Publications
84 results found
Pesmazoglou I, Kempf A, Navarro-Martinez S, 2017, Large eddy simulation of particle aggregation in turbulent jets, Journal of Aerosol Science, Vol: 111, Pages: 1-17, ISSN: 0021-8502
Aggregation is an inter-particle process that involves a multitude of different physical and chemical mechanisms. Aggregation processes often occur within turbulent flows; for example in spray drying, soot formation, or nanoparticle formation. When the concentration of particles is very large, a direct simulation of individual particles is not possible and alternative approaches are needed. The present work follows the stochastic aggregation modelling based on a Lagrangian framework by Pesmazoglou, Kempf, and Navarro-Martinez (2016) and implements it in the Large Eddy Simulation context. The new coupled model is used to investigate particle aggregation in turbulent jets. Two cases are considered: an existent Direct Numerical Simulation of nanoparticle agglomeration in a planar jet and an experimental configuration of nanoparticles in a round jet. The results show a good agreement in both cases, demonstrating the advantages of the Lagrangian framework to model agglomeration and it capacity to describe the full particle size distribution.
Noh D, Gallot Lavallee S, Jones WP, et al., 2017, Validation of droplet evaporation models for a polydisperse spray in a non-swirling jet flame, European Combustion Meeting 2017, Publisher: Combustion Institute
The present work aims to deliver a numerical investigation of the turbulent spray jet flame in the context of LargeEddy Simulation. Several droplet evaporation models are studied in order to confirm their predictive capabilities interms of the time-averaged droplet temperature in the two-phase reactive flow. All the models under considerationare found to capture the formation of a double reaction zone flame and the measured lift-off height within a goodlevel of accuracy. However, the simulated wet-bulb temperature in the hot burnt gas between the two reaction zonesis considerably higher in comparison to measurements. This large discrepancy thus requires a further investigation inthe evaporation modelling.
Gallot Lavallee S, Noh D, Jones WP, et al., 2017, Experimental and numerical study of turbulent flame structures of a spray jet flame, European Combustion Meeting, Publisher: Combustion Institute
The flame structure of a laboratory scale n-heptane spray flame is investigated experimentally and numerically. Theexperimental burner is an open chamber with an ambient temperature co-flow surrounding a hollow cone simplexatomiser. OH-PLIF measurements are performed to study the interaction between turbulence, droplets, and chemistry.The simulation is performed using a Large Eddy Simulation with combustion modelling included by means of thesolution of the transport of the joint-sgsprobability density function using the stochastic fields method with promisingresults.
Franchetti BM, Cavallo Marincola F, Navarro-Martinez S, et al., 2016, Large Eddy Simulation of a 100 kWth swirling oxy-coal furnace, Fuel, Vol: 181, Pages: 491-502, ISSN: 1873-7153
Large Eddy Simulation (LES) has been applied to the swirling 100 kWth OXYCOAL-AC test facility of Aachen University. A set of models to represent devolatilisation, volatile combustion, char combustion and radiation for oxy-coal combustion in an LES framework has been implemented and tested. A qualitative analysis of the flow behaviour and the overall coal combustion processes occurring within the furnace was made. The LES results for the flow field were compared to axial and tangential mean velocity measurements, showing good agreement, particularly in the upstream regions of the flame. The LES results were also compared to oxygen concentrations (vol.) and gas temperature. Overall good agreement was observed in the upstream central regions of the flame, whilst downstream the LES overestimated the combustion rates. It was also found that the recirculation zones are sensitive to char combustion, not just to the rate of devolatilisation as one might expect. An interesting problem occured in the prediction of the velocity profiles, for which the measurements were taken based on coal-particles, so that the outer-most stream remained invisible in the experiments (but not the LES), due to being free from particles. The results show the potential of using LES for more complex oxy-coal combustion burners and opens the way for applications to industrial furnaces.
Pesmazoglou I, Kempf AM, Navarro-Martinez S, 2015, Stochastic modelling of particle aggregation, International Journal of Multiphase Flow, Vol: 80, Pages: 118-130, ISSN: 0301-9322
Aggregation is an inter-particle process which involves a multitude of different physicochemical mechanisms. In the present work, particles in the nano-scale are considered, with such concentration that renders their direct simulation as individual particles intractable. A stochastic aggregation model is presented for large particle populations in a Lagrangian framework. The model allows for simultaneous collisions between numerical parcels present in a certain volume of interaction (e.g. computational cell) and can be directly coupled to an unsteady numerical solver of a continuous flow. The model performance is evaluated against analytic solutions for a sum (Golovin) and constant aggregation kernel.
