Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session D2: Reacting Flows: General IReacting

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Chair: Shashank Yellapantula, National Renewable Energy Laboratory Room: 402 
Sunday, November 19, 2017 2:15PM  2:28PM 
D2.00001: Influences of the DarrieusLandau instability on premixed turbulent flames Advitya Patyal, Moshe Matalon The propagation of turbulent flames in threedimensional turbulent flows is studied within the context of the hydrodynamic theory. The flame is treated as a surface of density discontinuity with the flow modified by gas expansion resulting from heat released during combustion. The flame is tracked using a levelset method with a propagation speed that depends on the local flame stretch, modulated by a Markstein length. Impact of the DarrieusLandau instability on the topology of the flame surface is studied. It is shown that similar to passive interfaces, flames under the influence of the hydrodynamic instability resort to cylindrical structures with increasing turbulence intensity, even in 3D. The mechanism of modification of vortical structures in the burned gas is identified in terms of the alignments between the vorticity vector, flame surface normal and eigenvectors of the strain rate tensor. The results indicate that the strain rate tensor is intricately coupled with the normal to the flame surface and creates anisotropy in the orientation of vortical structures, which begins to weaken as the turbulent intensity increases. Furthermore, vorticity budgets are used to highlight the relative importance of baroclinic torque due to DarrieusLandau instability. [Preview Abstract] 
Sunday, November 19, 2017 2:28PM  2:41PM 
D2.00002: Onset of DarrieusLandau Instability in Expanding Flames Shikhar Mohan, Moshe Matalon The effect of small amplitude perturbations on the propagation of circular flames in unconfined domains is investigated, computationally and analytically, within the context of the hydrodynamic theory. The flame, treated as a surface of density discontinuity separating fresh combustible mixture from the burnt gas, propagates at a speed dependent upon local curvature and hydrodynamic strain. For mixtures with Lewis numbers above criticality, thermodiffusive effects have stabilizing influences which largely affect the flame at small radii. The amplitude of these disturbances initially decay and only begin to grow once a critical radius is reached. This instability is hydrodynamic in nature and is a consequence of thermal expansion. Through linear stability analysis, predictions of critical flame radius at the onset of instability are obtained as functions of Markstein length and thermal expansion coefficients. The flame evolution is also examined numerically where the motion of the interface is tracked via a levelset method. Consistent with linear stability results, simulations show the flame initially remaining stable and the existence of a particular mode that will be first to grow and later determine the cellular structure observed experimentally at the onset of instability. [Preview Abstract] 
Sunday, November 19, 2017 2:41PM  2:54PM 
D2.00003: Prediction of Combustion Instabilities using a WKBType Solution for the Wave Equation in Inhomogeneous Media Vijaya Krishna Rani, Sarma Rani Linear modal analysis is a widely used reducedorder method to predict combustion instabilities. However, this method is only applicable under the assumption that a combustion system is comprised of chambers with homogeneous meanflow properties. A wellknown analytical solution approach to the onedimensional (1D) wave equation in inhomogeneous media is the WentzelKramersBrillouin (WKB) method, which is based on the assumptions of high frequency and slowly varying flow properties. In this study, a novel WKBtype methodology is developed by relaxing the latter assumption. Solutions are derived for the quasi 1D wave equation in ducts with varying crosssectional area and inhomogeneous meanflow properties. Numerical simulations of the wave equation were also performed. Both the current and classical WKB solutions are compared with the numerical results, as well as known exact solutions. The WKB solution is then applied to predict the longitudinal instabilities in a dump combustor with an area discontinuity. The predicted unstable frequencies are found to be in good agreement with prior experimental and analytical results. [Preview Abstract] 
Sunday, November 19, 2017 2:54PM  3:07PM 
D2.00004: Effects of the fluid flows on enzymatic chemical oscillations Oleg Shklyaev, Victor Yashin, Anna Balazs Chemical oscillations are ubiquitous in nature and have a variety of promising applications. Usually, oscillating chemical systems are analyzed within the context of a reactiondiffusion framework. Here, we examine how fluid flows carrying the reactants can be utilized to modulate the negative feedback loops and time delays that promote chemical oscillations. We consider a model where a chemical reaction network involves two species, X and Y, which undergo transformations catalyzed by respective enzymes immobilized at the bottom wall of a fluidfilled microchamber. The reactions with the enzymes provide a negative feedback in the chemically oscillating system. In particular, the first enzyme, localized on the first patch, promotes production of chemical X, while the second enzyme, immobilized on the second patch, promotes production of chemical Y, which inhibits the production of chemical X. The separation distance between the enzymecoated patches sets the time delay required for the transportation of X and Y. The chemical transport is significantly enhanced if convective fluxes accompany the diffusive ones. Therefore, the parameter region where oscillations are present is modified. The findings provide guidance to designing microscale chemical reactors with improved functionalities. [Preview Abstract] 
Sunday, November 19, 2017 3:07PM  3:20PM 
D2.00005: Investigating the effects of critical phenomena in premixed methaneoxygen flames at cryogenic conditions Abishek Gopal, Shashank Yellapantula, Johan Larsson Methane is increasingly becoming viable as a rocket fuel in the latest generation of launch vehicles. In liquid rocket engines, fuel and oxidizer are injected under cryogenic conditions into the combustion chamber. At high pressures, typical of rocket combustion chambers, the propellants exist in supercritical states where the ideal gas thermodynamics are no longer valid. We investigate the effects of realgas thermodynamics on transcritical laminar premixed methaneoxygen flames. The effect of the realgas cubic equations of state and highpressure transport properties on flame dynamics is presented. We also study realgas effects on the extinction limits of the methaneoxygen flame. [Preview Abstract] 
