Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Fluid Dynamics
Volume 56, Number 18
Sunday–Tuesday, November 20–22, 2011; Baltimore, Maryland
Session M17: Reacting Flows IV: LES of Turbulent Reacting Flows |
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Chair: Dan Haworth, The Pennsylvania State University Room: 320 |
Tuesday, November 22, 2011 8:00AM - 8:13AM |
M17.00001: Turbulence-Radiation Interactions in Large-Eddy Simulations of Nonpremixed Turbulent Jet Flames D.C. Haworth, A. Gupta, M.F. Modest Large-eddy simulation (LES) has been performed for four piloted nonpremixed turbulent jet flames: a nonluminous laboratory-scale flame, a luminous (sooting) laboratory-scale flame, a nonluminous larger-scale flame, and a luminous larger-scale flame. These flames range from optically thin to moderately optically thick. The simulations feature a transported composition filtered density function (FDF) method to account for the influence of subfilter-scale fluctuations in composition and temperature on resolved chemical reaction rates and radiative emission, and a photon Monte Carlo (PMC) method with line-by-line spectral resolution to model radiation heat transfer including re-absorption. New optimized FDF/PMC algorithms and parallelization strategies have been developed, such that fully coupled LES/FDF/PMC is computationally tractable. The model fully captures both emission and absorption turbulence-radiation interactions (TRI), and is exercised to quantify the contributions of subfilter-scale TRI. For mesh resolutions that are representative of those used in typical turbulent combustion LES studies (approximately 85 percent of the turbulence kinetic energy is resolved), subfilter-scale emission TRI are found to be important in all cases and subfilter-scale absorption TRI are negligible. [Preview Abstract] |
Tuesday, November 22, 2011 8:13AM - 8:26AM |
M17.00002: A fractal dynamic SGS combustion model for turbulent premixed flames Itaru Yoshikawa, Youngsam Shim, Mamoru Tanahashi, Toshio Miyauchi A dynamic subgrid scale (SGS) combustion model for large eddy simulation (LES) of turbulent premixed combustion has been developed based on the fractal characteristics of turbulent premixed flames and the scale separation of turbulence. This model locally predicts the fractal dimension of a flame surface and the local flame surface area. To give the lower limit of the flame surface area, the contribution of dilatation across the flame is also considered. The local turbulent flame speed is then determined supposing the flamelet concept. In the model formulation, the Kolmogorov length scale is described with the grid scale (GS) variables to yield the inner-cutoff of the flame surface. It is achieved by assuming that, in high Reynolds number turbulence, most of the turbulence energy is dissipated in the SGS level and the dissipation balances with the energy production that is given by an SGS turbulence model. A series of static tests have been performed to examine the model by filtered data of direct numerical simulation (DNS). Gaussian or tophat filters with different widths within the range of the inner- and outer-cutoffs of the flame surface are applied as the LES and the test- filters. The results show that the predicted flame surface area agrees well with that extracted from the DNS data regardless of the filter type and the widths. [Preview Abstract] |
Tuesday, November 22, 2011 8:26AM - 8:39AM |
M17.00003: Large-eddy simulation of a three-stream MILD combustion system Jian Zhang, Matthias Ihme, Guowei He Large-eddy simulations (LES) of a three-stream burner system are performed. This burner is operated in the so-called moderate and intense low-oxygen dilution (MILD) combustion regime. An extended flamelet/progress variable (FPV) model is utilized, in which an additional scalar is introduced in order to account for the mixing between the three reactant streams. LES-calculations of three different operating conditions are performed, corresponding to increased levels of oxygen-dilution in the vitiated coflow. The extended FPV model accurately predicts effects of the oxygen-dilution on the flame-structure and heat- release, and model-predictions for temperature and major and minor species are in good agreements with the measurements. [Preview Abstract] |
Tuesday, November 22, 2011 8:39AM - 8:52AM |
