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 H16: Reacting Flows V: Kinetics |
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Chair: Venkat Raman, University of Texas at Austin Room: 304 |
Monday, November 25, 2013 10:30AM - 10:43AM |
H16.00001: An Assessment of the RCCE for Computationally Efficient Combustion Simulations with Detailed Kinetics Fatemeh Hadi, Mohammad Janbozorgi, Reza H. Sheikhi, Hameed Metghalchi The Rate-Controlled Constrained-Equilibrium (RCCE) method is assessed for detailed kinetics simulations in combustion. The method describes the reacting system dynamics by a relatively small number of rate-controlling reactions and slowly-varying constraints. The unconstrained chemical species are assumed to be in a temporary constrained-equilibrium state and their compositions are determined by maximizing the entropy. The RCCE is applied to predict methane combustion in a constant pressure Partially-Stirred Reactor (PaSR) using 12 constraints and 133 reaction steps. Simulations are carried out over a wide range of initial temperatures and equivalence ratios. The RCCE predictions are compared with those obtained from direct integration of detailed kinetics. It is demonstrated that the set of constraints chosen, accurately represents the methane oxidation kinetics. The effect of mixing on reaction is studied for different residence and mixing time scales. Results show that the RCCE provides accurate prediction of reaction dynamics with various levels of mixing. The RCCE is also shown to significantly reduce the stiffness and the overall computational cost associated with detailed kinetics. [Preview Abstract] |
Monday, November 25, 2013 10:43AM - 10:56AM |
H16.00002: An adjoint approach for determining sensitivity of laminar flames Kalen Braman, Todd Oliver, Venkat Raman Combustion simulations involve a large number of parameters including chemical rate coefficients and species diffusivities. When comparing such simulations to experimental data, it becomes essential to know the relative impact of each of these parameters on the target quantity. For problems that involve a small number of simulation targets and a large number of parameters, adjoint-based sensitivity analysis is highly efficient. In this work, we develop the continuous adjoint equations for a laminar flame configuration, and provide a numerical algorithm for the solution of the dual problem. Simulations of a hydrogen flame are used to test this new approach. Key results pertaining to model validation are discussed. [Preview Abstract] |
Monday, November 25, 2013 10:56AM - 11:09AM |
H16.00003: The Quantum-Kinetic Chemical Reaction Model for Navier-Stokes Codes Michael A. Gallis, Ross M. Wagnild, John R. Torczynski The Quantum-Kinetic chemical reaction model of Bird is formulated as a non-equilibrium chemical reaction model for Navier-Stokes codes. The model is based solely on thermophysical, molecular-level information and is capable of reproducing measured equilibrium reaction rates without using any experimentally measured reaction-rate information. The model recognizes the principal role of vibrational energy in overcoming the reaction energy threshold. The effect of rotational non-equilibrium is introduced as a perturbation to the effect of vibrational non-equilibrium. Since the model uses only molecular-level properties, it is inherently able to predict reaction rates for arbitrary non-equilibrium conditions. This ability is demonstrated in the context of both Navier-Stokes and DSMC codes. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
Monday, November 25, 2013 11:09AM - 11:22AM |
H16.00004: On the potential failure of reduced reaction kinetics Joseph Powers, Samuel Paolucci Severe stiffness of equations modeling advection, reaction, and diffusion in combustion systems has motivated many efforts to filter the primary mechanism inducing the stiffness: the simultaneous presence of fast and slow reaction dynamics. Here, it is demonstrated that a common filtering technique for construction of low dimensional reaction manifolds, connection of equilibria by heteroclinic orbits, can fail. While the method is guaranteed to generate an invariant manifold, the local dynamics far from equilibrium may be such that nearby trajectories are in fact carried away from the identified invariant manifold, thus rendering it to be of limited utility in capturing slow dynamics far from equilibrium. An eigenvalue-based method is described to characterize the local behavior of such invariant manifolds. The method provides a diagnostic tool for evaluating whether a candidate manifold has the desirable properties of being both slow and attractive. A simple model system and a realistic hydrogen-air system are examined; method success and failure are demonstrated. [Preview Abstract] |
Monday, November 25, 2013 11:22AM - 11:35AM |
H16.00005: Investigations of spontaneous ignition of high-pressure hydrogen release based on detailed chemical kinetics Hiroshi Terashima, Mitsuo Koshi, Toshio Mogi, Ritsu Dobashi A numerical simulation of spontaneous ignition of high-pressure release in a length of duct is performed to explore ignition mechanisms. The present study adopts a rectangular duct and focuses on effects of initial diaphragm shape on spontaneous ignitions. The Navier-Stokes equations with a detailed chemical kinetics mechanism are solved in a manner of direct numerical simulation. A conventional numerical approach is used for solving the Navier-Stokes equations, while the chemical source term is integrated by a dynamic multi-timescale method for alleviating the stiffness. Detailed mechanisms of spontaneous ignitions are discussed for various initial diaphragm shapes. For a straight diaphragm shape, the ignition occurs only near the wall region due to the adiabatic wall condition, while, for a largely deformed diaphragm shape, the three ignition events: ignition due to leading shock wave reflection at the wall, hydrogen penetration into shock-heated air near the wall, and deep penetration of hydrogen into shock-heated air behind the leading shock wave, are identified. [Preview Abstract] |
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