Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G12: Turbulent and Chemically-reacting Flow Modeling II |
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Chair: William Jones, Imperial College London Room: 303 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G12.00001: Honoring Ted O’Brien: High order methods for filtered and probability density function models Gustaaf Jacobs The systems of partial differential equations that govern probability and filtered density function models can be solved directly using numerical methods. Oftentimes, this type of system is also solved using a combination of Monte-Carlo and stochastic differential equations. If the density function model is coupled with another model that has feedback, as can occur in multi-physics or multi-phase environments, then the numerical coupling must be consistent for both approaches to obtain an accurate numerical solution. In this talk, I will discuss recent progress in the development of high order accuracy methods for models governing, chemically reaction and/or particle-laden, high-speed flows with shocks. High order distribution functions and weighted interpolations combined with spectral elements methods are presented and are shown to give accurate results for time-dependent problems that require long time integration. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G12.00002: Combustion LES and the stochastic fields method William Jones Honoring Ted O’Brien. The large eddy pdf equation formulated by Gao and O'Brien is a powerful method for simulating turbulent combustion. No assumptions are required regarding specific modes of burning so the method is applicable to non-premixed and partially and perfectly premixed flames including ignition and extinction. The large eddy pdf equation involves a large number of independent variables so that stochastic methods are required for its solution; in the present work the stochastic fields method is utilised. It has been applied to simulate the evolution of self-excited thermo-acoustic instabilities in a gas turbine model combustor, using a fully compressible formulation. An unstable operating condition in the PRECCINSTA combustor, involving flame oscillation driven by thermo-acoustic instabilities, is the chosen target configuration. The flame's self-excited oscillatory behaviour is successfully captured without any external forcing being involved. Power spectral density analysis of the oscillation reveals a dominant thermo-acoustic mode at a frequency of 300~Hz providing remarkably good agreement with experimental observations. Moreover, the predicted limit-cycle amplitude closely matches the experimental value obtained with rigid metal combustor side walls. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G12.00003: Physics-Based vs. Data-Driven Modeling for Turbulence and Combustion Sharath Girimaji Honoring Ted O'Brien: Ted O'Brien had a long and distinguished career in modeling and computing chemically reacting turbulent flows. He made important contributions toward modeling/computation of auto-ignition in turbulent mixtures, conditional scalar dissipation, PDF (probability density function) methods and mapping closure methods. Currently, drive toward use of data-driven models is pervasive in nearly all fields involving complex phenomena including turbulent combustion. This presentation will discuss some of the benefits and challenges of using data-driven models for prediction of reacting turbulent flows. For a variety of turbulence and combustion features, we will compare the strengths and weaknesses of data-driven modeling against that of physics-based modeling. Specifically we will examine the general capabilities of data-driven approaches for handling (i) distant interactions - specifically non-local effects due to the elliptic nature of pressure and (ii) purely local process of chemical reactions. The talk will conclude with some recommendations on synergistically combining physics-based and data-driven approaches for developing predictive tools for turbulence and combustion. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G12.00004: Differential diffusion modelling in transported PDF simulations of turbulent flames Zhuyin Ren, Hua Zhou, Tianwei Yang Honoring Ted O'Brien. The modelling strategy to incorporate differential diffusion effects in transported density function method (PDF), particularly in the context of large eddy simulation (LES) is proposed. Differential diffusion at the filter scale is resolved by the mean drift term in composition equations, while subgrid differential diffusion is modelled by the augmented mixing models that can account for differential mixing rates for each individual species. Both RANS/PDF and LES/FDF simulations of a jet-in-hot-coflow methane-hydrogen flame have been performed to investigate the effects of differential diffusion on flame characteristics. [Preview Abstract] |
Sunday, November 24, 2019 4:40PM - 4:53PM |