M17.00004: Large eddy simulation of an experimental partially-premixed flame configuration using a dynamic nonequilibrium model for subfilter scalar dissipation rate Colleen M. Kaul, Venkat Raman Accurate prediction of nonpremixed turbulent combustion using large eddy simulation (LES) requires detailed modeling of the mixing between fuel and oxidizer occurring at scales not resolved by the LES filterwidth. The scalar dissipation rate, a critical quantity for describing the rate of small scale mixing in conserved scalar combustion models, is dominated by its subfilter component. Nonequilibrium models for the subfilter scalar dissipation rate, which do not assume a local balance between production and dissipation of subfilter scalar variance, typically contain a model coefficient whose optimal value is unknown a priori for a given simulation. Furthermore, conventional dynamic procedures are not useful for estimating its value. An alternative dynamic modeling approach for the model coefficient has been developed based on the transport equation for subfilter scalar variance and validated in a priori tests. Here, the new dynamic nonequilibrium subfilter scalar dissipation rate model is used for simulation of an experimental partially-premixed flame configuration. Results obtained with the new model are compared to predictions using an equilibrium modeling approach for dissipation. [Preview Abstract] |
Tuesday, November 22, 2011 8:52AM - 9:05AM |
M17.00005: LES of Swirling Reacting Flows via the Unstructured scalar-FDF Solver Naseem Ansari, Patrick Pisciuneri, Peter Strakey, Peyman Givi Swirling flames pose a significant challenge for computational modeling due to the presence of recirculation regions and vortex shedding. In this work, results are presented of LES of two swirl stabilized non-premixed flames (SM1 and SM2) [1] via the FDF methodology. These flames are part of the database for validation of turbulent-combustion models [1]. The scalar-FDF is simulated on a domain discretized by unstructured meshes, and is coupled with a finite volume flow solver. In the SM1 flame (with a low swirl number) chemistry is described by the flamelet model based on the full GRI 2.11 mechanism. The SM2 flame (with a high swirl number) is simulated via a 46-step 17-species mechanism. The simulated results are assessed via comparison with experimental data. \\[4pt] [1] Sandia National Laboratories, TNF Workshop Website, Bluff-Body Flames, www.ca.sandia.gov/TNF/bluffbod.html, 2011. [Preview Abstract] |
Tuesday, November 22, 2011 9:05AM - 9:18AM |
M17.00006: Data-Based Optimum Strategies for Combustion Large-Eddy Simulation Hessam Mirgolbabaei, Tarek Echekki In turbulent combustion, moment-based methods have enjoyed widespread use for solving turbulent combustion flows. In these methods, the combustion process is predicted using transport equations for moments (e.g. the mixture fraction) with additional closure needed to determine other thermochemical scalars. The choice of moments is driven by both intuition and experience; but, there is a growing need for optimum strategies to determine these moments. In this work, re-parameterization of the thermochemical state space of combustion flows is performed based on one- dimensional turbulence (ODT) simulations. The re-parameterization identifies optimum transported moments and tabulate key terms in their transport equations. The approach is implemented using principal component analysis (PCA) as a first step towards the evaluation of an optimum set of moments (the principal components) that can represent the thermochemical scalars in the data. Parameters from the PCA analysis can be used to evaluate key terms in the transport equation for these moments. These terms are tabulated using artificial neural network (ANN). [Preview Abstract] |
Tuesday, November 22, 2011 9:18AM - 9:31AM |
