Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session J25: Reacting Flows: Extinction, Ignition and Computational Methods |
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Chair: Cheng Huang, University of Kansas Room: 233 |
Sunday, November 20, 2022 4:35PM - 4:48PM |
J25.00001: Implementation and Assessment of Chemical Kinetics Neural ODEs for Combustion Simulations Shubhangi Bansude, Farhad Imani, Reza Sheikhi A data-driven methodology based on neural ordinary differential equations (NODE) is introduced for computationally efficient integration of chemical kinetics stiff ODEs in combustion simulations. The methodology consists of a deep neural network representing the derivatives at the hidden states, integration of which using an ODE solver yields the time evolution of thermochemical variables. A novel approach is established to train the NODE on data generated using a canonical constant pressure homogeneous hydrogen-air reactor. The trained NODE is then evaluated for accuracy and performance on the same reactor. Furthermore, it is applied to a more realistic case of pairwise mixing stirred reactor (PMSR), characterized by complex coupling of chemistry and mixing. The NODE is shown to effectively reduce numerical stiffness, enabling the use of explicit ODE solvers for the integration. It also improves multistep prediction accuracy and robustness, enhancing generalizability to realistic flames. The PMSR results show that, compared to direct integration of detailed kinetics, the NODE can achieve a significant computation time speed up for comparable accuracy. This warrants further extension and application of this approach for large-scale turbulent combustion simulations. |
Sunday, November 20, 2022 4:48PM - 5:01PM |
J25.00002: Analysis of the Radiation Effects from Reacting Metal Particles in Counterflow Diffusion Flame using a Eulerian Lagrangian Numerical Simulation Trushant K Patel, David A Kessler, Brian T Bojko The radiation effects from reacting metal particles plays an important role in amplifying the regression rate of fuels in a solid fuel ramjet. A highly simplified configuration of the diffusion flame structure within a solid fuel ramjet is studied using a counterflow diffusion flame structure. The radiation transport equation is solved numerically using the filtered spherical harmonics method. The rate at which aluminum particles are inputted into the numerical simulation depends on the fuel recession rate and the particle number density in the solid fuel. The location and temperature of the particles are tracked using the Lagrangian equations of motion. A simplified model of combustion of aluminum particles and a two-equation soot model is also implemented to accurately quantify the radiation effects. The radiation effects are coupled with the hydrodynamic solver using a source term in the energy equation. Different 1D and 2D numerical simulations of the counterflow flame structure are performed and validated with existing experimental databases. We quantify the differences in the flame structure in a counterflow diffusion flame with and without radiation. A preliminary 2D numerical analysis of the diffusion flame with a solid fuel combustion chamber is also performed. |
Sunday, November 20, 2022 5:01PM - 5:14PM |
J25.00003: Accelerating Chemical Reactor Design by Leveraging Fuzzy Logic PID Controllers Wayne Strasser, Eric Turman Fuzzy Logic Proportional Integral Derivative (FLPID) controllers was evaluated to determine their ability to reduce convergence times for the computationally expensive globally unsteady model of a low-density polyethylene reactor. The numerical reactor contained millions of computational elements, a rotating stirrer, intricate near-wall geometry, and highly exothermic polymerization kinetics. Catalyst feed rates were instantaneously increased by 50% to evaluate the FLPID’s performance during a hypothetical process excursion. FLPID achieved quasi-steady state (QSS) 54% faster than conventionally tuned PID controllers. Reducing the percent overshoot of the error and rise time of the controller output, the FLPID demonstrated its ability to lower computational cost. FLPID in CFD offers the potential to improve control methods on actual plant scale processes. In particular, the reduction in error overshoot could reduce the likelihood of reactor overheat events, as the temperatures are kept within a tighter operational window. |
Sunday, November 20, 2022 5:14PM - 5:27PM |
