavy-duty gas turbines with gaseous fuels. The application of premixed jets in multistage combustion to lower nitric oxide emissions and enhance turn-down ratio is a novel promising approach. At the Lehrstuhl für Thermodynamik, Technische Universität München, a large-scale atmospheric combustion test rig has been set up for studying staged combustion. The understanding of lift-off (LO) behavior is crucial for determining the amount of mixing before ignition and for avoiding flames anchoring at the combustor walls. This experiment studies jet LO depending on jet equivalence ratio (0.58–0.82), jet preheat temperature (288–673 K), cross flow temperature (1634–1821 K), and jet momentum ratio (6–210). The differences to existing LO studies are the high cross flow temperature and applying a premixed jet. The LO height of the jet flame is determined by OH* chemiluminescence images, and subsequently, the data is used to analyze the influence of each parameter and to develop a model that predicts the LO height for similar staged combustion systems. A main outcome of this work is that the LO height in a high temperature cross flow cannot be described by one dimensionless number like Damköhler- or Karlovitz-number. Furthermore, the ignition delay time scale τign also misses part of the LO height mechanism. The presented model uses turbulent time scales, the ignition delay, and a chemical time scale based on the laminar flame speed. An analysis of the model reveals flame stabilization mechanisms and explains the importance of different time scale.

Study of the Vortex Breakdown in a Conical Swirler Using LDV, LES and POD

2007 ◽  
Author(s):  
Christophe Duwig ◽  
Laszlo Fuchs ◽  
Arnaud Lacarelle ◽  
Matthias Beutke ◽  
Christian Oliver Paschereit
Keyword(s):  
Flow Pattern ◽  
Coherent Structures ◽  
Large Scale ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Flame Stabilization ◽  
Turbulent Fluctuation ◽  
Characteristic Frequencies ◽  
The Impact ◽  
Good Agreement

Modeling and understanding the vortex breakdown is a key issue of modern Lean Premixed Combustors. The main difficulty of the problem is the unsteady behavior of this type of flow: Large structures resulting from vortex breakdown and the swirling shear-layers, affect directly the flame stabilization leading to heat-release fluctuations and combustion instabilities. Consequently, one needs to capture and understand turbulent coherent structures dynamics for designing efficient burners. This task is particularly challenging since it deals with capturing coherent motions within a chaotic system and should be done using state-of-the art numerical and experimental techniques. The present work focuses on the experimental and numerical study of iso-thermal vortex breakdown in a conical swirler. Experimental investigations were performed with 2D Laser Doppler Velocimetry (LDV) and Hotwire Anemometry at the outlet of the combustor model. Averaged velocity fields and RMS values are showing a strong central recirculation zone. In addition, characteristic frequencies of the flow have been exhibited showing the strong influence of large scale turbulent fluctuation on the flow pattern. These measurements showed also the impact of different outlet geometries on the strength and position of the coherent structures of the flow. Further, Large Eddy Simulation (LES) has been used to obtain a 4D description of the flow. Comparison with LDV profiles showed a good agreement, indicating that the LES tool captures accurately the flow. The LES results were then processed for capturing and identifying the coherent structures. Firstly, characteristic frequencies were analyzed. Here also a good agreement with the experimental data was achieved. Secondly the cores of the vortices were visualized providing a good insight into the unsteady flow pattern. Finally, Proper Orthogonal Decomposition (POD) was applied to the 4D field in order to identify the contribution of different large scale fluctuation modes. The presence of the Precessing Vortex Core (PVC) corresponding to a pair of helical structures was captured.

Parametric Study of the Effect of Hinged Connectors on the Behavior of Origami-Inspired Structures Comprised of Sandwich Panels

2015 ◽  
Author(s):  
Zach C. Ballard ◽  
Ashley P. Thrall ◽  
Brian J. Smith
Keyword(s):  
Parametric Study ◽  
Numerical Study ◽  
Sandwich Panels ◽  
Rigid Wall ◽  
Fiber Reinforced Polymer ◽  
Structural Performance ◽  
Uniform Load ◽  
Reinforced Polymer ◽  
Relative Placement ◽  
The Impact

Origami can be a source of inspiration for rapidly deployable, rigid wall shelters. Folding panels comprised of sandwich panels will result in a lightweight, transportable design. The design of connections between panels is critical to the overall structural performance, but can pose a major design challenge. This paper investigates the implementation of hinges for connections between panels. A single panel, comprised of fiber-reinforced polymer faces and a foam core, is restrained by aluminum hinged connectors and subjected to a uniform load. An exhaustive parametric study is performed using a numerical model previously validated by experimental data. The numerical study will facilitate better understanding of the impact of the 1) number, 2) size, and 3) relative placement of connectors on panel behavior, with data comparisons focusing on the longitudinal surface strains and displacements of the panel. This investigation culminates in a set of guidelines for hinged connectors in origami-inspired structures.

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