G12.00005: Mathematical Models For Eulerian Conditional Statistics in a Complex Turbulent Flow James Hill, Emmanuel Hitimana, Michael Olsen, Rodney Fox Honoring Ted O'Brien. Conditional moment closure (CMC) methods were developed for predicting turbulent reacting flows. However, conditional averages appear as unclosed terms that need to be modeled. In the present work the linear approximation and PDF gradient models were used to predict the conditional mean velocity and mixture fraction and compare with experimental data obtained for a macroscale multi-inlet vortex chemical reactor (macro-MIVR) using laser diagnostic techniques. The results for velocity conditioned on mixture fraction show that the linear model works well in a low turbulence region away from the reactor center. The PDF model with an isotropic turbulent diffusivity performs poorly for the tangential and axial conditional velocities, but a modified version that considers three components of turbulent diffusivity is better. Furthermore, the mixture fraction conditioned on the velocity vector components has a more linear behavior near the reactor center, where the probability density function (PDF) of the mixture fraction is close to a Gaussian distribution. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G12.00006: On the kinematics of scalar iso-surfaces in a turbulent, temporally developing jet Brandon Blakeley, Weirong Wang, Duane Storti, James Riley The kinematics and dynamics of scalar iso-surfaces in turbulent flows is of fundamental importance for a number of problems, e.g., the stoichiometric flame surface in non-premixed combustion or the turbulent/non-turbulent interface in turbulent shear flows. We investigate the effects of turbulence on iso-surfaces by examining the surface area density, $\Sigma$, and its evolution. Using direct numerical simulation of a temporally developing jet and a novel algorithm for evaluating iso-surface properties, we report on the direct computation of $\Sigma$ and the terms in its transport equation. Iso-surface properties, such as the surface area, are evaluated by converting the surface integrals to volume integrals on a regularly-sampled grid. In particular, we analyze the behavior of two different scalar iso-surfaces: the vorticity magnitude, which represents the T/NT interface in a turbulent free shear flow, and a passive scalar field which represents an inert tracer such as dye concentration or the mixture fraction. Differences between the evolution of the two iso-surfaces will be addressed, such as the production of iso-surface area due to the turbulent strain-rate and the destruction of iso-surface area due to the combined effects of diffusion and surface curvature. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G12.00007: Investigation of Two-Phase Supersonic Combustion in Hypersonic Flight Foluso Ladeinde The author’s initial studies on compressible turbulence and combustion in high-speed flows were done via DNS in collaboration with the Late Professor Edward E. O’Brien in several joint publications on the topic. However, the author’s focus has evolved, and the transport of momentum, energy, and chemical species in supersonic spray combustion for systems that approximate the scramjet engine in hypersonic flight is of current interest. Many advantages can be derived from the use of liquid fuels, such as the higher heat release and ease of storage and handling. The system in question is complicated by the interaction of many effects, including those due to combustion, evaporation, turbulence, shock waves, and their interactions. Consequently, not many studies have addressed the issues. Based on the parameters for the application of interest, the point-particle approach via the Eulerian-Lagrangian formulation is followed in the present endeavor. This approach introduces explicit force and energy sources, some of which involve history integrals. The significance of these sources is investigated in terms of their roles in the rather complex drop breakup mechanism in the presence of shockwaves, and the eventual evaporation and combustion to provide the needed propulsive force. The progress made by the author will be reported. [Preview Abstract] |
Sunday, November 24, 2019 5:19PM - 5:32PM |
G12.00008: Evaluation of Entropy Transport Equation in Turbulent Jet Flames using Filtered Density Function Mehdi Safari, Reza Sheikhi Evaluation of entropy provides a tool to optimize performance of combustion systems through the second law of thermodynamics. In turbulent reacting flows, entropy is generated due to viscous dissipation, heat conduction, mass diffusion and chemical reaction. In large eddy simulation (LES), all of these effects along with subgrid scale (SGS) entropy flux, appear as unclosed terms. The closure is provided by utilizing a special form of filtered density function (FDF) called entropy FDF (En-FDF). The prime advantage of using the En-FDF is that it provides closure for all individual entropy generation effects as well as scalar-entropy statistics. It also includes the effect of chemical reaction in a closed form. The En-FDF transport is modeled by a set of stochastic differential equations. The numerical solution procedure is based on a hybrid form of finite difference and Monte Carlo solvers in which the filtered transport equations are solved by the finite difference solver and the stochastic differential equations are solved by a Lagrangian Monte Carlo procedure. This methodology is applied to a turbulent nonpremixed jet flame and sources of irreversibilities are predicted and analyzed. [Preview Abstract] |
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