J25.00004: Machine learning for combustion system control and simulation Nicholas T Wimer, Marc T Henry de Frahan, Shashank Yellapantula, Ray Grout, Steven Kiyabu Real-world combustion systems are highly complex with scales that span many orders of magnitude making them particularly challenging for numerical simulations. Two large challenges are the numerical simulation and control of these systems in engineering applications under realistic conditions. Machine learning has emerged over the past 5+ years to show immense promise in data science applications and also in many real-world engineering applications. Here, we discuss the recent application of various machine learning techniques to assist in the development of control strategies for compression ignition engines using deep reinforcement learning and also the approximation of chemical kinetics mechanisms using supervised learning for applications in computational fluid dynamics codes. |
Sunday, November 20, 2022 5:27PM - 5:40PM |
J25.00005: Component-based Reduced Order Modeling for Simulations of Large-scale Rocket Engines Cheng Huang Large-scale engineering systems, such as rocket engines, feature complex, multi-scale interactions between multiple physical phenomena, the characterization of which requires detailed computational models. Unfortunately, even with advances in modern computational capabilities, high-fidelity (e.g., large-eddy) simulations of such a system remain out of reach. In this work, a component-based reduced-order modeling framework is established to enable accurate predictions of large-scale rocket engines, which are difficult to simulate at a high-enough level of fidelity but are decomposable into different components. These components can be modeled using a combination of strategies, such as reduced-order models (ROM) or reduced-fidelity full-order models (RF-FOM). Component-based training strategies are developed to construct ROMs for each individual component. These ROMs are then integrated to represent the full system. Notably, this approach only requires high-fidelity simulations of a much smaller computational domain. System-level responses are mimicked via external boundary forcing during training. Model reduction is accomplished using model-form preserving least-squares projections with variable transformation (MP-LSVT) with enhancement through adaptation, which updates the low-dimensional subspaces based on the evaluated dynamics during online calculations to greatly enhance predictive capabilities. The trained ROMs are then coupled and integrated into the framework to model the full large-scale system. The framework is demonstrated on a multi-element rocket combustor configuration and is shown to accurately predict local pressure oscillations, time-averaged, and RMS fields of target state variables, even with geometric changes. |
Sunday, November 20, 2022 5:40PM - 5:53PM |
J25.00006: Non-homogeneous autoignition experimental study for a C3H8/H2 equimolar mixture Hernando A Yepes, Colin Slunecka, Bret Windom, Daniel B Olsen, German J Amador Non-homogeneous autoignition phenomena is a characteristic condition at low temperatures. Flame fronts take place and grow up in the unburned mixture before that volumetric autoignition occurs. An experimental study using a C3H8/H2 equimolar mixture at stoichiometric conditions was carried out to analyze the non-homogeneous ignition in a low-intermediate temperature range (722-865 K) and a fixed pressure (29.3 ± 0.8 bar). The ignition delay time (τ) was measured using the pressure trace in a Rapid Compression Machine. Schlieren images inside the combustion chamber were recorded to perform a qualitative autoignition analysis. Numerical results for τ were obtained using CANTERA. Flame fronts were observed at low temperatures, producing significant disagreement among experimental and numerical results due to high non-homogeneity autoignition. The Sankaran criteria adequately predict the occurrence of non-homogeneous autoignition for the C3H8/H2 mixture. An ignition delay comparison with pure C3H8 suggests that the propane kinetics is still dominant for a 50% H2 fuel addition. |
Sunday, November 20, 2022 5:53PM - 6:06PM |
