Large-eddy simulation of droplet-laden cough jets with a realistic manikin model

2021 ◽  
pp. 1420326X2110322
Author(s):  
Haiwen Ge ◽  
Liang Chen ◽  
Chunwen Xu ◽  
Xinguang Cui
Keyword(s):  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Fluid Dynamic ◽  
Geometric Model ◽  
Mouth Opening ◽  
Droplet Breakup ◽  
Inlet Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Droplet Penetration

Three-dimensional computational fluid dynamic (CFD) methods were used to simulate a cough jet that contains droplets. The turbulent cough flow is modelled using large-eddy simulation with a dynamic structure model. An Eulerian–Lagrangian approach was adopted to model the two-phase flows. Droplet breakup, evaporation, dispersion and drag forces were considered in the model. Two different inlet velocity profiles, which are based on constant mouth opening area and variable mouth opening area, were considered in the CFD model. The numerical model was validated by comparing with the available experimental measurements. The results show that the use of the fixed mouth opening area in the geometric model shows the inlet velocity profile of the ‘variable area’ matched better with the experimental data than with the ‘constant area’ inlet velocity profile. Droplet dynamics were analysed with a focus on the droplet penetration and droplet distribution in space during the whole coughing process. The droplet penetration shows two-stage profiles, both of which can be described by logarithmic functions. This is consistent with the analytical results of the simplified drag model. The droplets generated during the mouth opening or closing periods have a higher velocity and longer droplet penetration. With a higher room temperature, the droplet penetration is shorter.

Large Eddy Simulation of Forced and Unforced Plane Jets Impinging on a Convex Surface

2014 ◽  
Author(s):  
N. Kharoua ◽  
L. Khezzar ◽  
Z. Nemouchi ◽  
M. AlShehhi
Keyword(s):  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Axial Velocity ◽  
Velocity Profiles ◽  
Impinging Jets ◽  
Inlet Velocity ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Target Wall ◽  
The Mean

Large Eddy Simulation study of plane impinging jets with different inlet velocity profiles was conducted. The inlet velocity profile was forced at a frequency equal to 600Hz and amplitude equal to 30% of the mean inlet velocity. The Reynold number, based on the jet width W and the inlet velocity, is equal to 5600. The distance of the jet exit from the target wall was varied from 2W to 10W to cover different types of impinging jets with different flow structures. The time-averaged Nusselt Number Nu profiles, along the curved wall, are characterized by two peaks for the shortest distance 2W and only one peak, at the impingement region, for the largest distance 10W. The first peak, at the impingement region is investigated through profiles of the mean axial velocity, the rms axial velocity, the mean static pressure, and the mean static temperature plotted on the jet centerline. For the second peak of the Nu (2W case), the turbulence level and the thickness of the highly turbulent layer near the curved wall were depicted on curved lines parallel and very close to the target wall. Forcing the considered jets at 600Hz was found to reduce the Nu while a fully developed inlet velocity profile causes an important increase of the Nu at the impingement region compared with flat inlet velocity profiles.

scholarly journals Towards Massively Parallel Large Eddy Simulation of Turbine Stages

2013 ◽  
Author(s):  
Gaofeng Wang ◽  
Dimitrios Papadogiannis ◽  
Florent Duchaine ◽  
Nicolas Gourdain ◽  
Laurent Y. M. Gicquel
Keyword(s):  
Experimental Data ◽  
Large Eddy Simulation ◽  
Gas Turbine ◽  
High Performance ◽  
Fluid Dynamic ◽  
Rotor Blades ◽  
Massively Parallel ◽  
High Fidelity ◽  
Eddy Simulation ◽  
Large Eddy

