Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session AQ: Reacting Flows I: Turbulent Flames |
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Chair: Steve Pope, Cornell University Room: 202B |
Sunday, November 23, 2008 8:00AM - 8:13AM |
AQ.00001: Large-Eddy Simulations of Reacting Liquid Spray Thomas Lederlin, Marlene Sanjose, Laurent Gicquel, Benedicte Cuenot, Heinz Pitsch, Thierry Poinsot Numerical simulation, which is commonly used in many stages of aero-engine design, still has to demonstrate its predictive capability for two-phase reacting flows. This study is a collaboration between Stanford University and CERFACS to perform LES of a realistic spray combustor installed at ONERA, Toulouse. The experimental configuration is computed on the same unstructured mesh with two different solvers: Stanford's CDP code and CERFACS's AVBP code. CDP uses a low-Mach, variable-density solver with implicit time advancement. Droplets are tracked in a Lagrangian point-particle framework. The combustion model uses a flamelet approach, based on two transported scalars, mixture fraction and reaction progress variable. AVBP is a fully compressible solver with explicit time advancement. The liquid phase is described with an Eulerian method. The flame-turbulence interaction is modeled using a dynamically-thickened flame. Results are compared with experimental data for three regimes: purely gaseous non-reacting flow, non-reacting flow with evaporating droplets, reacting flow with droplets. Both simulations show a good agreement with experimental data and also stress the difference and relative advantages of the numerical methods. [Preview Abstract] |
Sunday, November 23, 2008 8:13AM - 8:26AM |
AQ.00002: Numerical Simulation of Highly Turbulent Hydrogen Combustion Andrew Aspden, John Bell, Marc Day The behaviour of hydrogen combustion under highly turbulent conditions is investigated. Simulations are performed using a parallel low Mach number adpative mesh computational method. The study was designed such that the chemical kinetics are well-resolved while relying on an implicit LES approach to capture the turbulence. We present numerical results to validate the approach and discuss the implications for hydrogen combustion in this regime. [Preview Abstract] |
Sunday, November 23, 2008 8:26AM - 8:39AM |
AQ.00003: Simultaneous 3D Volumetric PIV and 2D OH PLIF in the Far-Field of a Nonpremixed Turbulent Jet Flame Mirko Gamba, Noel T. Clemens, Ofodike A. Ezekoye Cinematographic stereoscopic PIV, combined with Taylor's hypothesis, is used to generate quasi-instantaneous volumes of the 3D velocity field in the far field of a turbulent nonpremixed jet flame at a jet exit Reynolds number of 8,000. The 3D data enable computation of the nine components of the velocity gradient tensor and its derived kinematic quantities. The volumetric PIV is combined with simultaneously acquired OH PLIF to mark the instantaneous reaction zone. The combined data sets enable investigation of the relationship between the jet kinematics and the reaction zone. Three-dimensional rendering of regions of intense vorticity and dissipation reveals that sheet-like layers of vorticity and dissipation tend to coincide and are aligned with the OH layers. Due to the stabilizing effect of heat release on this relatively low Reynolds number jet flame, intense dissipation is mostly due to the laminar shear caused by the presence of the flame rather than the strain generated by vortical structures as typically observed in non-reacting jets. It is further observed that both positive and negative dilatation is present and is believed to be mainly due to convection of regions of varying density rather than to instantaneous heat release rate. [Preview Abstract] |
Sunday, November 23, 2008 8:39AM - 8:52AM |
AQ.00004: Statistics and Modeling of the Scalar Dissipation and its Relation to the Filtered Mixture Fraction Robert Knaus, Carlos Pantano, Joseph Oefelein Scalar dissipation is an important quantity for characterizing turbulent mixing and chemical reactions in combustion. It exhibits highly intermittent statistical properties, which have been shown to produce one-point probability density functions that agree well with a log-normal distribution. In large eddy simulation, only the filtered mixture fraction is available to calculate the scalar dissipation. The filtered scalar dissipation, however, is not of primary relevance when modeling phenomena that is sensitive to the smallest scale of the turbulence. Ideally, a statistical approximation of the true scalar dissipation is required. This study examines how filtering mixture fraction affects estimates of the scalar dissipation. Statistics are investigated using DNS databases of turbulent shear layers with different levels of heat release. Using these databases, the effects of filter size to Kolmogorov scale and heat release are determined. A stochastic model of the filtered scalar dissipation that mimics the effects of filtering mixture fraction is then proposed and used as an inverse model to estimate the statistics of the true scalar dissipation. [Preview Abstract] |
