Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session G26: Reacting Flows IV: PDF/FDF |
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Chair: Reza H. Sheikhi, Northeastern University Room: 321 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G26.00001: PDF modeling of chemically reacting flows in a compression-ignition engine Vivek Raja Raj Mohan, Daniel Haworth, Jian Li A transported probability density function (PDF) model is used to simulate the in-cylinder combustion processes in a compression-ignition heavy-duty engine. The flow inside the cylinder in a compression-ignition engine is chemically reacting and highly turbulent. Therefore, the turbulent fluctuations in composition and temperature will influence the mean reaction rates. These turbulence-chemistry interactions (TCI) play an important role in predicting the combustion processes accurately. Recent results from in-cylinder combustion simulations for a compression-ignition engine are compared with measured data for several operating conditions. The PDF model, which takes into account for TCI, predicts the combustion processes more accurately compared to a model which neglects TCI. Marked differences are observed in predicting the flame structure and the pressure and heat-release traces as well as in predicting the emission characteristics. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G26.00002: A Partially-Stirred Batch Reactor Model for Under-Ventilated Fire Dynamics Randall McDermott, Craig Weinschenk A simple discrete quadrature method is developed for closure of the mean chemical source term in large-eddy simulations (LES) and implemented in the publicly available fire model, Fire Dynamics Simulator (FDS). The method is cast as a partially-stirred batch reactor model for each computational cell. The model has three distinct components: (1) a subgrid mixing environment, (2) a mixing model, and (3) a set of chemical rate laws. The subgrid probability density function (PDF) is described by a linear combination of Dirac delta functions with quadrature weights set to satisfy simple integral constraints for the computational cell. It is shown that under certain limiting assumptions, the present method reduces to the eddy dissipation concept (EDC). The model is used to predict carbon monoxide concentrations in direct numerical simulation (DNS) of a methane slot burner and in LES of an under-ventilated compartment fire. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G26.00003: Subfilter Modeling in Spray Combustion Using the Probability Density Function Approach Colin Heye, Venkat Raman A probability density function (PDF) based approach for modeling spray combustion in the large eddy simulation (LES) context is used to study a series of experimental spray flames. Complex coupling of droplet dispersion, evaporation and scalar mixing in turbulent spray-laden flows results in a range of combustion regimes. Prior work has shown that variations in fuel inflow conditions can change the flame structure, however significant simplifications were made in these simulations with the use of steady laminar flamelet based models. In the joint-scalar PDF transport equation, the chemical source term appears closed, and in this work, in situ adaptive tabulation is effectively utilized to calculate component source terms allowing for the impact of finite rate kinetics to be analyzed. Further, the correlation between the evaporation source term and the subfilter scalar PDF is analyzed. Results from a priori direct numerical simulation (DNS) studies and LES calculations will be presented. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G26.00004: Numerical simulations of turbulent jet ignition and combustion AbdoulAhad Validi, Abolfazl Irannejad, Farhad Jaberi The ignition and combustion of a homogeneous lean hydrogen-air mixture by a turbulent jet flow of hot combustion products injected into a colder gas mixture are studied by a high fidelity numerical model. Turbulent jet ignition can be considered as an efficient method for starting and controlling the reaction in homogeneously charged combustion systems used in advanced internal combustion and gas turbine engines. In this work, we study in details the physics of turbulent jet ignition in a fundamental flow configuration. The flow and combustion are modeled with the hybrid large eddy simulation/filtered mass density function (LES/FMDF) approach, in which the filtered form the compressible Navier-Stokes equations are solved with a high-order finite difference scheme for the turbulent velocity and the FMDF transport equations are solved with a Lagrangian stochastic method to obtain the scalar (temperature and species mass fractions) field. The hydrogen oxidation is described by a detailed reaction mechanism with 37 elementary reactions and 9 species. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G26.00005: LES-Based Analysis of Entropy Generation in a Turbulent Nonpremixed Flame Mehdi Safari, Reza H. Sheikhi Entropy generation analysis is an effective means of improving the efficiency of turbulent combustion from the second law of thermodynamics standpoint. Large eddy simulation (LES) of turbulent reacting flows is conducted with inclusion of entropy transport. The filtered form of this equation includes irreversible losses by entropy production due to viscous dissipation, heat conduction, mass diffusion and chemical reaction, all of which appear as unclosed terms. The closure is provided by a novel methodology entitled scalar, entropy filtered density function (SEn-FDF). The SEn-FDF describes the transport and generation of entropy, and is governed by an exact transport equation. This equation is modeled by a set of stochastic differential equations, which is solved by a Lagrangian Monte Carlo method. The main advantage of the SEn-FDF is that it provides closure for all individual entropy generation modes. It also includes the effects of chemical reaction in closed forms. The methodology is applied to a turbulent nonpremixed jet flame (Sandia Flame D) and predictions are assessed against experimental data. Entropy generation modes are obtained from the SEn-FDF and analyzed. [Preview Abstract] |
