A Comparative Study of Flamelet and Finite Rate Chemistry LES for a Swirl Stabilized Flame

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
C. Fureby
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Reactor Model ◽  
Finite Rate ◽  
Eddy Simulation ◽  
Transient Nature ◽  
No Formation ◽  
Stirred Reactor ◽  
Large Eddy ◽  
Large Scale Flow

Present-day demands on combustion equipment are increasing the need for improved understanding and prediction of turbulent combustion. Large eddy simulation (LES), in which the large-scale flow is resolved on the grid, leaving only the small-scale flow to be modeled, provides a natural framework for combustion simulations as the transient nature of the flow is resolved. In most situations; however, the flame is thinner than the LES grid, and subgrid modeling is required to handle the turbulence-chemistry interaction. Here we examine the predictive capabilities between LES flamelet models, such as the flamelet progress variable (LES-FPV) model, and LES finite rate chemistry models, such as the thickened flame model (LES-TFM), the eddy dissipation concept (LES-EDC) model, and the partially stirred reactor model (LES-PaSR). The different models are here used to examine a swirl-stabilized premixed flame in a laboratory gas turbine combustor, featuring the triple annular research swirler (TARS), for which high-quality experimental data is available. The comparisons include velocity and temperature profiles as well as combustor dynamics and NO formation.

LES for NO Prediction in a Propane-Air Turbulent Flame

2007 ◽  
Author(s):  
Sreebash C. Paul ◽  
Manosh C. Paul ◽  
William P. Jones
Keyword(s):  
Large Scale ◽  
Turbulent Flame ◽  
Combustion Process ◽  
Thermal Reaction ◽  
Small Scale ◽  
Governing Equations ◽  
Flamelet Model ◽  
Eddy Simulation ◽  
No Formation ◽  
Large Eddy

Formation of nitric oxide (NO) in a model cylindrical combustor is investigated by applying Large Eddy Simulation (LES) technique. Gaseous propane (C3H8) is injected through a circular nozzle attached at the centre of the combustor inlet and preheated air with temperature of 773K is supplied through the annulus surrounding of the nozzle. The non-premixed combustion process is modelled via conserved scalar approach with laminar flamelet model, while in NO formation model, the extended Zeldovich (thermal) reaction mechanism is taken into account through a transport equation for NO mass fraction. In LES the governing equations are filtered using a spatial filtering approach to separate the flow field into large scale eddies and small scale eddies. The large scale eddies are resolved explicitly while the small scale eddies are modelled via Smagorinsky model.

scholarly journals Large Eddy Simulation of Premixed Stratified Swirling Flame Using the Finite Rate Chemistry Approach

2019 ◽  
Vol 2019 ◽  
pp. 1-15 ◽  
Author(s):  
Yinli Xiao ◽  
Zhengxin Lai ◽  
Wenyan Song
Keyword(s):  
Large Eddy Simulation ◽  
Large Scale ◽  
Swirling Flow ◽  
Flame Surface ◽  
Reactor Model ◽  
Finite Rate ◽  
Eddy Simulation ◽  
Major Species ◽  
Large Eddy ◽  
Swirling Flame

Large eddy simulations of a stratified swirling flow of a Cambridge swirl burner for both nonreacting and reacting cases are conducted using a finite rate chemistry approach represented by a partially stirred reactor model. The large eddy simulation predictions are compared with experimental measurements for velocity, temperature, and concentrations of major species. The agreement is found in overall trend of velocity prediction, but temperature and concentration of major species show slight discrepancies in the central region. Two reduced chemical mechanisms are examined in the present paper with the objective of assessing their capabilities in predicting swirling flame characteristics, and the distinct difference using two mechanisms is found in CO distribution profiles, which is considered the consequence of different kinetics of CO-CO2 equilibrium. Flow structures are qualitatively and quantitatively analyzed with numerical results. Large-scale vortex structures and precession motions are observed in both nonreacting and reacting cases. Frequency of vortex shedding is identified from the point data of instantaneous velocity in the discharging stream-induced shear layer. On this basis, the intensity and frequency of precession motion are shown to be enhanced in the presence of combustion. Large-scale wrinkling of the flame surface is resolved and characterized in the flame zone, and the effect of mixture stratification is then further discussed.

Crackle Noise in Heated Supersonic Jets

2013 ◽  
Vol 135 (5) ◽  
Author(s):  
Joseph W. Nichols ◽  
Sanjiva K. Lele ◽  
Frank E. Ham ◽  
Steve Martens ◽  
John T. Spyropoulos
Keyword(s):  
Large Scale ◽  
Supersonic Jet ◽  
Supersonic Jets ◽  
Scale Model ◽  
Positive Pressure ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Total Temperature ◽  
Large Scale Flow ◽  
Large Eddies

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, “The Effect of Chevrons on Crackle—Engine and Scale Model Results,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.