Vogiatzaki K, Navarro-Martinez S, De S, et al., 2015, Mixing Modelling Framework Based on Multiple Mapping Conditioning for the Prediction of Turbulent Flame Extinction, FLOW TURBULENCE AND COMBUSTION, Vol: 95, Pages: 501-517, ISSN: 1386-6184
Bulat G, Jones WP, Navarro-Martinez S, 2015, Large eddy simulations of isothermal confined swirling flow in an industrial gas-turbine, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 51, Pages: 50-64, ISSN: 0142-727X
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- Citations: 37
Dodoulas IA, Navarro-Martinez S, 2015, Analysis of extinction in a non-premixed turbulent flame using large eddy simulation and the chemical explosion mode analysis, COMBUSTION THEORY AND MODELLING, Vol: 19, Pages: 107-129, ISSN: 1364-7830
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- Citations: 17
Dimela N, Navarro-Martinez S, 2015, Surface density evolution in liquid break-up
Multiphase fluid flows, such as sprays and liquid jets, are common processes in Internal Combustion and Gas Turbine engines. Liquid fuel is injected into the combustion chamber and “atomises” into droplets, due to capillary and aerodynamic interactions of the liquid and the surrounding gas. The complete characterization of Atomization at realistic Reynolds and Weber numbers is not possible due to the wide range of scales (from mm to microns) and the need to define a “minimum” computational mesh size that captures the smallest liquid scales. The alternative is to “model” the effects of unresolved scales of liquid-breakup. One approach is to represent the Atomization process through the generation and destruction of the Surface Density (Σ-Y and ELSA methods). In order to capture the surface density precisely, both accuracy and mass conservation of the numerical scheme are crucial. A common approach is the coupling of Volume of Fluid with Level Set in CLSVOF, to ensure both improved surface representation and mass conservation. The present work focuses on the numerical study of surface density evolution in simple planar configurations (planar jets). The results show surface density evolution at different momentum ratios: from lower values, characteristic of diesel injectors, to high values, typical of air-blast atomizers in gas turbines. The simulations show the strong correlation between surface density and the formation of ligaments in primary atomization.
Yu S, Navarro-Martinez S, 2015, Modelling of deflagration to detonation transition using flame thickening, Proceedings of the Combustion Institute, Vol: 35, Pages: 1955-1961, ISSN: 0082-0784
This paper presents a new model to capture deflagration to detonation transition using a flame thickening approach. Two approaches have been implemented. One, where the thickening is applied to the reactive scalar only and other where all equations are transformed. A flame sensor is used to maintain the transformation close to the flame. The results show that detonation can be captured with relatively coarse meshes and dynamic choice of the thickening factor.
Alzwayi AS, Paul MC, Navarro-Martinez S, 2014, Large eddy simulation of transition of free convection flow over an inclined upward facing heated plate, INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER, Vol: 57, Pages: 330-340, ISSN: 0735-1933
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- Citations: 10
Pesmazoglou I, Kempf AM, Navarro-Martinez S, 2014, Aerosol nucleation in a turbulent jet using Large Eddy Simulations, CHEMICAL ENGINEERING SCIENCE, Vol: 116, Pages: 383-397, ISSN: 0009-2509
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- Citations: 7
Navarro-Martinez S, 2014, Large eddy simulation of spray atomization with a probability density function method, International Journal of Multiphase Flow, Vol: 63, Pages: 11-22, ISSN: 0301-9322
Despite recent advances in numerical methods for multiphase flows, the complete simulation of a liquid spray is still an illusive goal. There are few models that can describe accurately both the primary and secondary atomization simultaneously. The biggest difficulty is the wide range of length scales involved; from millimetres in the largest liquid structures close to the smallest micron-size droplets. This wide range makes Direct Numerical Simulation of sprays very expensive all scales need to be resolved and expensive algorithms are required to reconstruct accurately the interface. Large eddy simulations are becoming increasingly popular in turbulent flows due to their better description of turbulence and the relative robustness of sub-grid stress models. Despite its advantages, large eddy simulation cannot describe accurately fluid structures that occur at sub-grid levels. This paper presents a new model to describe the atomization process. The method consist of solving a joint sub-grid probability density function of liquid volume and surface using stochastic methods. The approach can simulate both dense and dilute regions of the spray. The proposed model can determine instantaneous sub-grid liquid structures (droplets) distributions as well as to capture the primary break-up. The results of the simulations are compared to a Direct Numerical Simulation of a Diesel Jet break-up. The mean liquid volume and surface density are well predicted; The modelling of the sub-grid scales is shown to be fundamental in the dilute regions of the spray.
