A Consistent Hybrid LES-RANS PDF Method for Non-premixed Flames

AbstractThe computational demanding LES methods have widely demonstrated their reliability in the description of large scale unsteady phenomena in turbulent reactive flows. RANS Transported Probability Density Function (TPDF) methods treat the nonlinear chemical reactions in closed form on relatively coarse grids and using a smaller number of stochastic particles. Combining the two approaches, a hybrid LES-RANS PDF method to predict non-premixed turbulent flames is presented. In this method a LES, based on Smagorinsky's model and steady flamelet, is performed; subsequently, the calculated flow-field is used to drive the RANS-TPDF equation, which is closed at the joint scalar level and based on a Lagrangian Monte Carlo scheme. The required velocity and turbulent quantities for RANS simulation are estimated from the resolved LES and an algebraic model based on dimensional analysis and the mixing length hypothesis. The results of the velocity, turbulent kinetic energy and mixture fraction show that the consistency of the method is achieved

Effect of the Hydration Shell on the Carbonyl Vibration in the Ala-Leu-Ala-Leu Peptide

The vibrational spectrum of the Ala-Leu-Ala-Leu peptide in solution, computed from first-principles simulations, shows a prominent band in the amide I region that is assigned to stretching of carbonyl groups. Close inspection reveals combined but slightly different contributions by the three carbonyl groups of the peptide. The shift in their exact vibrational signature is in agreement with the different probabilities of these groups to form hydrogen bonds with the solvent. The central carbonyl group has a hydrogen bond probability intermediate to the other two groups due to interchanges between different hydrogen-bonded states. Analysis of the interaction energies of individual water molecules with that group shows that shifts in its frequency are directly related to the interactions with the water molecules in the first hydration shell. The interaction strength is well correlated with the hydrogen bond distance and hydrogen bond angle, though there is no perfect match, allowing geometrical criteria for hydrogen bonds to be used as long as the sampling is sufficient to consider averages. The hydrogen bond state of a carbonyl group can therefore serve as an indicator of the solvent’s effect on the vibrational frequency

Assessment of flamelet manifolds for turbulent flame-wall interactions in Large-Eddy Simulations

A turbulent side-wall quenching (SWQ) flame in a fully developed channel flow is studied using Large-Eddy Simulation (LES) with a tabulated chemistry approach. Three different flamelet manifolds with increasing levels of complexity are applied: the Flamelet-Generated Manifold (FGM) considering varying enthalpy levels, the Quenching Flamelet-Generated Manifold (QFM), and the recently proposed Quenching Flamelet-Generated Manifold with Exhaust Gas Recirculation (QFM-EGR), with the purpose being to assess their capability to predict turbulent flame-wall interactions (FWIs), which are highly relevant to numerical simulations of real devices such as gas turbines and internal combustion engines. The accuracy of the three manifolds is evaluated and compared a posteriori, using the data from a previously published flame-resolved simulation with detailed chemistry for reference. For LES with the FGM, the main characteristics such as the mean flow field, temperature, and major species can be captured well, while notable deviations from the reference results are observed for the near-wall region, especially for pollutant species such as \ce{CO}. In accordance with the findings from laminar FWI, improvement is also observed in the simulation with QFM under turbulent flow conditions. Although LES with the QFM-EGR shows a similar performance in the prediction of mean quantities as LES with QFM, it presents significantly better agreement with the reference data regarding instantaneous thermo-chemical states near the quenching point. This indicates the necessity to take into account the mixing effects in the flamelet manifold to correctly capture the flame-vortex interaction near the flame tip in turbulent configurations. Based on the findings from this study, suitable flamelet manifolds can be chosen depending on the aspects of interest in practical applications

Targeting phosphoglycerate kinases by tatridin A, a natural sesquiterpenoid endowed with anti-cancer activity, using a proteomic platform

Tatridin A (TatA) is a germacrane sesquiterpenoid containing one E-double bond and one Z-double bond in its 10-membered ring, which is fused to a 3-methylene-dihydrofuran-2-one moiety. Tatridin A bioactivity has been poorly investigated despite its interesting chemical structure. Here, a functional proteomic platform was adapted to disclose its most reliable targets in leukemia monocytic cells, and phosphoglycerate kinases were recognized as the most affine enzymes. Through a combination of limited proteolysis and molecular docking, it has been discovered that tatridin A interacts with the active domains of phosphoglycerate kinase 1, altering its hinge region, and it can be accountable for tatridin A inhibition potency on enzyme activity. A more detailed tatridin A biological profile showed that it is also fully active against gastric cancer cells, downregulating the mRNA levels of chemokine receptor 4 and β-catenin and inhibiting the invasiveness of living KATO III cells as a direct consequence of phosphoglycerate kinase 1 antagonism

