Assessment of subgrid dispersion models for large-eddy simulations of turbulent jet flows with dilute spray droplets

Angelilli, Lorenzo; Ciottoli, Pietro Paolo; Picano, Francesco; Valorani, Mauro; Im, Hong G.

doi:10.1063/5.0095138

Cited by 8 publications

(2 citation statements)

References 46 publications

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“…where F d is the aerodynamic drag force and F g is the gravity force, ṁevap 2)-( 4) are outside the scope of this work. Interested readers can find the details in [4,5,8,[25][26][27][28].…”

Section: Numerical Modelmentioning

confidence: 99%

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Analysis of droplet evaporation dynamics using computational singular perturbation and tangential stretching rate

Angelilli,

Galassi,

Ciottoli

et al. 2024

Preprint

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Computational singular perturbation (CSP) has been successfully used in the analysis of complex chemically reacting flows by systematically identifying the intrinsic timescales and slow invariant manifolds that capture the essential subprocesses driving the dynamics of the system. In this article, the analytical and computational framework is applied for the first time to analyze the Lagrangian droplets undergoing evaporation and dispersion in the surrounding gases. First, a rigorous mathematical formulation is derived to adapt the CSP tools into the droplet dynamics equations, including the formal definition of the tangential stretching rate (TSR) that represents the explosive/dissipative nature of the system. A steady ammonia and a falling water droplet studies are then conducted to demonstrate the utility of the CSP methodology in identifying various physical mechanisms driving the evolution of the system, such as the distinction of thermal-driven and mass-driven regimes. Various definitions of the importance indices are also examined to provide in-depth analysis of different subprocesses and their interactions in modifying the droplet dynamics.

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Section: Numerical Modelmentioning

confidence: 99%

“…An accurate description of the fundamental characteristics of break-up, dispersion, and evaporation is essential for designing effective combustion systems. Such a high-fidelity spray model can improve the fidelity of engineering simulations in the Reynolds-average Navier-Stokes (RANS) [4,5] or large eddy simulations (LES) [6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

Analysis of droplet evaporation dynamics using computational singular perturbation and tangential stretching rate

Angelilli,

Galassi,

Ciottoli

et al. 2024

Preprint

Self Cite

View full text Add to dashboard Cite

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Effects of liquid properties on atomization and spray characteristics studied by planar two-photon fluorescence

et al. 2022

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In this work, planar two-photon laser-induced fluorescence (2p-LIF) is applied for the first time to analyze the fluid dependent spray structure and atomization behavior of water and ethanol in a quantitative way. A commercial six-hole DISI (Direct-Injection Spark-Ignition) injector was studied at different injection pressures, operated with liquids containing the LIF dye fluorescein. Specifically for DISI-injectors, the fluid-dependent atomization is very complex and not fully understood due to the cavitating, turbulent nozzle flow that dominates the spray formation. Optical access and analysis of the near-nozzle spray are often challenging due to multiple light scattering in dense regions which is reduced by 2p-LIF measurements using a femtosecond laser. This allows high-contrast spray imaging close to the nozzle, resulting in an improved identification of single liquid structures of the spray. Thus, a higher accuracy of sizing is possible. Compared to water, the ethanol spray shape shows increased cone angles in the nozzle near-field of about 6%, which cannot be explained by classical atomization theory based on aerodynamic breakup. The larger cone angle of ethanol was attributed to its larger viscosity, which could decelerate the flow at the wall of the injection hole, affecting the velocity profile of the emerging jet. The atomization shows a main jet breakup distance of 7–10 mm in which the structure sizes decreased drastically, specifically for water. For the size of the liquid structures in the near-nozzle region, which show dimensions of about 80–130 μm, ethanol exhibited about 2% smaller Feret's diameters than water for the tested time steps at 20 MPa. This effect is even more distinct for other injection pressures and positions at a further distance to the injector. For all investigated conditions and measurement positions downstream of the nozzle, ethanol showed on average about 24% smaller structures compared to the water spray. Although this trend is in accordance with the classical atomization theory based on the aerodynamic breakup mechanism, other effects, such as cavitation and nozzle-flow induced breakup, contribute to this behavior.

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A mesoscale bubble-induced turbulence model and simulation of gas–liquid flows

2023

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In gas-liquid two-phase flows, bubble motion significantly affects liquid-phase turbulence, and adding bubble-induced turbulence (BIT) source term is widely used to improve the simulation accuracy. This paper presented a new BIT model based on the energy-minimization multi-scale (EMMS) methodology. The model was constructed by considering two mesoscale factors, i.e., the sub-grid structures through analyzing the slip velocity and the gas holdup gradient, and the equivalent diameter of turbulent eddies calculated by the EMMS-based turbulence model. In order to verify its performance, the model was incorporated to the Eulerian-Lagrangian simulating framework and applied to two typical experimental systems. Both mean flow characteristics and turbulence quantities were well predicted, and the new model showed advantages over traditional BIT models, especially at higher gas velocities. Moreover, a strategy for counting energy dissipation in the simulation was devised and performed, whereby the dual effects of promotion and suppression on liquid-phase turbulence by bubbles can be reflected. The simulations demonstrated that BIT dominated the energy dissipation and turbulence was enhanced by BIT at higher gas velocities, while shear-induced turbulence (SIT) dominated the energy dissipation and turbulence is reduced due to the suppression by bubbles at lower gas velocities.

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Assessment of subgrid dispersion models for large-eddy simulations of turbulent jet flows with dilute spray droplets

Cited by 8 publications

References 46 publications

Analysis of droplet evaporation dynamics using computational singular perturbation and tangential stretching rate

Analysis of droplet evaporation dynamics using computational singular perturbation and tangential stretching rate

Effects of liquid properties on atomization and spray characteristics studied by planar two-photon fluorescence

A mesoscale bubble-induced turbulence model and simulation of gas–liquid flows

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