WAVELET MULTI-RESOLUTION ANALYSIS ON LARGE-EDDY SIMULATION OF TURBURLENT FLOW BEHIND A VEHICLE EXERNAL MIRROR

2013 ◽  
Vol 11 (04) ◽  
pp. 1360007 ◽  
Author(s):  
A. RINOSHIKA ◽  
Y. ZHENG ◽  
E. SHISHIDO
Keyword(s):  
Large Eddy Simulation ◽  
Large Scale ◽  
Three Dimensional ◽  
Wake Flow ◽  
Small Scale ◽  
Three Dimensional Flow ◽  
Eddy Simulation ◽  
Multi Resolution Analysis ◽  
Large Eddy ◽  
Resolution Analysis

The three-dimensional orthogonal wavelet multi-resolution technique was applied to analyze flow structures of various scales around an externally mounted vehicle mirror. Firstly, the three-dimensional flow of mirror wake was numerically analyzed at a Reynolds number of 105 by using the large-eddy simulation (LES). Then the instantaneous velocity and vorticity were decomposed into the large-, intermediate- and relatively small-scale components by the wavelet multi-resolution technique. It was found that a three-dimensional large-scale vertical vortex dominates the mirror wake flow and makes a main contribution to vorticity concentration. Some intermediate- and relatively small-scale vortices were extracted from the LES and were clearly identifiable.

scholarly journals Large Eddy simulation of a supersonic lifted hydrogen flame with perfectly stirred reactor model

2021 ◽  
Vol 230 ◽  
pp. 111441
Author(s):  
Majie Zhao ◽  
Zhi X. Chen ◽  
Huangwei Zhang ◽  
Nedunchezhian Swaminathan
Keyword(s):  
Large Eddy Simulation ◽  
Reactor Model ◽  
Eddy Simulation ◽  
Stirred Reactor ◽  
Large Eddy ◽  
Hydrogen Flame

scholarly journals Statistical Analysis of Dynamic Subgrid Modeling Approaches in Large Eddy Simulation

2021 ◽  
Author(s):  
Mohammad Khalid Hossen ◽  
Asokan Mulayath Variyath ◽  
Jahrul M Alam
Keyword(s):  
Kinetic Energy ◽  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Physical Space ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy

In large eddy simulation (LES) of turbulent flows, the most critical dynamical processes to be considered by dynamic subgrid models to account for an average cascade of kinetic energy from the largest to the smallest scales of the flow is not fully clear. Furthermore, evidence of vortex stretching being the primary mechanism of the cascade is not out of the question. In this article, we study some essential statistical characteristics of vortex stretching and its role in dynamic approaches of modeling subgrid-scale turbulence. We have compared the interaction of subgrid stresses with the filtered quantities among four models using invariants of the velocity gradient tensor. This technique is a single unified approach to studying a wide range of length scales in the turbulent flow. In addition, it also provides a rational basis for the statistical characteristics a subgrid model must serve in physical space to ensure an appropriate cascade of kinetic energy. Results indicate that the stretching mechanism extracts energy from the large-scale straining motion and passes it onto small-scale stretched vortices.

scholarly journals Large-eddy simulation of large-scale structures in long channel flow

2010 ◽  
Vol 661 ◽  
pp. 341-364 ◽  
Author(s):  
D. CHUNG ◽  
B. J. McKEON
Keyword(s):  
Large Scale ◽  
Small Scale ◽  
Mean Velocity ◽  
Large Scale Structures ◽  
Eddy Simulation ◽  
Filter Width ◽  
Half Height ◽  
Large Eddy ◽  
The Mean ◽  
Scale Structures

We investigate statistics of large-scale structures from large-eddy simulation (LES) of turbulent channel flow at friction Reynolds numbers Reτ = 2K and 200K (where K denotes 1000). In order to capture the behaviour of large-scale structures properly, the channel length is chosen to be 96 times the channel half-height. In agreement with experiments, these large-scale structures are found to give rise to an apparent amplitude modulation of the underlying small-scale fluctuations. This effect is explained in terms of the phase relationship between the large- and small-scale activity. The shape of the dominant large-scale structure is investigated by conditional averages based on the large-scale velocity, determined using a filter width equal to the channel half-height. The conditioned field demonstrates coherence on a scale of several times the filter width, and the small-scale–large-scale relative phase difference increases away from the wall, passing through π/2 in the overlap region of the mean velocity before approaching π further from the wall. We also found that, near the wall, the convection velocity of the large scales departs slightly, but unequivocally, from the mean velocity.