Monday, November 25, 2013 9:05AM - 9:18AM |
G26.00006: FDF Simulation of the PRECCINSTA Burner Naseem Ansari, Graham M. Goldin, Peter A. Strakey, Peyman Givi Since its original development over a decade ago, the filtered density function (FDF) has experienced widespread application for LES of a variety of turbulent reacting flows. The present work demonstrates that the FDF can now be considered for LES of complex flames in complex combustors. This is done by implementation of the scalar FDF on a domain portrayed by an unstructured grid. The modeled transport equation for the FDF is solved by a Lagrangian Monte Carlo method, coupled with the finite-volume solution of the transport flow variables. The resulting hybrid solver is employed for LES of the PRECCINSTA burner from DLR. The predictive capability of the FDF is assessed by comparison of the Reynolds-averaged statistics of the thermo-chemical variables with measured data. In general, the agreements are very good. This warrants future applications of the methodology for LES of practical combustors. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G26.00007: Parametric modeling studies of turbulent non-premixed jet flames with thin reaction zones Haifeng Wang The Sydney piloted jet flame series (Flames L, B, and M) feature thinner reaction zones and hence impose greater challenges to modeling than the Sanida Piloted jet flames (Flames D, E, and F). Recently, the Sydney flames received renewed interest due to these challenges. Several new modeling efforts have emerged. However, no systematic parametric modeling studies have been reported for the Sydney flames. A large set of modeling computations of the Sydney flames is presented here by using the coupled large eddy simulation (LES) /probability density function (PDF) method. Parametric studies are performed to gain insight into the model performance, its sensitivity and the effect of numerics. [Preview Abstract] |
Monday, November 25, 2013 9:31AM - 9:44AM |
G26.00008: Large Eddy Simulation / Filtered Mass Density Function Modeling of High Pressure Turbulent Hydrogen Flames Richard Miller, Zhiyuan Ma The hybrid Large Eddy Simulation / Filtered Mass Density Function (LES/FMDF) approach to turbulent combustion simulations is extended to include high pressure physics. A posteriori simulations of an existing database of Direct Numerical Simulations (DNS) of high pressure turbulent hydrogen-oxygen and hydrogen-air flames are presented. The DNS include a real fluid equation of state, realistic pressure dependent property models, generalized heat and mass diffusion derived from non-equilibrium thermodynamics and fluctuation theory, and a detailed pressure dependent chemical kinetics mechanism. The geometry considered is a temporally developing reacting shear layer flame. The DNS are conducted at initial shear layer Reynolds numbers up to 4,500 and for pressures as large as 125 atm on numerical meshes up to approximately 3/4 billion grid points. Proper implementation of the LES/FDF approach to simulating the DNS flames is discussed and the simulation results are compared to the filtered DNS results. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G26.00009: A New LES/PDF Method for Computational Modeling of Turbulent Reacting Flows Hasret Turkeri, Metin Muradoglu, Stephen B. Pope A new LES/PDF method is developed for computational modeling of turbulent reacting flows. The open source package, OpenFOAM, is adopted as the LES solver and combined with the particle-based Monte Carlo method to solve the LES/PDF model equations. The dynamic Smagorinsky model is employed to account for the subgrid-scale motions. The LES solver is first validated for the Sandia Flame D using a steady flamelet method in which the chemical compositions, density and temperature fields are parameterized by the mean mixture fraction and its variance. In this approach, the modeled transport equations for the mean mixture fraction and the square of the mixture fraction are solved and the variance is then computed from its definition. The results are found to be in a good agreement with the experimental data. Then the LES solver is combined with the particle-based Monte Carlo algorithm to form a complete solver for the LES/PDF model equations. The in situ adaptive tabulation (ISAT) algorithm is incorporated into the LES/PDF method for efficient implementation of detailed chemical kinetics. The LES/PDF method is also applied to the Sandia Flame D using the GRI-Mech 3.0 chemical mechanism and the results are compared with the experimental data and the earlier PDF simulations. [Preview Abstract] |
Monday, November 25, 2013 9:57AM - 10:10AM |
G26.00010: A New Hybrid FV/Particle Algorithm for PDF Simulations of Turbulent Reacting Flows Reza Mokhtarpoor, Mrtin Muradoglu A new consistent hybrid finite-volume (FV)/particle method is developed for solving the joint PDF equations of turbulent reacting flows. The open source FV package, OpenFOAM, is employed to solve the Favre-averaged mean mass and momentum equations while a particle-based Monte Carlo method is used to solve the fluctuating velocity-turbulence frequency-compositions JPDF transport equation. This work is motivated and designed to eliminate the deficiencies of the hybrid algorithm developed by Muradoglu et al. (1999, 2001). In the earlier hybrid method, a density-based FV algorithm was used to solve the mean flow equations, which has been found to be too dissipative for low-Mach number flows mainly due to the stiffness of the compressible flow equations in this limit. For tackling this problem, the density-based FV solver is replaced with a pressure-based PISO algorithm in the OpenFOAM package. The method is then applied to simulate the Sydney non-swirling and swirling bluff-body stabilized flames and the results are found to be in a good agreement with the experimental data and with the earlier PDF simulations of the same flames. [Preview Abstract] |
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