M17.00007: A wavelet-based scheme for coupling large-eddy simulation with the one-dimensional turbulence model Yuqiang Fu, Tarek Echekki A wavelet-based scheme for coupling large-eddy simulation (LES) with the one-dimensional turbulence (ODT) model is developed. The LES-ODT approach is a multiscale framework for the simulation of turbulent reacting flows. It is based on the implementation of two solutions: 1) LES for continuity and momentum and 2) ODT for momentum and reactive scalars. Capturing large-scale transport for momentum and scalars is an integral component of the LES-ODT framework The objectives of the wavelet-based scheme are 1) to compound the large-scale velocity field from LES and ODT and 2) to dynamically determine a model parameter in ODT, which governs subgrid scale (SGS) stresses and scalar fluxes. The model is based on the compound wavelet matrix (CWM), which substitutes large-scale physics from LES onto the ODT solution, while maintaining the ODT residual SGS contribution intact. The ODT parameter, which is responsible for controlling the rate of SGS momentum and scalar transport in ODT is dynamically evaluated by comparing wavelet spectra from the ODT and LES solution around the filter cut-off scale. Different strategies are investigated to efficiently evaluate this parameter from an initial guess. The wavelet transform has unique features that enable an efficient and robust implementation of both compounding and ODT parameter estimation. [Preview Abstract] |
Tuesday, November 22, 2011 9:31AM - 9:44AM |
M17.00008: Large-eddy simulation/PDF modeling of a non-premixed CO/H$_2$ temporally evolving jet flame Yue Yang, Haifeng Wang, Stephen B. Pope, Jacqueline H. Chen We report a large-eddy simulation (LES)/probability density function (PDF) study of a non-premixed CO/H$_2$ temporally evolving planar jet flame at Re = 9079 and Da = 0.011 with skeletal chemistry. The flame exhibits strong turbulence- chemistry interactions resulting in local extinction followed by re-ignition. In this study, the filtered velocity field in LES is computed using the NGA code (Desjardins et al., 2008) and the PDF transported equations with the modified Curl's mixing model are solved by the new highly-scalable HPDF code (Wang and Pope, 2011) with second order accuracy in space and time. The performance of the hybrid LES/PDF methodology is assessed through detailed a posteriori comparisons with DNS of the same flame (Hawkes et al., 2007). The comparison shows good agreement of the temporal evolution of the temperature and mass fractions of major chemical species, as well as the prediction of local extinction and re-ignition. In addition, the effects of the subgrid scale model, the mixing model, and grid resolution on turbulence-chemistry interactions are investigated to improve the capabilities of LES/PDF. [Preview Abstract] |
Tuesday, November 22, 2011 9:44AM - 9:57AM |
M17.00009: LES/PDF Approach for Modeling Soot Formation in Turbulent Flames Pratik Donde, Venkat Raman, Michael Mueller, Heinz Pitsch In large eddy simulation based modeling of soot evolution in turbulent flames, the correlations between the gas phase scalars and the soot particles need to be modeled. Typically, the soot population is described in terms of a number density function, which is further parameterized using a finite set of moments. Modeling soot-gas phase correlations essentially implies modeling of the one-time one-point probability density function (PDF) of gas phase scalars and the soot moments. Typically, presumed functional forms for this joint-PDF are used. In this work, a transport equation for the PDF is directly evolved using a Monte-Carlo approach. Simulation of experimental flame configurations including a piloted methane flame and a bluff-body stabilized flame are used to compare the full PDF approach with presumed PDF models. [Preview Abstract] |
Tuesday, November 22, 2011 9:57AM - 10:10AM |
M17.00010: Large Eddy Simulation Modeling and Flamelet Analysis of a Jet in Cross Flow Wai Lee Chan, Hemanth Kolla, Matthias Ihme, Jacqueline Chen Jet in cross flow (JICF) configurations are frequently used as fuel injection strategies in combustion systems, such as gas turbines, boilers, and high-speed propulsion systems. Recently, direct numerical simulations (DNS) have been performed to investigate flame-stabilization mechanisms in a reactive JICF. By utilizing this DNS-database, fundamental modeling assumptions of flamelet-based large eddy simulation (LES) combustion models for application to JICF are evaluated. To this end, a priori and a posteriori studies are performed using steady and unsteady flamelet models to isolate and model combustion flow processes that control transient ignition events and flame stabilization. [Preview Abstract] |
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