J25.00007: Spectral element modeling of plasma-assisted ignition using a phenomenological model Islam Kabil, Chao Xu, Tianfeng Lu Non-equilibrium plasma presents a promising tool to reduce ignition delay and extend flame stability limits. To study its influence on turbulent reacting flows, the spectral element code, Nek5000, is extended to include a phenomenological model of energy deposition into gas mixtures. This model assumes ultra-fast gas heating and dissociation via a 2-step mechanism to account for excitation and relaxation of electronically excited N2. Extra source terms are introduced in the governing equations to incorporate this model. Nek5000 is then used to perform 2D simulations of nano-second repetitively pulsed plasma in a premixed CH4/air mixture. First, a comparison of the effect of thermal and non-equilibrium plasma on ignition delay is performed for the same amount of deposited energy. This comparison confirms that the production of active radicals through non-equilibrium plasma greatly enhances ignition compared to thermal pathways. Second, different Reynolds numbers are tested to study the competition between the kinetic effects of plasma and the convection of heat and active radicals. It is found that stronger turbulence tends to reduce the overall reactivity during the transient ignition processes. Last, chemical explosive mode analysis is performed to demarcate ignition zones. |
Sunday, November 20, 2022 6:06PM - 6:19PM |
J25.00008: Laser Induced Spark Ignition Characteristics of a Methane-Oxygen Rocket Combustor Ryan M Strelau, Carson D Slabaugh, Rohan M Gejji The mechanics of laser induced spark ignition of non-premixed gaseous methane and oxygen are investigated. The reactants are injected into an optically accessible combustion chamber from an oxidizer centered shear coaxial injector. High-speed schlieren imaging and deposited laser energy measurements allow for the characterization of ignition behavior at various spark locations throughout the chamber. A two dimensional map of ignition probability is generated from 199 tests completed at 22 different locations. The rate of pressure rise from successful tests reveals two location dependent ignition methods, referred to as "direct" and "indirect". Physical processes occurring over multiple timescales throughout the direct ignition method are first discussed. Ignition outcomes associated with the indirect method are determined by the hydrodynamic ejection protruding from the laser spark, the behavior of which is explored in detail using flow statistics extracted from images taken at a single spark location. The spatial-temporal progression of this jet is found to be dependent on deposited laser energy, leading to a relationship between the amount of energy added to the flow and ignition outcome. General bounds for spark location, deposited laser energy, and ejection behavior are created in order to predict ignition outcomes. Cases that are an exception from these bounds are investigated in detail to understand the cause of unique behavior. These cases lie within regions of the variable space that are susceptible to stochastic elements of the flow. |
Sunday, November 20, 2022 6:19PM - 6:32PM |
J25.00009: Unsteady thermal and chemical response of a porous media burner to fuel supply interruption: application to carbon-free NH3/H2/air flames Guillaume Vignat, Edna R Toro, Thorsten Zirwes, Emeric S Boigne, Matthias Ihme Constructed from open-cell ceramic foams, porous media burners (PMBs) excel at stabilizing flames with poor combustion properties and low pollutant emissions, for applications such as jet engines, process heaters... PMBs rely on heat recirculation through the solid ceramic matrix to enhance thermal diffusion and preheat reactants. Another advantageous feature of PMBs is their ability to store heat in the ceramic matrix: this thermal inertia makes PMBs resilient to disturbances in the fuel supply. We study experimentally relight, the limit case of such disturbances: we interrupt for a few seconds the fuel supply to a PMB. The flame extinguishes, the burner cools down. Upon reintroduction of the fuel, the combustible mixture may reignite if the ceramic foam remains sufficiently hot, and the flame will return to its steady state after a short transient. The fuel of interest is a carbon-free blend of NH3/H2, whose ignition characteristics can be easily varied by adjusting the NH3/H2 ratio. We examine the impact of fuel composition, equivalence ratio and mass flux on the dynamical response of the PMB and propose a simple model to characterize both the thermal transient following extinction, and the subsequent propensity for re-ignition of the burner. |
Sunday, November 20, 2022 6:32PM - 6:45PM |
