Direct Numerical Simulation of Turbulent Spray Combustion

2000 ◽  
Author(s):  
J. Réveillon
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Combustion Model ◽  
Two Phase ◽  
Complex Interactions ◽  
The Rich ◽  
Global And Local

Abstract Turbulent combustion of two-phase flows is studied by 2D direct numerical simulation. A spray of droplets is injected inside a jet with a preheated coflow. Triple flames appear to represent the global structure of the flame around the spray. Attention is focused upon global and local flame structures and droplet histories. A whole range of combustion phenomena are observed and described. The observed prevailing occurrence, for example, of the rich premixed flame compared to the diffusion flame is of great importance for any turbulent combustion model which must accurately estimate the heat release rate. This prevailing structure depends strongly on the droplet size and combustion. A competition between premixed and diffusion regimes may also occur. It has been shown that in some cases, local clusters of droplets are able either to cross the main flame front and burn in pure oxidizer or to break through the diffusion flame. It is observed that very complex interactions can emerge locally between premixed flames, diffusion flames and droplets.

Modeling of Turbulent Combustion Process and Lean Blowout of Diffusion and Premixed Flames Using a Combined Approach

2009 ◽  
Author(s):  
Yu. G. Kutsenko ◽  
A. A. Inozemtsev ◽  
L. Y. Gomzikov
Keyword(s):  
Diffusion Flame ◽  
Turbulent Combustion ◽  
Diffusion Flames ◽  
Premixed Flames ◽  
Combustion Process ◽  
Combustion Model ◽  
Main Zone ◽  
Lean Blowout ◽  
No Formation ◽  
No Emissions

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper, a new turbulent combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. Within the considered approach this equation has two source terms. These terms are responsible for different conditions of combustion process: diffusion flames and premixed flames, and distributed reacting zones. This paper studies the problem, concerning modeling of lean blowout process of diffusion flame front. To test the proposed combustion model we have simulated lean blowout process inside combustion zone of a gas turbine combustor. Good predictions of lean blowout limits were obtained.

scholarly journals Direct Numerical Simulation of Pore-Scale Trapping Events During Capillary-Dominated Two-Phase Flow in Porous Media

2021 ◽  
Author(s):  
Mosayeb Shams ◽  
Kamaljit Singh ◽  
Branko Bijeljic ◽  
Martin J. Blunt
Keyword(s):  
Numerical Simulation ◽  
Porous Media ◽  
Direct Numerical Simulation ◽  
Complex Geometry ◽  
Flow In Porous Media ◽  
Pore Scale ◽  
Contact Lines ◽  
Two Phase ◽  
X Ray ◽  
Aspect Ratios

AbstractThis study focuses on direct numerical simulation of imbibition, displacement of the non-wetting phase by the wetting phase, through water-wet carbonate rocks. We simulate multiphase flow in a limestone and compare our results with high-resolution synchrotron X-ray images of displacement previously published in the literature by Singh et al. (Sci Rep 7:5192, 2017). We use the results to interpret the observed displacement events that cannot be described using conventional metrics such as pore-to-throat aspect ratio. We show that the complex geometry of porous media can dictate a curvature balance that prevents snap-off from happening in spite of favourable large aspect ratios. We also show that pinned fluid-fluid-solid contact lines can lead to snap-off of small ganglia on pore walls; we propose that this pinning is caused by sub-resolution roughness on scales of less than a micron. Our numerical results show that even in water-wet porous media, we need to allow pinned contacts in place to reproduce experimental results.

scholarly journals Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis

2018 ◽  
Vol 857 ◽  
pp. 270-290 ◽  
Author(s):  
Josef Hasslberger ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Small Scale ◽  
Flow Topology ◽  
Two Phase ◽  
Local Flow ◽  
Interface Curvature

This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.

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