Chalmers H, Al-Jeboori M, Anthony B, et al., 2014, OxyCAP UK: Oxyfuel Combustion - Academic Programme for the UK, 12th International Conference on Greenhouse Gas Control Technologies (GHGT), Publisher: ELSEVIER SCIENCE BV, Pages: 504-510, ISSN: 1876-6102
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- Citations: 1
Pesmazoglou I, Kempf AM, Navarro-Martinez S, 2013, A dynamic model for the Lagrangian stochastic dispersion coefficient, PHYSICS OF FLUIDS, Vol: 25, ISSN: 1070-6631
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- Citations: 9
Prasad VN, Masri AR, Navarro-Martinez S, et al., 2013, Investigation of auto-ignition in turbulent methanol spray flames using Large Eddy Simulation, COMBUSTION AND FLAME, Vol: 160, Pages: 2941-2954, ISSN: 0010-2180
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- Citations: 30
Dodoulas IA, Navarro-Martinez S, 2013, Large Eddy Simulation of Premixed Turbulent Flames Using the Probability Density Function Approach, FLOW TURBULENCE AND COMBUSTION, Vol: 90, Pages: 645-678, ISSN: 1386-6184
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- Citations: 34
Franchetti BM, Marincola FC, Navarro-Martinez S, et al., 2013, Large Eddy simulation of a pulverised coal jet flame, PROCEEDINGS OF THE COMBUSTION INSTITUTE, Vol: 34, Pages: 2419-2426, ISSN: 1540-7489
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- Citations: 102
Zoby MRG, Kronenburg A, Navarro-Martinez S, et al., 2012, Assessment of conventional droplet evaporation models for spray flames, High Performance Computing in Science and Engineering 2011 - Transactions of the High Performance Computing Center, Stuttgart, HLRS 2011, Pages: 209-227
The present work investigates droplet evaporation rates in inert and reactive environments using fully resolved Direct Numerical Simulation (DNS). The droplets are arranged in regular droplet layers and the evaporation of two different fuels, n-heptane and kerosene, is investigated under engine like conditions. It is found that the performance of standard models fort he evaporation rate strongly depends on the modelling of the representative properties. The conventional 1/3-rule for their computation does not necessarily lead to good agreement between model and DNS. This holds for droplet evaporation in non-reacting and reacting environments. Conditions at the droplet surface would need to be more heavily weighted for better model performance. The droplet loading has a minor effect on the validity of the standard single droplet evaporation models. © Springer-Verlag Berlin Heidelberg 2012.
Jones WP, Lettieri C, Marquis AJ, et al., 2012, Large Eddy Simulation of the two-phase flow in an experimental swirl-stabilized burner, 8th International Symposium on Engineering Turbulence Modelling and Measurements
Jones WP, Lyra S, Navarro-Martinez S, 2012, Large Eddy Simulation of Turbulent Confined Highly Swirling Annular Flows, FLOW TURBULENCE AND COMBUSTION, Vol: 89, Pages: 361-384, ISSN: 1386-6184
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- Citations: 9
Jones WP, Lyra S, Navarro-Martinez S, 2012, Numerical investigation of swirling kerosene spray flames using Large Eddy Simulation, COMBUSTION AND FLAME, Vol: 159, Pages: 1539-1561, ISSN: 0010-2180
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- Citations: 52
Zoby MRG, Kronenburg A, Navarro-Martinez S, et al., 2012, Assessment of conventional droplet evaporation models for spray flames, Pages: 209-227, ISBN: 9783642238680
The present work investigates droplet evaporation rates in inert and reactive environments using fully resolved Direct Numerical Simulation (DNS). The droplets are arranged in regular droplet layers and the evaporation of two different fuels, n-heptane and kerosene, is investigated under engine like conditions. It is found that the performance of standard models fort he evaporation rate strongly depends on the modelling of the representative properties. The conventional 1/3-rule for their computation does not necessarily lead to good agreement between model and DNS. This holds for droplet evaporation in non-reacting and reacting environments. Conditions at the droplet surface would need to be more heavily weighted for better model performance. The droplet loading has a minor effect on the validity of the standard single droplet evaporation models. © Springer-Verlag Berlin Heidelberg 2012.
