Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session X34: Reacting Flows: Computational Methods and Simulations |
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Chair: Bruce Perry, National Renewable Energy Laboratory (NREL) Room: 255 F |
Tuesday, November 26, 2024 8:00AM - 8:13AM |
X34.00001: A Hybrid Machine Learning approach for Flamelet Modelling of Turbulent Reacting flows Haresh Chandrasekhar, Ope Owoyele Simulation of turbulent reacting flows requires accurate modeling of complex chemical reactions and their interactions with the turbulent flow field. One of the common approaches to reduce the computational cost of reacting flow simulations is the use multidimensional lookup tables. One such approach is the Unsteady Flamelet Progress Variable (UFPV) approach. While these UFPV tables have demonstrated effectiveness in accurately representing turbulent reacting flows under certain regimes, they are computationally expensive due to the necessity of storing large, multidimensional datasets and performing complex interpolation schemes. This leads to significant memory demands and limitations imposed by the curse of dimensionality, impacting their efficiency and scalability. In response to this limitation, we propose a hybrid machine learning (ML) approach to replace the use of multidimensional UFPV tables, thereby reducing memory requirements and eliminating the need for interpolation schemes. The proposed ML model is validated through a Large Eddy Simulation (LES) of turbulent CH4/air reacting flow, confirming the model’s accuracy. By using this hybrid ML approach, we not only reduce the memory footprint associated with large multidimensional tables but also enhance the model’s scalability and flexibility in handling complex chemical kinetics. |
Tuesday, November 26, 2024 8:13AM - 8:26AM |
X34.00002: Complex manifold-based turbulent combustion models using in-situ adaptive neural network coupled binary trees Stephen Trevor Fush, Israel J Bonilla, Michael E Mueller Manifold-based combustion models can decrease the cost of turbulent combustion simulations by projecting the thermochemical state onto a lower-dimensional manifold, allowing the thermochemical state to be computed separately from the flow solver. Solutions for the manifold equations have traditionally been precomputed and pretabulated, resulting in large memory requirements and significant precomputation cost, even for simple problems. In-Situ Adaptive Manifolds (ISAM) enables solutions to the manifold equations to be computed as the simulation progresses and stored using binary trees with In-Situ Adaptive Tabulation (ISAT), allowing for the use of more general models. While ISAT helps reduce the memory requirements compared to pretabulation approaches, as the model complexity grows, the memory requirements of ISAT databases will still eventually become too large. In this work, binary trees within ISAT are pruned and replaced with neural networks to reduce the memory requirements of the ISAT database. Binary tree pruning and neural network training are conducted on-the-fly in LES in the same spirit as the ISAM approach. Memory use, computational timing, and accuracy with the neural network coupled binary trees are compared to the original ISAM implementation using laboratory-scale flames of varying complexity. |
Tuesday, November 26, 2024 8:26AM - 8:39AM |
X34.00003: A GPU-based spectral-element solver for gaseous low-Mach-number combustion Benjamin Keeton, Chao Xu, Muhsin Ameen A GPU-accelerated high-order spectral element code is developed to solve the low-Mach-number chemically reactive Navier-Stokes equations. The formulation, based on the open-source code nekRS, includes detailed chemistry and transport, and a Strang splitting method to decouple the flow and chemistry sub steps, enabling quicker computations while preserving temporal accuracy. A variety of Runge-Kutta explicit integration techniques are employed for the chemistry integration, and computational speedup numbers are presented. The numerical approach is first validated through simulations of canonical 0D and 1D hydrogen-air flames. To assess code performance for more practical problems encountered in gas turbine combustion, unsteady 3D simulations are conducted for non-premixed hydrogen-air swirling jet flames at moderate Reynolds numbers. Strong and weak scaling results are presented, along with an investigation into the effects of the global equivalence ratio on flame stability. |
Tuesday, November 26, 2024 8:39AM - 8:52AM |
