NUMERICAL SIMULATION OF THE EFFECT OF INITIAL NONUNIFORMITY AND FLUCTUATIONS OF FUEL CONCENTRATION ON COMBUSTION STABILITY AND NOX AND CO EMISSION IN A LEAN PREMIXED METHANE/AIR COMBUSTOR

2020 ◽  
Author(s):  
K. Ya. Yakubovskiy ◽  
◽  
A. B. Lebedev ◽  
P. D. Toktaliev ◽  
◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Turbulent Flows ◽  
Three Dimensional ◽  
Combustion Stability ◽  
Fuel Concentration ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Low Emission ◽  
Large Eddy ◽  
Co Emission

The effect of initial nonuniformity and fluctuations of fuel concentration on the combustion stability and NOx and CO emission in the model combustion chamber was analyzed with the use of previously developed simple and computationally inexpensive Large Eddy Simulation (LES) methodology for simulation of three-dimensional unsteady turbulent flows with premixed combustion of methane-air mixture in low-emission combustion chamber which geometry is represented by channel with the backward facing step. Typical sizes of the combustion chamber, flow parameters, turbulence level, and method of flame front stabilization are close to those of full-sized industrial combustors.

Three-dimensional study of separated flow over a square cylinder by large eddy simulation

2005 ◽  
Vol 219 (3) ◽  
pp. 225-234 ◽  
Author(s):  
M Farhadi ◽  
M Rahnama
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Separated Flow ◽  
Reynolds Numbers ◽  
Square Cylinder ◽  
Mean Flow ◽  
Central Difference ◽  
Eddy Simulation ◽  
Flow Parameters ◽  
Large Eddy

Large eddy simulation of flow over a square cylinder in a channel is performed at Reynolds numbers of 22 000 and 21 400. The selective structure function (SSF) modelling of the subgrid-scale stress terms is used and the convective terms are discretized using quadratic upstream interpolation for convective kinematics (QUICK) and central difference (CD) schemes. A series of time-averaged velocities, turbulent stresses, and some global flow parameters such as lift and drag coefficients and their fluctuations are computed and compared with experimental data. The suitability of SSF model has been shown by comparing the computed mean flow velocities and turbulent quantities with experiments. Results show negligible variation in the flow parameters for the two Reynolds numbers used in the present computations. It was observed that both QUICK and CD schemes are capable of obtaining results close to those of the experiments with some minor differences.

scholarly journals Large-eddy simulation of contrail evolution in the vortex phase and its interaction with atmospheric turbulence

2015 ◽  
Vol 15 (13) ◽  
pp. 7369-7389 ◽  
Author(s):  
J. Picot ◽  
R. Paoli ◽  
O. Thouron ◽  
D. Cariolle
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Atmospheric Turbulence ◽  
Three Dimensional ◽  
Vertical Direction ◽  
Ambient Air ◽  
Wake Flow ◽  
Initial Flow ◽  
Eddy Simulation ◽  
Large Eddy

Abstract. In this work, the evolution of contrails in the vortex and dissipation regimes is studied by means of fully three-dimensional large-eddy simulation (LES) coupled to a Lagrangian particle tracking method to treat the ice phase. In this paper, fine-scale atmospheric turbulence is generated and sustained by means of a stochastic forcing that mimics the properties of stably stratified turbulent flows as those occurring in the upper troposphere and lower stratosphere. The initial flow field is composed of the turbulent background flow and a wake flow obtained from separate LES of the jet regime. Atmospheric turbulence is the main driver of the wake instability and the structure of the resulting wake is sensitive to the intensity of the perturbations, primarily in the vertical direction. A stronger turbulence accelerates the onset of the instability, which results in shorter contrail descent and more effective mixing in the interior of the plume. However, the self-induced turbulence that is produced in the wake after the vortex breakup dominates over background turbulence until the end of the vortex regime and controls the mixing with ambient air. This results in mean microphysical characteristics such as ice mass and optical depth that are slightly affected by the intensity of atmospheric turbulence. However, the background humidity and temperature have a first-order effect on the survival of ice crystals and particle size distribution, which is in line with recent studies.

Stability analysis and large-eddy simulation of rotating turbulence with organized eddies

1994 ◽  
Vol 278 ◽  
pp. 175-200 ◽  
Author(s):  
Claude Cambon ◽  
Jean-Pierre Benoit ◽  
Liang Shao ◽  
Laurent Jacquin
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Pure Shear ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Eddy Simulation ◽  
Rotating Turbulence ◽  
Special Cases ◽  
Large Eddy ◽  
The Stability

Rotation strongly affects the stability of turbulent flows in the presence of large eddies. In this paper, we examine the applicability of the classic Bradshaw-Richardson criterion to flows more general than a simple combination of rotation and pure shear. Two approaches are used. Firstly the linearized theory is applied to a class of rotating two-dimensional flows having arbitrary rates of strain and vorticity and streamfunctions that are quadratic. This class includes simple shear and elliptic flows as special cases. Secondly, we describe a large-eddy simulation of initially quasi-homogeneous three-dimensional turbulence superimposed on a periodic array of two-dimensional Taylor-Green vortices in a rotating frame.The results of both approaches indicate that, for a large structure of vorticity W and subject to rotation Ω, maximum destabilization is obtained for zero tilting vorticity (½W + 2Ω = 0) whereas stability occurs for zero absolute vorticity (2Ω = 0) These results are consistent with the Bradshaw-Richardson criterion; however the numerical results show that in other cases the Bradshaw-Richardson number $B=2\Omega(W+2\Omega)/W^2$ is not always a good indicator of the flow stability.

Simulating flow separation from continuous surfaces: routes to overcoming the Reynolds number barrier

2009 ◽  
Vol 367 (1899) ◽  
pp. 2885-2903 ◽  
Author(s):  
Michael Leschziner ◽  
Ning Li ◽  
Fabrizio Tessicini
Keyword(s):  
Reynolds Number ◽  
Turbulent Flows ◽  
Major Elements ◽  
Wall Layer ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Rans Models ◽  
High Reynolds ◽  
Near Wall

This paper provides a discussion of several aspects of the construction of approaches that combine statistical (Reynolds-averaged Navier–Stokes, RANS) models with large eddy simulation (LES), with the objective of making LES an economically viable method for predicting complex, high Reynolds number turbulent flows. The first part provides a review of alternative approaches, highlighting their rationale and major elements. Next, two particular methods are introduced in greater detail: one based on coupling near-wall RANS models to the outer LES domain on a single contiguous mesh, and the other involving the application of the RANS and LES procedures on separate zones, the former confined to a thin near-wall layer. Examples for their performance are included for channel flow and, in the case of the zonal strategy, for three separated flows. Finally, a discussion of prospects is given, as viewed from the writer's perspective.

Large‐Eddy Simulation of Three‐Dimensional Flow Structures Over Wave‐generated Ripples

2021 ◽  
Author(s):  
Chuang Jin ◽  
Giovanni Coco ◽  
Rafael O. Tinoco ◽  
Pallav Ranjan ◽  
Jorge San Juan ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Three Dimensional ◽  
Flow Structures ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Eddy Simulation ◽  
Large Eddy
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