Navarro-Martinez S, Rigopoulos S, 2011, Differential Diffusion modelling in LES with RCCE-reduced chemistry
Navarro-Martinez S, Kronenburg A, 2011, Flame Stabilization Mechanisms in Lifted Flames, FLOW TURBULENCE AND COMBUSTION, Vol: 87, Pages: 377-406, ISSN: 1386-6184
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- Citations: 55
Navarro-Martinez S, Rigopoulos S, 2011, Large Eddy Simulation of a Turbulent Lifted Flame using Conditional Moment Closure and Rate-Controlled Constrained Equilibrium, FLOW TURBULENCE AND COMBUSTION, Vol: 87, Pages: 407-423, ISSN: 1386-6184
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- Citations: 16
Zoby MRG, Navarro-Martinez S, Kronenburg A, et al., 2011, Turbulent mixing in three-dimensional droplet arrays, INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW, Vol: 32, Pages: 499-509, ISSN: 0142-727X
The atomisation, evaporation and subsequent mixing of fuel from a liquid spray determines the effectiveness of the combustion processes in gas turbines and internal combustion engines. In the present paper, three-dimensional direct numerical simulations (DNS) of the evaporation of methanol droplets in hot environments are presented. The gas phase mixing is assessed by examining the scalar dissipation and the mixture fraction probability density function (PDF). Novel multi-conditional models are proposed that use mixture fraction and structural parameters as the conditioning variables for the scalar dissipation which is found to be well predicted in terms of magnitude and distribution. The beta-PDF description of the mixture fraction seems to capture well the global behaviour for a laminar environment and for time-averaged results in turbulent cases. A novel model for the mixture fraction PDF is also proposed based on the multi-conditional model for scalar dissipation and an accurate representation of the PDF is achieved. (C) 2011 Elsevier Inc. All rights reserved.
Kronenburg A, Zoby MRG, Navarro-Martinez S, et al., 2011, Scalar mixing in droplet arrays in stagnant and convective environments, High Performance Computing in Science and Engineering 2010 - Transactions of the High Performance Computing Center, Stuttgart, HLRS 2010, Pages: 191-202
Droplet evaporation is usually modelled as a subgrid process and induces local inhomogeneities in the mixture fraction probability density function (PDF) and its scalar dissipation. These inhomogeneities are usually neglected, however, they can be significant and determine the combustion regime. In the present work, Direct Numerical Simulations (DNS) of fully resolved evaporating methanol droplets are analysed, assessing fuel vapour mixing in laminar and turbulent flows. The results show that scalar probability distributions and scalar dissipation vary greatly depending on the position relative to the droplet position, on droplet loading and on flow conditions. The β-PDF seems to capture the global behaviour for laminar flows around droplet arrays with low droplet density, however, mixing characteristics for higher droplet densities in stagnant and turbulent flows cannot be approximated by a β-PDF, and modelling approaches based on cell mean values will lead to erroneous results. © Springer-Verlag Berlin Heidelberg 2011.
Vogiatzaki K, Kronenburg A, Navarro-Martinez S, et al., 2011, Stochastic multiple mapping conditioning for a piloted, turbulent jet diffusion flame, PROCEEDINGS OF THE COMBUSTION INSTITUTE, Vol: 33, Pages: 1523-1531, ISSN: 1540-7489
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- Citations: 22
Kronenburg A, Zoby MRG, Navarro-Martinez S, et al., 2011, Scalar Mixing in Droplet Arrays in Stagnant and Convective Environments, 14th Annual Results and Review Workshop on High Performance Computing in Science and Engineering, Publisher: SPRINGER-VERLAG BERLIN, Pages: 191-+
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