Numerical Investigation on the Effect of the Oxymethylene Ether-3 (OME3) Blending Ratio in Premixed Sooting Ethylene Flames

Synthetic fuels, especially oxygenated fuels, which can be used as blending components, make it possible to modify the emission properties of conventional fossil fuels. Among oxygenated fuels, one promising candidate is oxymethylene ether-3 (OME₃). In this work, the sooting propensity of ethylene (C₂H₄) blended with OME₃ is numerically investigated on a series of laminar burner-stabilized premixed flames with increasing amounts of OME₃, from pure ethylene to pure OME₃. The numerical analysis is performed using the Conditional Quadrature Method of Moments combined with a detailed physicochemical soot model. Two different equivalence ratios corresponding to a lightly and a highly sooting flame condition have been investigated. The study examines how different blending ratios of the two fuels affect soot particle formation and a correlation between OME₃ blending ratio and corresponding soot reduction is established. The soot precursor species in the gas-phase are analyzed along with the soot volume fraction of small nanoparticles and large aggregates. Furthermore, the influence of the OME₃ blending on the particle size distribution is studied applying the entropy maximization concept. The effect of increasing amounts of OME₃ is found to be different for soot nanoparticles and larger aggregates. While OME₃ blending significantly reduces the amount of larger aggregates, only large amounts of OME₃, close to pure OME₃, lead to a considerable suppression of nanoparticles formed throughout the flame. A linear correlation is identified between the OME₃ content in the fuel and the reduction in the soot volume fraction of larger aggregates, while smaller blending ratios may lead to an increased number of nanoparticles for some positions in the flame for the richer flame condition

Large eddy simulation of the Delft Adelaide Flame III using a quadrature-based method of moments

In this work, the recently developed split-based Extended Quadrate Method of Moments (S-EQMOM) is combined with a LES/presumed PDF-based flamelet/progress variable approach to achieve the predictions of soot particle size distributions in a turbulent non-premixed jet flame. The advantage of the S-EQMOM is that a continuous soot particle number density function (NDF) is able to be reconstructed by superimposing kernel density functions (KDFs) of presumed shape (gamma or log-normal distribution) that interact through the particle coagulation. Moreover, the S-EQMOM primary nodes are determined individually for each KDF yielding improvement in the numerical robustness compared to classical EQMOM. The above numerical framework is employed to predict soot particle formation in the Delft Adelaide flame III, which is a benchmark flame of the International Sooting Flame (ISF) workshop. The target flame is featured by low/high sooting propensity/intermittency and by relatively comprehensive flow/scalar/soot data available for validating the model framework. Simulation results are compared with the experimental results and discussed for both the gas phase and the particulate phase. A satisfactory quantitative agreement has been obtained especially in terms of soot volume fraction. The ability of the S-EQMOM to provide information on particle size distribution indicates a dominant unimodal distribution along the flame centerline

Soot Prediction in a Model Aero-Engine Combustor using a Quadrature-based Method of Moments

Numerical simulations of aero-engine combustors are extremely challenging due to the complex multiscale and multiphysics phenomena involved. Currently, reliable modeling and prediction of soot particle formation produced during incomplete hydrocarbon combustion is one of the major issues in combustion research. The next generation of gas turbines for more sustainable aircraft engines must meet strict limitations for soot particle mass and size distribution. Therefore, a comprehensive understanding of the processes leading to soot particle formation and its precise prediction in practical combustion systems is crucial. In this work, a recently developed detailed soot model, the Split-based Extended Quadrature Method of Moments (S-EQMOM), is applied to simulate a model aero-engine combustor, experimentally investigated by the German Aerospace Center (DLR). In previous studies, the S-EQMOM demonstrated good prediction capability in predicting soot particle oxidation, important to account for the reduction of soot particles. Here, the model is evaluated at elevated pressure conditions. Large eddy simulations are performed using flamelet-based tabulated chemistry with artificially thickened flame (ATF) approach coupled with the S-EQMOM. The simulation results are analyzed for both the gas phase and soot solid phase and compared with the experimental data. Velocity and temperature fields are well predicted. Soot formation is underestimated by the simulation, but qualitatively in good agreement with the experimental data