Sunday, November 23, 2008 8:52AM - 9:05AM |
AQ.00005: Large Eddy Simulations of Two-phase Turbulent Reactive Flows in IC Engines Araz Banaeizadeh, Harold Schock, Farhad Jaberi The two-phase filtered mass density function (FMDF) subgrid-scale (SGS) model is used for large-eddy simulation (LES) of turbulent spray combustion in internal combustion (IC) engines. The LES/FMDF is implemented via an efficient, hybrid numerical method. In this method, the filtered compressible Navier-Stokes equations in curvilinear coordinate systems are solved with a generalized, high-order, multi-block, compact differencing scheme. The spray and the FMDF are implemented with Lagrangian methods. The reliability and the consistency of the numerical methods are established for different IC engines and the complex interactions among mean and turbulent velocity fields, fuel droplets and combustion are shown to be well captured with the LES/FMDF. In both spark-ignition/direct-injection and diesel engines, the droplet size and velocity distributions are found to be modified by the unsteady, vortical motions generated by the incoming air during the intake stroke. In turn, the droplets are found to change the in-cylinder flow structure. In the spark-ignition engine, flame propagation is similar to the experiment. In the diesel engine, the maximum evaporated fuel concentration is near the cylinder wall where the flame starts, which is again consistent with the experiment. [Preview Abstract] |
Sunday, November 23, 2008 9:05AM - 9:18AM |
AQ.00006: A flamelet-based approach for combustion systems with convective heat-losses Lee Shunn, Parviz Moin A new flamelet method is proposed for modeling turbulence/chemistry interactions in large-eddy simulations (LES) of non-premixed combustion with convective heat-losses. The new method is based on the flamelet/progress-variable approach of Pierce \& Moin (2004) and extends that work to include the effects of thermal-losses on the combustion chemistry. In the new model, chemistry databases are constructed by solving 1D diffusion/reaction equations which have been constrained by scaling the enthalpy of the system between the adiabatic state and a thermally-quenched reference state. The solutions are parameterized and tabulated as a function of the mapping variables: mixture fraction, progress-variable, and normalized enthalpy. The model is implemented in a LES solver which computes the filtered values of the mapping variables, and interpolates other pertinent quantities (such as density and reaction rates) from the chemistry database. The new model is applied to LES of non-premixed methane-air combustion in a coaxial-jet geometry with isothermal wall-conditions to describe heat transfer to the confinement. The resulting velocity, species concentration, and temperature fields are compared to the experiment of Spadaccini, \emph{et al.} (1976) and numerical results from the adiabatic model. [Preview Abstract] |
Sunday, November 23, 2008 9:18AM - 9:31AM |
AQ.00007: Large Eddy Simulation of a Sooting Jet Diffusion Flame Michael Mueller, Guillaume Blanquart, Heinz Pitsch The understanding of soot particle dynamics in combustion systems is a key issue in the development of low emission engines.~ Key mean quantities of the population such as total volume fraction and number density can be predicted without solving for the entire distribution, by just solving for a few moments of the distribution.~ The newly developed Hybrid Method of Moments (HMOM) allows for an efficient and accurate prediction of moments of the soot Number Density Function (NDF).~ This method has been validated for laminar premixed and diffusion flames with detailed chemistry and is now implemented in a semi-implicit low Mach number Navier-Stokes solver.~ A Large Eddy Simulation (LES) of a piloted sooting jet diffusion flame (Delft flame) is performed to study the dynamics of soot particles in a turbulent environment.~ Combustion in the LES is modeled with the Flamelet/Progress Variable Approach (FPVA) to properly account for the effects of temperature on soot formation and growth.~ Profiles of temperature and major species as well as soot volume fraction are compared with experimental measurements.~ In addition, the influence of the turbulent environment on particle shape and size is investigated. [Preview Abstract] |