The context of integrated numerical simulations of gas turbine engines by use of high-fidelity Computational Fluid Dynamic (CFD) tools recently emerged as a promising path to improve engines design and understanding. Relying on massively parallel super-computing such propositions still have to prove feasibility to efficiently take advantage of the ever increasing computing power made available worldwide. Although Large Eddy Simulation (LES) has recently proven its superiority in the context of the combustion chamber of gas turbine, methodologies need to be developed and start addressing the problem of the turbomachinery stages, if integrated simulations based on LES are to be foreseen. In the proposed work an in-house code and strategy, called TurboAVBP, is developed for turbomachinery LES thanks to the coupling of multi-copies of the unstructured compressible reacting LES solver AVBP, designed to run efficiently on high performance massively parallel architectures. Aside from the specificity of such wall bounded flows, rotor/stator LES type simulations require specific attention and the interface should not interfere with the numeric scheme to preserve proper representation of the unsteady physics crossing this interface. A tentative LES compliant solution based on moving overset grids method is proposed and evaluated in this work for high-fidelity simulation of the rotor/stator interactions. Simple test cases of increasing difficulty with reference numerical are detailed and prove the solution in handling acoustics, vortices and turbulence. The approach is then applied to the QinetiQ MT1 high-pressure transonic turbine for comparison with experimental data. Two configurations are computed: the first one is composed of 1 scaled stator section and 2 rotors while the second computation considers the geometrically accurate periodic quarter of the machine, i.e. 8 stators and 15 rotors to test scalability issues of such applications. Although under-resolved, the LES pressure profiles on the stator and rotor blades appear to be in good agreement with experimental data and are quite competitive compared to the traditional (Unsteady) Reynolds-Averaged Navier-Stokes (RANS or URANS) modeling approach. Unsteady features inherently present in these LES underline the complexity of the flow in a turbine stage and clearly demand additional diagnostics to be properly validated.

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 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 Turbulent Mixing of a Jet in Cross-Flow

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Mostafa Esmaeili ◽  
Asghar Afshari ◽  
Farhad A. Jaberi
Keyword(s):  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Turbulent Mixing ◽  
Mass Density ◽  
Cross Flow ◽  
Vortex Pair ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Jet In Cross Flow ◽  
Large Eddy

An Eulerian–Lagrangian mathematical/computational methodology is employed for large-eddy simulation (LES) and detailed study of turbulent mixing in jet in cross-flow (JICF) configuration. Accurate prediction of mixing in JICF is crucially important to the development of advanced combustion systems. A high-order multiblock finite difference (FD) computational algorithm is used to solve the Eulerian velocity and pressure equations in a generalized coordinate system. The composition field, describing the mixing, is obtained from the filtered mass density function (FMDF) and its stochastic Lagrangian Monte-Carlo (MC) solver. Our simulations are shown to accurately predict the important flow features present in JICF such as the counter-rotating vortex pair (CVP), horseshoe, shear layer, and wake vortices. The consistency of the FD and MC parts of the hybrid LES/FMDF model is established for the simulated JICF in various conditions, indicating the numerical accuracy of the model. The effects of parameters influencing the jet penetration, entrainment, and turbulent mixing such as the jet velocity profile, and jet pulsation are investigated. The results show that the jet exit velocity profile significantly changes the trajectory and mixing of injected fluid. The jet pulsation is also shown to enhance the mixing depending on the flow Strouhal number. The LES/FMDF results are shown to be in good agreement with the available experimental data, confirming the reliability of LES/FMDF method for numerical simulation of turbulent mixing in complex flow configurations.

An Anisotropic Subgrid Model for Large Eddy Simulation of Wall Bounded Turbulent Flows

2007 ◽  
Author(s):  
Sachin S. Badarayani ◽  
Kyle D. Squires
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Velocity Profile ◽  
Turbulent Flows ◽  
Model Parameters ◽  
Wall Region ◽  
Outer Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Near Wall

Large Eddy Simulation (LES) of high-Reynolds-number wall-bounded turbulent flows is prohibitively expensive if the energy-containing eddies in the near-wall region are resolved. This motivates the use of wall-layer models in which an approximate solution of the near wall dynamics is bridged to an LES of the outer flow. The main interest of the present work are wall-modeling strategies based on Detached Eddy Simulation (DES). In these approaches, the near-wall solution is closed using a Reynolds-averaged Navier Stokes model with a subgrid closure applied to the outer flow. As is well known, the original DES formulation applied directly as a wall model results in a shift in the velocity profile, corresponding to an under-estimation of the skin friction. A new formulation is proposed in this contribution in which the wall-parallel components of the modeled stress are reduced in order to lower the influence of the model and increase the resolved stress. The effectiveness of the new model is evaluated via comparison against DES predictions using the original and recently-proposed versions of the method. The effect of grid resolution and model parameters are also assessed using computations of turbulent channel flow at a Reynolds number based on friction velocity and channel halfwidth of 5000. The predictions show that the anisotropic form of the model stress yields an improved prediction of the mean velocity profile in better agreement with the logarithmic law and with larger resolved stress in the near-wall region.

