Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session E26: Reactive Flows III: Supersonic Combustion and Theory |
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Chair: Heinz Pitsch, Stanford University Room: 31B |
Sunday, November 18, 2012 4:45PM - 4:58PM |
E26.00001: \emph{A priori} and \emph{a posteriori} analyses of the flamelet/progress variable approach for supersonic combustion Amirreza Saghafian, Heinz Pitsch A compressible flamelet/progress variable approach (CFPV) has been devised for high-speed flows. Temperature is computed from the transported total energy and tabulated species mass fractions and the source term of the progress variable is rescaled with pressure and temperature. The combustion is thus modeled by three additional scalar equations and a chemistry table that is computed in a pre-processing step. Three-dimensional direct numerical simulation (DNS) databases of reacting supersonic turbulent mixing layer with detailed chemistry are analyzed to assess the underlying assumptions of CFPV. Large eddy simulations (LES) of the same configuration using the CFPV method have been performed and compared with the DNS results. The LES computations are based on the presumed subgrid PDFs of mixture fraction and progress variable, beta function and delta function respectively, which are assessed using DNS databases. The flamelet equation budget is also computed to verify the validity of CFPV method for high-speed flows. [Preview Abstract] |
Sunday, November 18, 2012 4:58PM - 5:11PM |
E26.00002: The bifurcation of scramjet unstart Ik Jang, Joseph Nichols, Parviz Moin The bifurcation of scramjet unstart is numerically investigated. Near an unstart event, a small change made to the heat released in the combustor causes catastrophic changes in the system. In this talk, this bifurcation structure is studied not only for simple idealized flows but also for a more realistic multi-dimensional model scramjet. In the hysteresis zone of the bifurcation structure, steady but unstable solutions are calculated by means of pseudo-arclength continuation. Pseudo-arclength continuation is performed using Newton-Raphson iteration based on Jacobians computed using an automatic differentiation technique. In addition, eigendecomposition is performed to extract the least stable eigenfunctions describing the system dynamics. Finally, the unstart mechanism and the margins to unstart are evaluated from the bifurcation structure and the linearized system dynamics. [Preview Abstract] |
Sunday, November 18, 2012 5:11PM - 5:24PM |
E26.00003: Quantification of multiple types of uncertainties in the HyShot II scramjet Johan Larsson, Michael Emory, Paul Constantine, Nicolas Kseib, Javier Urzay, Francisco Palacios, Catherine Gorle, Gianluca Iaccarino The talk describes a collaborative effort at quantifying the effects of different types of uncertainties on the pressure rise in the HyShot II scramjet combustor. These uncertainties include the shock-tube conditions (mean and turbulent state, angle-of-attack), the chemical reaction rates in the hydrogen-air chemistry, and errors in the assumed stress-strain relationship in the RANS turbulence model. A physics-based strategy for dimensional reduction is used to make the study computationally feasible. Results include the ranking of different types of uncertainties. [Preview Abstract] |
Sunday, November 18, 2012 5:24PM - 5:37PM |
E26.00004: Flame front as hydrodynamic discontinuity Yasuhide Fukumoto, Snezhana Abarzhi We applied generalized Rankine-Hugoniot conditions to study the dynamics of unsteady and curved fronts as a hydrodynamic discontinuity. It is shown that the front is unstable and Landau-Darrieus instability develops only if three conditions are satisfied (1) large-scale vorticity is generated in the fluid bulk; (2) energy flux across the front is imbalanced; (3) the energy imbalance is large. The structure of the solution is studied in details. Flows with and without gravity and thermal diffusion are analyzed. Stabilization mechanisms are identified. [Preview Abstract] |
Sunday, November 18, 2012 5:37PM - 5:50PM |
E26.00005: The effect of the Darrieus-Landau instability on statistically planar turbulent flames Navin Fogla, Moshe Matalon, Francesco Creta In a recent work, the propagation of premixed flames in weak two dimensional homogeneous turbulent flows was studied by Creta \& Matalon using a hybrid Navier-Stokes/interface capturing technique within the context of a hydrodynamic model, which treats the flame as a surface of density discontinuity. Particular attention was devoted to the Darrieus-Landau (DL) instability, whose effect on turbulent flames has recently been recognized both via experiments and numerical studies. This instability can be triggered in a laboratory setting via changes in pressure and/or fuel type and composition. In the current study, we focus on the effects of the DL instability on turbulent, statistically planar flames. Results are therefore limited to positive Markstein length corresponding to lean hydrocarbon-air or rich hydrogen-air mixtures. We show that conditions under which a laminar flame remains unaffected by the instability, a turbulent flame on the other hand is affected by it. The turbulent flame is observed to exhibit, in addition to the effect of thermal expansion, a nontrivial dependence on the instability, and on the turbulent integral scale both effects modulating, the well established quadratic dependence of turbulent flame speed on turbulence intensity. [Preview Abstract] |
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