X34.00004: Inherently multi-phase manifold-based combustion models of liquid fuel combustion: Redefinition of mixture fraction and interfacial conditions Philip Satterthwaite, Michael E Mueller Manifold-based combustion models greatly improve the computational cost of reacting flow CFD by projecting the thermochemical state onto a lower-dimensional space. For nonpremixed combustion, this lower-dimensional space is the mixture fraction. While well-defined for single-phase combustion, extensions of nonpremixed manifold models to liquid fuel combustion have seen limited success. Existing approaches use a single-phase combustion model with small adjustments; these include modifications to conserve energy due to evaporative cooling and redefinition of the mixture fraction to account for the non-unity fuel mass fraction at the droplet surface. In this work, a new approach is proposed that is inherently multi-phase. The mixture fraction is redefined to be a conserved scalar with a value of unity at the gas-liquid interface (i.e., droplet surface). Boundary conditions for unity mixture fraction are derived from the fundamental governing equations of species and enthalpy at the gas-liquid interface. Numerical experiments are conducted to demonstrate the capability of the model, and pathways to implementation into CFD and extension to multi-component liquid fuels are discussed. |
Tuesday, November 26, 2024 8:52AM - 9:05AM |
X34.00005: Time varying inflow generation using adjoint-based PDE constrained optimization for reactive flow simulations VIJAYAMANIKANDAN VIJAYARANGAN, Hong G Im This study provides a time-varying inflow generation methodology for high-fidelity numerical simulations. The present work utilizes the variational principles and adjoint-based partial differential equation (PDE) constrained optimization techniques. The optimization consists of two steps: forward integration and backward integration. The forward process integrates the given dynamical system, and the backward process integrates the adjoint state of the discrete dynamical system reverse in time. The current model-free approach provides an accurate time-varying inflow boundary condition for high-fidelity numerical simulations based on the experimental statistics. The proposed methodology is demonstrated for the highly three-dimensional swirl-dominated burner's jet and swirl inflow conditions. |
Tuesday, November 26, 2024 9:05AM - 9:18AM |
X34.00006: Abstract Withdrawn
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Tuesday, November 26, 2024 9:18AM - 9:31AM |
X34.00007: Using Frame Transformation to Enhance Analysis of Quasi-Periodic Rotating Detonation Rocket Engine Behavior Bill D. Caraway, Arne J Pearlstein Rotating detonation rocket engines (RDRE) often have quasi-periodic longtime behavior, which is significantly more difficult to analyze than periodic behavior because not all pairs of frequencies present are rationally related. For certain classes of quasi-periodic spatio-temporal waves, we have previously shown (Phys. Rev. E 106, 024607, 2022) that the frequency content is dependent, in predictable ways, on the frame in which the behavior is observed. We show that noisy pressure fields from RDRE simulations exhibit this behavior, and obtain the relationships between the frequency content of the pressure field and the angular velocity of the rotating frame. Using these relationships, we show how rotating frames can be used to better extract the frequencies, by increasing the separation between very close frequency peaks. Increasing this separation reduces spectral leakage, which is particularly desirable when the time series available are not long. We are also able to identify rotating frame velocities in which the pressure field is temporally periodic. This reduced complexity offers several benefits, one of which is that the behavior can now be fully captured in finite time, which is not possible for quasi-periodic behavior. |
Tuesday, November 26, 2024 9:31AM - 9:44AM |
X34.00008: A numerical investigation of nonpremixed laminar, swirling, hydrogen-air jet flames Brandon Li, Benjamin Keeton, Antonio L Sanchez, Forman A Williams To better understand combustion stabilization in hydrogen-fueled gas turbines, numerical simulations using the spectral element-code Nek5000 are performed at moderate Reynolds numbers to characterize nonpremixed diffusion flames in axisymmetric configurations involving a swirling hydrogen jet discharging into a preheated coflow stream of air diluted with nitrogen. The conservation equations are formulated using the low Mach number approximation, with a mixture-averaged model employed to describe molecular transport. Fuel oxidation is described using both detailed chemistry and an explicit one-step reduced mechanism previously derived by assuming all chemical intermediates to maintain steady state, an approximation afforded by the high-pressure conditions existing in gas-turbine combustion chambers. The interplay of vortex breakdown with various flame behaviors, such as liftoff and blowoff, is characterized as a function of the jet-to-coflow velocity ratio, the swirl number and the Damkohler number. The results clearly demonstrate the predictive capability of the one-step chemistry in connection with the numerical computation of hydrogen combustion in high-pressure environments. |