J25.00010: Investigation of wall effects on combustion noise from a lean-premixed H2/air low-swirl flame using a hybrid LES/APE-RF approach Abhishek L Pillai, Jun Nagao, Takeshi Shoji, Shigeru Tachibana, Takeshi Yokomori, Ryoichi Kurose A hybrid Computational Fluid Dynamics (CFD)/Computational Aero-Acoustics (CAA) approach, in which Large-Eddy Simulation (LES) and the Acoustic Perturbation Equations for Reacting Flows (APE-RF) are employed for the CFD and CAA, respectively, and hence named the hybrid LES/APE-RF approach, is used to analyze the influence of a wall on the combustion noise from a lean-premixed gaseous H2/air low-swirl turbulent jet flame. The wall boundary conditions pertaining to the APE-RF system are formulated to account for acoustic reflections from the wall surface. Results show that the Sound Pressure Level (SPL) spectrum obtained from the hybrid LES/APE-RF simulation is in good agreement with that measured in the experiment. In the LES/APE-RF simulation, the SPL spectrum of combustion noise with a wall plate explicitly changes compared with that without the wall plate. Specifically, the presence of the wall plate tends to ease the peak in the SPL spectrum that existed in the case without the wall plate, and creates a nearly constant SPL within a specific frequency band. Analysis of the heat release rate fluctuations reveals that these phenomena are caused by the absence of a single periodic oscillation of heat release rate. The presence of the wall plate creates an asymmetric flow around the flame and distorts the flame structure, thereby altering the flame fluctuation phenomena. |
Sunday, November 20, 2022 6:45PM - 6:58PM |
J25.00011: Data-Driven Ammonia Combustion Simulation using Neural Ordinary Differential Equations Manabu Saito, Jun Nagao, Jiangkuan Xing, Ryoichi Kurose Detailed combustion mechanisms feature a complex system involving many species and elementary reactions. The complexity of the system usually makes the computational cost very expensive. Recently, Owoyele et al. (Energy and AI, 2022) developed the Neural Ordinary Differential Equations (NODE) for calculations of chemical reactions to accelerate the calculation of hydrogen combustion mechanisms considering 9 species and 21 elementary reactions. However, the application of NODE to chemical reactions was not capable of reproducing the ammonia combustion behavior well, which has much more complex combustion mechanisms involving 59 species and 356 elementary reactions (Okafor et al., Combustion and Flame, 2018). In the present work, the application of NODE is further extended for ammonia combustion mechanisms, and new normalization and training strategies have been proposed. The results show that the optimized model could reproduce the temporal evolution of the 0D ammonia combustion well for wide ranges of equivalence ratios and temperatures and give accurate ignition delay predictions. In addition, the model performance is further explored to investigate the generality to predict untrained data. |
Sunday, November 20, 2022 6:58PM - 7:11PM Author not Attending |
J25.00012: Computational study of the coupling of drift-diffusion, photoionization, and chemistry in a scramjet environment Rajath Shetty, Luca Massa Both experimental and numerical studies have shown that Nanosecond Repetitively Pulsed Discharges (NRPD) can significantly change the combustion field supported by supersonic streams, allowing access to regimes in terms of Mach number and total pressure that would not be possible with regular combustion. Current methods feature simplified plasma-fluid models, which do not consider the effect of flow non-uniformity on the discharge, and one-dimensional radiation models. We present a more complex way to calculate the plasma-induced heat release and radical yield, which incorporates specific kinetic effects of the plasma and radiation. To study this complex non-linear environment, we use three primary tools. First, this model uses Monte Carlo ray tracing (MCRT) to calculate the effects of photoionization of the discharge. Next, multi implicit spectral deferred correction (MISDC) to couple the drift-diffusion equation and reaction to help reduce the splitting errors since this problem incorporates many different time scales for various components. Lastly, in-situ tabulation (ISAT) to solve the Boltzmann equation helps speed up this computational model. Finally, we consider the effect of photoionization and non-equilibrium plasma generated by NRPD on high Mach number flow in a scramjet environment. This model can investigate multidimensional curved electrodes to see how the electrode shape affects the flow in the combustor. |
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