scholarly journals Large-Eddy Simulation of ECN Spray A: Sensitivity Study on Modeling Assumptions

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3360
Author(s):  
Mahmoud Gadalla ◽  
Jeevananthan Kannan ◽  
Bulut Tekgül ◽  
Shervin Karimkashi ◽  
Ossi Kaario ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Sensitivity Study ◽  
Droplet Breakup ◽  
Injection Volume ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Subgrid Scales ◽  
Secondary Breakup ◽  
Breakup Model ◽  
Model Approach

In this study, various mixing and evaporation modeling assumptions typically considered for large-eddy simulation (LES) of the well-established Engine Combustion Network (ECN) Spray A are explored. A coupling between LES and Lagrangian particle tracking (LPT) is employed to simulate liquid n-dodecane spray injection into hot inert gaseous environment, wherein Lagrangian droplets are introduced from a small cylindrical injection volume while larger length scales within the nozzle diameter are resolved. This LES/LPT approach involves various modeling assumptions concerning the unresolved near-nozzle region, droplet breakup, and LES subgrid scales (SGS) in which their impact on common spray metrics is usually left unexplored despite frequent utilization. Here, multi-parametric analysis is performed on the effects of (i) cylindrical injection volume dimensions, (ii) secondary breakup model, particularly Kelvin–Helmholtz Rayleigh–Taylor (KHRT) against a no-breakup model approach, and (iii) LES SGS models, particularly Smagorinsky and one-equation models against implicit LES. The analysis indicates the following findings: (i) global spray characteristics are sensitive to radial dimension of the cylindrical injection volume, (ii) the no-breakup model approach performs equally well, in terms of spray penetration and mixture formation, compared with KHRT, and (iii) the no-breakup model is generally insensitive to the chosen SGS model for the utilized grid resolution.

Large Eddy Simulation of the Wake Behind a Turning Ship

2002 ◽  
Author(s):  
Ibrahim Yavuz ◽  
Zeynep N. Cehreli ◽  
Ismail B. Celik ◽  
Shaoping Shi
Keyword(s):  
Large Eddy Simulation ◽  
Sensitivity Study ◽  
West Virginia University ◽  
Vortical Structures ◽  
Turbulence Structures ◽  
Eddy Simulation ◽  
Flow Generation ◽  
Large Eddy ◽  
Unsteady Inflow ◽  
Random Flow

This study examines the dynamics of turbulent flow in the wake of a turning ship using the large eddy simulation (LES) technique. LES is applied in conjunction with a random flow generation (RFG) technique originally developed at West Virginia University to provide unsteady inflow boundary conditions. As the ship is turning, the effects of the Coriolis and centrifugal forces on vortical structures are included. The effects of the Coriolis force on the flow-field are assessed and a grid sensitivity study is performed. The predicted turbulence structures are analyzed and compared with the wake of a non-turning ship.

scholarly journals Large eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey area ship track experiment

2015 ◽  
Vol 15 (10) ◽  
pp. 5851-5871 ◽  
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for 8 h (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of the cloud into mesoscale rolls. After 8 h, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In that case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

Large-Eddy Simulation of Atomizing Spray With Stochastic Modeling of Secondary Breakup

2003 ◽  
Author(s):  
Sourabh V. Apte ◽  
Mikhael Gorokhovski ◽  
Parviz Moin
Keyword(s):  
Large Eddy Simulation ◽  
Droplet Size ◽  
Particle Tracking ◽  
Hybrid Approach ◽  
Computational Cost ◽  
Fuel Injector ◽  
Combustion Dynamics ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Secondary Breakup

Large-eddy simulation (LES) of reacting multi-phase flows in practical combustor geometries is essential to accurately predict complex physical phenomena of turbulent mixing and combustion dynamics. This necessitates use of Lagrangian particle-tracking methodology for liquid phase in order to correctly capture the droplet evaporation rates in the sparse-liquid regime away from the fuel injector. Our goal in the present work is to develop a spray-atomization methodology which can be used in conjuction with the standard particle-tracking schemes and predict the droplet-size distribution accurately. The intricate process of primary atomization and lack of detailed experimental observations close to the injector requires us to model its global effects and focus on secondary breakup to capture the evolution of droplet sizes. Accordingly, a stochastic model for LES of atomizing spray is developed. Following Kolmogorov’s idea of viewing solid particle-breakup as a discrete random process, atomization of liquid blobs at high relative liquid-to-gas velocity is considered in the framework of uncorrelated breakup events, independent of the initial droplet size. Kolmogorov’s discrete model of breakup is represented by Fokker-Planck equation for the temporal and spatial evolution of droplet radius distribution. The parameters of the model are obtained dynamically by relating them to the local Weber number. A novel hybrid-approach involving tracking of individual droplets and a group of like-droplets known as parcels is developed to reduce the computational cost and maintain the essential features and dynamics of spray evolution. The present approach is shown to capture the complex fragmentary process of liquid atomization in idealized and realistic Diesel and gas-turbine combustors.