Sunday, November 23, 2008 9:31AM - 9:44AM |
AQ.00008: Scalar Filtered Density Function for Large Eddy Simulation of a Bunsen Burner S. Levent Yilmaz, Peyman Givi, Peter Strakey The scalar filtered density function (SFDF) methodology is extended for large eddy simulation (LES) of a turbulent, stoichiometric premixed methane/air flame. The SFDF takes account of subgrid scales (SGS) by considering the mass weighted probability density function (PDF) of the SGS scalar quantities. A transport equation is derived for the SFDF in which the effects of chemical reactions appear in closed form. The SGS mixing is modeled via the linear mean square estimation (LMSE) model, and the convective fluxes are modeled via a SGS viscosity. The modeled SFDF transport equation is solved by a hybrid finite-difference/Monte Carlo scheme. A novel irregular domain decomposition procedure is employed for scalable parallelization which facilitates affordable simulations with realistic chemical reactions and flow parameters. Oxidation chemistry is modeled via a 5-step reduced, and a 15-step augmented reduced mechanism. Results are presented of the mean and rms values of the velocity, the temperature, and mass fractions of the major and the minor species. These results are assessed by comparison against laboratory data. [Preview Abstract] |
Sunday, November 23, 2008 9:44AM - 9:57AM |
AQ.00009: Formation and properties of distributed flames Alexei Poludnenko, Vadim Gamezo, Elaine Oran Interaction of flames with turbulence is a ubiquitous process encountered in a wide variety of systems, ranging from terrestrial flames to thermonuclear burning fronts in supernovae. Burning can alter the turbulent field by injecting additional energy on multiple scales thereby modifying its spectral energy distribution. On the other hand, turbulence itself can have pronounced effect on the flame changing its morphology, properties, etc. In this work we present results of detailed numerical and theoretical modeling of the interaction of flames in stoichiometric methane-air and hydrogen-air mixtures with turbulence of varying intensity and spectrum. We demonstrate the transition with increasing turbulent intensity from the laminar flame to the corrugated flamelet and finally to the distributed reaction zone. The latter represents a quasi-steady-state propagating burning front in which thermal conduction and species diffusion are mediated by turbulent transport. We discuss properties of such flames and their potential implications for deflagration-to-detonation transition both in confined and unconfined systems. [Preview Abstract] |
Sunday, November 23, 2008 9:57AM - 10:10AM |
AQ.00010: Measurement of Three-Dimensional Flame Structure by Simultaneous Dual-plane CH PLIF, Single-plane OH PLIF and Stereoscopic PIV Takashi Ueda, Masayasu Shimura, Gyung-Min Choi, Mamoru Tanahashi, Toshio Miyauchi To investigate three-dimensional flame structures of turbulent premixed flame, dual-plane planar laser induced fluorescence (PLIF) of CH radical has been developed. The newly-developed dual-plane CH PLIF is combined with single-plane OH PLIF and stereoscopic particle image velocimetry (SPIV) to clarify the relation between flame geometry and turbulence characteristics. The laser sheets for OH PLIF and SPIV measurement are located at the center of two planes for CH PLIF. The separation between these two CH PLIF planes is selected to $500\mu$m. The measurement was conducted in relatively high Reynolds number methane-air turbulent jet premixed flame. The experimental results show that various three-dimensional flame structures such as the handgrip structure, which has been shown by DNS, are included in high Reynolds number turbulent premixed flame. It was shown that the simultaneous measurement containing newly-developed dual- plane CH PLIF is useful for investigating the three-dimensional flame structure. [Preview Abstract] |
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