Turbulence: the filtering approach

1992 ◽  
Vol 238 ◽  
pp. 325-336 ◽  
Author(s):  
M. Germano
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Stokes Equations ◽  
Small Scale ◽  
Mean Values ◽  
Eddy Simulation ◽  
Turbulent Field ◽  
Large Eddy ◽  
Different Levels

Explicit or implicit filtered representations of chaotic fields like spectral cut-offs or numerical discretizations are commonly used in the study of turbulence and particularly in the so-called large-eddy simulations. Peculiar to these representations is that they are produced by different filtering operators at different levels of resolution, and they can be hierarchically organized in terms of a characteristic parameter like a grid length or a spectral truncation mode. Unfortunately, in the case of a general implicit or explicit filtering operator the Reynolds rules of the mean are no longer valid, and the classical analysis of the turbulence in terms of mean values and fluctuations is not so simple.In this paper a new operatorial approach to the study of turbulence based on the general algebraic properties of the filtered representations of a turbulence field at different levels is presented. The main results of this analysis are the averaging invariance of the filtered Navier—Stokes equations in terms of the generalized central moments, and an algebraic identity that relates the turbulent stresses at different levels. The statistical approach uses the idea of a decomposition in mean values and fluctuations, and the original turbulent field is seen as the sum of different contributions. On the other hand this operatorial approach is based on the comparison of different representations of the turbulent field at different levels, and, in the opinion of the author, it is particularly fitted to study the similarity between the turbulence at different filtering levels. The best field of application of this approach is the numerical large-eddy simulation of turbulent flows where the large scale of the turbulent field is captured and the residual small scale is modelled. It is natural to define and to extract from the resolved field the resolved turbulence and to use the information that it contains to adapt the subgrid model to the real turbulent field. Following these ideas the application of this approach to the large-eddy simulation of the turbulent flow has been produced (Germano et al. 1991). It consists in a dynamic subgrid-scale eddy viscosity model that samples the resolved scale and uses this information to adjust locally the Smagorinsky constant to the local turbulence.

scholarly journals Statistical Analysis of Dynamic Subgrid Modeling Approaches in Large Eddy Simulation

Aerospace ◽  
2021 ◽  
Vol 8 (12) ◽  
pp. 375
Author(s):  
Mohammad Khalid Hossen ◽  
Asokan Mulayath Variyath ◽  
Jahrul M. Alam
Keyword(s):  
Large Eddy Simulation ◽  
Turbulent Flows ◽  
Large Scale ◽  
Joint Probability ◽  
Energy Dissipation Rate ◽  
Statistical Characteristics ◽  
Small Scale ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Individual

In large eddy simulation (LES) of turbulent flows, dynamic subgrid models would account for an average cascade of kinetic energy from the largest to the smallest scales of the flow. Yet, it is unclear which of the most critical dynamical processes can ensure the criterion mentioned above. Furthermore, evidence of vortex stretching being the primary mechanism of the cascade is not out of the question. In this article, we study essential statistical characteristics of vortex stretching. Our numerical results demonstrate that vortex stretching rate provides the energy dissipation rate necessary for modeling subgrid-scale turbulence. We have compared the interaction of subgrid stresses with the filtered quantities among four models using invariants of the velocity gradient tensor. The individual and the joint probability of vortex stretching and strain amplification show that vortex stretching rate is highly correlated with the energy cascade rate. Sheet-like flow structures are correlated with viscous dissipation, and vortex tubes are more stretched than compressed. The overall results indicate that the stretching mechanism extracts energy from the large-scale straining motion and passes it onto small-scale stretched vortices.

scholarly journals Cavitation of Multiscale Vortices in Circular Cylinder Wake at Re = 9500

2021 ◽  
Vol 9 (12) ◽  
pp. 1366
Author(s):  
Fadong Gu ◽  
Yadong Huang ◽  
Desheng Zhang
Keyword(s):  
Circular Cylinder ◽  
Large Scale ◽  
Volume Fraction ◽  
Small Scale ◽  
Cylinder Wake ◽  
Two Phase ◽  
Phase Volume Fraction ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Approximate Frequency

Cavitation characteristics in the wake of a circular cylinder, which contains multiscale vortices, are numerically investigated via Large Eddy Simulation (LES) in this paper. The Reynolds number is 9500 based on the inlet velocity, the cylinder diameter and the kinematic viscosity of the noncavitation liquid. The Schneer–Sauer (SS) model is applied to cavitation simulation because it is more sensitive to vapor–liquid two-phase volume fraction than the Zwart–Gerber–Belamri (ZGB) model, according to theoretical analyses. The wake is quasiperiodic, with an approximate frequency of 0.2. It is found that the cavitation of vortices could inhibit the vortex shedding. Besides, the mutual aggregation of small-scale vortices in the vortex system or the continuous stripping of small-scale vortices at the edge of large-scale vortices could induce the merging or splitting of cavities in the wake.

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