Sunday, November 19, 2017 3:20PM  3:33PM 
D2.00006: The effects of incident electric fields on counterflow diffusion flames. Mario Di Renzo, Pietro De Palma, Marco Donato de Tullio, Giuseppe Pascazio, Javier Urzay The impingement of electric fields on flames is known to have potential for mitigating combustion instabilities, enhancing flame propagation and decreasing pollutant emissions. A computational analysis of counterflow methaneoxygen laminar diffusion flames impinged by electric fields is performed in this work using axisymmetric numerical simulations, complex transport and a detailed chemistry mechanism. The electric field steers the charged intermediate species, which exchange momentum with the rest of the gas, thereby changing the flow around the flame and creating an ionic wind whereby anions and cations flow towards the corresponding electrodes. As a result, the aerothermal field and scalar dissipation rate undergo variations that may be of significance for the subgridscale modeling of turbulent flames subject to electric fields. The results are found to agree well with previous experiments. [Preview Abstract] 
Sunday, November 19, 2017 3:33PM  3:46PM 
D2.00007: Simulation of the effects of subbreakdown electric fields on the chemical kinetics in nonpremixed counterflow methane/air flames Memdouh Belhi, Hong Im The effects of an electric field on the combustion kinetics in nonpremixed counterflow methane/air flames were investigated via onedimensional numerical simulations. A classical fluid model coupling Poisonâ€™s equation with transport equations for combustion species and electric fieldinduced particles was used. A methaneair reaction mechanism accounting for the natural ionization in flames was combined with a set of reactions that describe the formation of active particles induced by the electric field. Kinetic parameters for electronimpact reactions and transport coefficients of electrons were modeled as functions of reduced electric field via solutions to the Boltzmann kinetic equation using the BOLSIG code. Mobility of ions was computed based on the (n,6,4) and coulomb interaction potentials, while the diffusion coefficient was approximated from the mobility using Einstein relation. Contributions of electron dissociation, excitation and ionization processes were characterized quantitatively. An analysis to identify the plasma regime where the electric field can alter the combustion kinetic was proposed. [Preview Abstract] 
Sunday, November 19, 2017 3:46PM  3:59PM 
D2.00008: Generation of skeletal mechanism by means of projected entropy participation indices Samuel Paolucci, Mauro Valorani, Pietro Paolo Ciottoli, Riccardo Malpica Galassi When the dynamics of reactive systems develop veryslow and veryfast time scales separated by a range of active time scales, with gaps in the fast/active and slow/active time scales, then it is possible to achieve multiscale adaptive model reduction alongwith the integration of the ODEs using the GScheme. The scheme assumes that the dynamics is decomposed into active, slow, fast, and invariant subspaces. We derive expressions that establish a direct link between time scales and entropy production by using estimates provided by the GScheme. To calculate the contribution to entropy production, we resort to a standard model of a constant pressure, adiabatic, batch reactor, where the mixture temperature of the reactants is initially set above the autoignition temperature. Numerical experiments show that the contribution to entropy production of the fast subspace is of the same magnitude as the error threshold chosen for the identification of the decomposition of the tangent space, and the contribution of the slow subspace is generally much smaller than that of the active subspace. The information on entropy production associated with reactions within each subspace is used to define an entropy participation index that is subsequently utilized for model reduction. [Preview Abstract] 
Sunday, November 19, 2017 3:59PM  4:12PM 
D2.00009: A coupled CFD and twophase substrate kinetic model for enzymatic hydrolysis of lignocellulose Nicholas Danes, Hariswaran Sitaraman, Jonathan Stickel, Michael Sprague Costeffective production of fuels from lignocellulosic biomass is an important subject of research in order to meet the world's current and future energy demands. Enzymatic hydrolysis is one of the several steps in the biochemical conversion of biomass into fuels. This process involves the interplay of nonNewtonian fluid dynamics that happen over tens of seconds coupled with chemical reactions that happen over several hours. In this work, we present a coupled CFDreaction model for conversion of cellulose to sugars in a benchtop mixer reactor. A subcycling approach is used to circumvent the large time scale disparity between fluid dynamics and reactions. We will present a validation study of our simulations with experiments for wellmixed and stratified reactor scenarios along with predictions for conversion rates and product concentrations at varying impeller speeds and in scaledup reactors. [Preview Abstract] 
Sunday, November 19, 2017 4:12PM  4:25PM 
D2.00010: Inference of missing data and chemical model parameters using experimental statistics. Tiernan Casey, Habib Najm A method for determining the joint parameter density of Arrhenius rate expressions through the inference of missing experimental data is presented. This approach proposes noisy hypothetical data sets from target experiments and accepts those which agree with the reported statistics, in the form of nominal parameter values and their associated uncertainties. The data exploration procedure is formalized using Bayesian inference, employing maximum entropy and approximate Bayesian computation methods to arrive at a joint density on data and parameters. The method is demonstrated in the context of reactions in the H2O2 system for predictive modeling of combustion systems of interest. [Preview Abstract] 
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