Tuesday, November 26, 2024 9:44AM - 9:57AM |
X34.00009: Two-phase flow modeling of thermal frontal polymerization Maged Ahmed Faragalla, Miltiadis V. Papalexandris Thermal frontal polymerization is a process that converts a monomer solution (liquid) into solid polymer via propagation of a reaction front. Initiated by a brief local energy source, the front is self-sustained by virtue of the heat generated by the polymerization reaction. Allowing for rapid and uniform synthesis, this process has gained interest as a fast and energy-efficient solution for manufacturing of composites. However, the front is subject to thermo-convective and chemical instabilities which can degrade the quality of the end polymer product and even extinguish the entire process. Currently, our understanding of the front dynamics is incomplete. |
Tuesday, November 26, 2024 9:57AM - 10:10AM |
X34.00010: Examining the Impact of Microenvironments on Large-Scale Bioreactor Processes Julia Ream, Nicholas T Wimer, Mohammad J Rahimi, William T Cordell, Hari Sitaraman, Marc Day, Davinia Salvachúa Large-scale bioreactors play a critical role in enhancing the bioeconomy and advancing biotechnology-related industries. In transitioning from the laboratory- to the industrial-scale, the complexity of these fluid systems increases, making microbial performance harder to predict. Computational fluid dynamics is a vital tool in exploring how the change in dynamics during scale-up affects these bioprocesses. We investigate the formation and impact of microenvironments within bioreactors of increasing size and their influence on microbe cell production. The investigation is based on a multiphase solver we developed within OpenFOAM that couples multi-component transport and reaction processes specific to the organism P. putida, incorporating experimental data through metabolic model parameters. Preliminary studies target microenvironment development within a range of bioreactor sizes and configurations. |
Tuesday, November 26, 2024 10:10AM - 10:23AM |
X34.00011: Chemically Reacting Flow Modeling of a Hybrid Rocket Thirumaran Varathalingarajah, Todd Harman, Alex G Novoselov This study investigates simulation strategies for chemically reacting flows in hybrid rocket systems, which leverage the advantages of both gas and solid-fueled propulsion. Gaseous nitrous oxide (N₂O) is utilized as the oxidizer and solid acrylonitrile butadiene styrene (ABS) is utilized as the fuel grain. Simulations are tailored to an experimental setup designed for thrust levels below 100 pounds and accommodating dual gas oxidizer configurations. The Uintah: MPMICE Computational Framework is employed to simulate chemically reacting flow dynamics, multiphase phenomena, and fluid-structure interactions. Fuel regression rates are quantified using an Arrhenius-type equation and a two-phase chemistry model specific to ABS, calibrated with limited experimental data. The study assesses how surface gasification and combustion models influence fuel grain regression rates, emphasizing validation against experimental measurements for accuracy and reliability. |
Tuesday, November 26, 2024 10:23AM - 10:36AM |
X34.00012: Physical Mechanisms in Combustion for Ablating Carbon-fiber Composite Thermal Protection Tulio Rodarte Ricciardi, Kunkun Tang, Jonathan Ben Freund Thermal protection systems based on light-weight carbon-fiber composites are attractive in aerospace propulsion applications, though their use depend on several physical mechanisms, which their extreme conditions make difficult to diagnose. To assess these mechanisms, a model system is considered in which candidate materials are placed above a flat-flame McKenna burner. A corresponding slug calorimeter provides a measure of the heat flux. Point-to-point comparisons between detailed simulations and the experiments highlight important components of the physics coupling. Heat conduction and species diffusion back to the burner are shown to be an unexpectedly relevant factor. The relative importance of additional physics is assessed by studying chemical kinetics mechanisms and transport models, from unitary Lewis number to multicomponent diffusion including Soret effects. Their effect on flow dynamics, flame structure, products temperature and heat flux into the calorimeter is discussed. Physics model integration for ablation of a phenolic permeated carbon fiber material is also presented. |
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