scholarly journals A population balance model for large eddy simulation of polydisperse droplet evolution

2019 ◽  
Vol 878 ◽  
pp. 700-739 ◽  
Author(s):  
A. K. Aiyer ◽  
D. Yang ◽  
M. Chamecki ◽  
C. Meneveau
Keyword(s):  
Large Eddy Simulation ◽  
Size Distribution ◽  
Droplet Size ◽  
Droplet Breakup ◽  
Dispersed Phase ◽  
Size Distributions ◽  
Oil Droplets ◽  
One Dimensional ◽  
Eddy Simulation ◽  
Large Eddy

In the context of many applications of turbulent multi-phase flows, knowledge of the dispersed phase size distribution and its evolution is critical to predicting important macroscopic features. We develop a large eddy simulation (LES) model that can predict the turbulent transport and evolution of size distributions, for a specific subset of applications in which the dispersed phase can be assumed to consist of spherical droplets, and occurring at low volume fraction. We use a population dynamics model for polydisperse droplet distributions specifically adapted to a LES framework including a model for droplet breakup due to turbulence, neglecting coalescence consistent with the assumed small dispersed phase volume fractions. We model the number density fields using an Eulerian approach for each bin of the discretized droplet size distribution. Following earlier methods used in the Reynolds-averaged Navier–Stokes framework, the droplet breakup due to turbulent fluctuations is modelled by treating droplet–eddy collisions as in kinetic theory of gases. Existing models assume the scale of droplet–eddy collision to be in the inertial range of turbulence. In order to also model smaller droplets comparable to or smaller than the Kolmogorov scale we extend the breakup kernels using a structure function model that smoothly transitions from the inertial to the viscous range. The model includes a dimensionless coefficient that is fitted by comparing predictions in a one-dimensional version of the model with a laboratory experiment of oil droplet breakup below breaking waves. After initial comparisons of the one-dimensional model to measurements of oil droplets in an axisymmetric jet, it is then applied in a three-dimensional LES of a jet in cross-flow with large oil droplets of a single size being released at the source of the jet. We model the concentration fields using $N_{d}=15$ bins of discrete droplet sizes and solve scalar transport equations for each bin. The resulting droplet size distributions are compared with published experimental data, and good agreement for the relative size distribution is obtained. The LES results also enable us to quantify size distribution variability. We find that the probability distribution functions of key quantities such as the total surface area and the Sauter mean diameter of oil droplets are highly variable, some displaying strong non-Gaussian intermittent behaviour.

scholarly journals Cloud Cavitating Flow Over a Submerged Axisymmetric Projectile and Comparison Between Two-Dimensional RANS and Three-Dimensional Large-Eddy Simulation Methods

2016 ◽  
Vol 138 (6) ◽  
Author(s):  
Yiwei Wang ◽  
Chenguang Huang ◽  
Xin Fang ◽  
Xianian Yu ◽  
Xiaocui Wu ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Cavitating Flow ◽  
Two Dimensional ◽  
Cloud Cavitation ◽  
Cavity Collapse ◽  
Eddy Simulation ◽  
2D Simulation ◽  
Large Eddy

For the cloud cavitation around slender axisymmetric projectiles, a two-dimensional (2D) numerical method was based on the mixture approach with Singhal cavitation model and modified renormalization-group (RNG) k–ε turbulence model, and a three-dimensional (3D) method was established with large-eddy simulation (LES) and volume of fraction (VOF) approach. The commercial computational fluid dynamic (CFD) software fluent is used for the 2D simulation, and the open source code OpenFOAM is adopted for the 3D calculation. Experimental and numerical results were presented on a typical case, in which the projectile moves with a quasi-constant axial speed. Simulation results agree well with experimental results. An analysis of the evolution of cavitating flow was performed, and the related physical mechanism was discussed. Results demonstrate that shedding cavity collapse plays an important role in the generation and acceleration of re-entry jet, which is the main reason for the instability of cloud cavitation. The 2D Reynolds-Averaged Navier–Stokes (RANS) method can represent the physical phenomena effectively. The 3D LES method can give an efficient simulation on the shedding vortices, and considerable accurate shapes of shedding cavities are captured.

Sign in / Sign up

Export Citation Format

Share Document