scholarly journals Large Eddy Simulation of an Ethanol Spray Flame with Secondary Droplet Breakup

2021 ◽  
Author(s):  
S. Gallot-Lavallée ◽  
W. P. Jones ◽  
A. J. Marquis
Keyword(s):  
Liquid Phase ◽  
Large Eddy Simulation ◽  
Droplet Size ◽  
Size Class ◽  
Droplet Breakup ◽  
Fuel Injector ◽  
Low Oxygen ◽  
Stochastic Field ◽  
Eddy Simulation ◽  
Large Eddy

AbstractA computational investigation of three configurations of the Delft Spray in Hot-diluted Co-flow (DSHC) is presented. The selected burner comprises a hollow cone pressure swirl atomiser, injecting an ethanol spray, located in the centre of a hot co-flow generator, with the conditions studied corresponding to Moderate or Intense Low-oxygen Dilution (MILD) combustion. The simulations are performed in the context of Large Eddy Simulation (LES) in combination with a transport equation for the joint probability density function (pdf) of the scalars, solved using the Eulerian stochastic field method. The liquid phase is simulated by the use of a Lagrangian point particle approach, where the sub-grid-scale interactions are modelled with a stochastic approach. Droplet breakup is represented by a simple primary breakup model in combination with a stochastic secondary breakup formulation. The approach requires only a minimal knowledge of the fuel injector and avoids the need to specify droplet size and velocity distributions at the injection point. The method produces satisfactory agreement with the experimental data and the velocity fields of the gas and liquid phase both averaged and ‘size-class by size-class’ are well depicted. Two widely accepted evaporation models, utilising a phase equilibrium assumption, are used to investigate the influence of evaporation on the evolution of the liquid phase and the effects on the flame. An analysis on the dynamics of stabilisation sheds light on the importance of droplet size in the three spray flames; different size droplets play different roles in the stabilisation of the flames.

scholarly journals Large-eddy simulation of ship tracks in the collapsed marine boundary layer: a case study from the Monterey Area Ship Track experiment

2014 ◽  
Vol 14 (17) ◽  
pp. 24387-24439
Author(s):  
A. H. Berner ◽  
C. S. Bretherton ◽  
R. Wood
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Liquid Water ◽  
Satellite Images ◽  
Sensitivity Study ◽  
Liquid Water Path ◽  
Water Path ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Ship Tracks

Abstract. For the first time, a large-eddy simulation (LES) coupled to a bulk aerosol scheme is used to simulate an aircraft-sampled ship track. The track was formed by the M/V Sanko Peace on 13 June 1994 in a shallow drizzling boundary layer with high winds but very low background aerosol concentrations (10 cm−3). A Lagrangian framework is used to simulate the evolution of a short segment of track as it is advected away from the ship for eight hours (a downwind distance exceeding 570 km). Using aircraft observations for initialization, good agreement is obtained between the simulated and observed features of the ambient boundary layer outside the track, including the organization of cloud into mesoscale rolls. After eight hours, a line of aerosol is injected to start the ship track. The simulation successfully reproduces the significant albedo enhancement and suppression of drizzle observed within the track. The aerosol concentration within the track dilutes as it broadens due to turbulent mixing. A sensitivity study shows the broadening rate strongly depends on the alignment between the track and the wind-aligned boundary layer rolls, as satellite images of ship tracks suggest. Entrainment is enhanced within the simulated track, but the observed 100 m elevation of the ship track above the surrounding layer is not simulated, possibly because the LES quickly sharpens the rather weak observed inversion. Liquid water path within the simulated track increases with time even as the ambient liquid water path is decreasing. The albedo increase in the track from liquid water and cloud fraction enhancement (second indirect effect) eventually exceeds that from cloud droplet number increases (first indirect or Twomey effect). In a sensitivity study with a higher initial ambient aerosol concentration, stronger ship track aerosol source, and much weaker drizzle, there is less liquid water inside the track than outside for several hours downwind, consistent with satellite estimates for such situations. In this case, the Twomey effect dominates throughout, although, as seen in satellite images, the albedo enhancement of the track is much smaller.

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