marco arienti - Academia.edu (original) (raw)

Papers by marco arienti

Physics of Fluids, 2009

New insight into the mechanism of liquid jet in crossflow atomization is provided by an analysis ... more New insight into the mechanism of liquid jet in crossflow atomization is provided by an analysis technique based on proper orthogonal decomposition and spectral analysis. Data are provided in the form of high-speed videos of the jet near field from experiments over a broad range of injection conditions. For each condition, proper orthogonal modes (POMs) are generated and ordered by intensity variation relative to the time average. The feasibility of jet dynamics reduction by truncation of the POM series to the first few modes is then examined as a function of crossflow velocity for laminar and turbulent liquid injection. At conditions where the jet breaks up into large chunks of liquid, the superposition of specific orthogonal modes is observed to track long waves traveling along the liquid column. The temporal coefficients of these modes can be described as a bandpass spectrum that shifts toward higher frequencies as the crossflow velocity is increased. The dynamic correlation of these modes is quantified by their cross-power spectrum density. Based on the frequency and wavelength extracted from the videos, the observed traveling waves are linked to the linearly fastest growing wave of Kelvin-Helmholtz instability. The gas boundary layer thickness at the gas-liquid shear layer emerges at the end of this study as the dominant length scale of jet dynamics at moderate Weber numbers.

Immiscible drop collision, as occurring in fuel-oxidizer sprays or in the release of certain fire... more Immiscible drop collision, as occurring in fuel-oxidizer sprays or in the release of certain fire-extinguishing agents, tends to exhibit a much richer behavior with respect to miscible drops collision thanks to the formation of a liquid-liquid interface during impact. For instance, in near-head-on diesel-water drop collisions, ``overlaying'' may occur in which the diesel oil flows from the collision point around the water drop to gather at the opposite location of the drop. To simulate this class of multi-material flows, the combined volume-of-fluid / level set methodology that sharply captures a single liquid-gas interface (Sussman et al, J. of Comp. Phys., 2007) needs to be duplicated for a second, independent interface. In this presentation, we will show that simulation results are not affected by the reconstruction order of the interfaces, as in other surface capturing methods. We will also propose different numerical solutions to treat surface tension in the triple point computational cells, and examine the characteristics of the flow developing at the contact line between the two liquids and air in overlaying head-on collisions.

Evolution of flow of immiscible fluids under high-shear poses severe challenges to the developmen... more Evolution of flow of immiscible fluids under high-shear poses severe challenges to the development of accurate and robust numerical techniques that can maintain a sharp separating interface. The implicit volume of fluid (VOF) advection using High Resolution Interface Capturing (HRIC) scheme offers the advantage of numerical stability at large time steps, but has been observed to cause interface diffusion at high shear. Advection using the standard Piecewise Linear Interface Calculation (PLIC), on the other hand, requires much smaller time steps. We have developed an efficient, accurate coupling approach between a sharp-interface front-tracking library and an unstructured-grid implicit flow solver. The high efficiency results from a localized searching algorithm for grid cells close to the interface. The accuracy is obtained from a conservative interfacial force transfer between front and grid that preserves momentum balance and from a novel approach for constructing the density profile across the interface. Validation of the method with tests of drop deformation in high shear will be presented, with attention to efficiency and accuracy. The performance of this stand-alone front-tracking capability on unstructured grids suggests that the coupled approach may be well suited for simulations in complex domains.

We propose two simple models for evaluating the role of diffusion in the shear layer behind the t... more We propose two simple models for evaluating the role of diffusion in the shear layer behind the triple point in the decaying portion of a detonation cell. Both models are based on an idealized detonation cell cycle, with imposed detonation speed profile. Following the standard triple-point analysis at the shock front, time-accurate integration of the species evolution is carried out using a detailed reaction mechanism and simplified models of mixing. The first model examined considers fast mixing of the fluid across the shear layer behind the triple point to map ignition enhancement as a function of mixture fraction. The second model is to treat the mixing layer as a one-dimensional, temporally-developing diffusion layer. Both model and simulations show that the effect of diffusion at the shear layer in the decaying portion of a detonation cell depends, as expected, on the activation energy of the reacting mixture. Negligible for regular detonation parameters, diffusion is found to significantly shorten the colder layer ignition delay in high-activation energy mixtures. Laminar flames are observed to emerge from the temporally developing shear layer in some cases.

The role played by the air stream in selecting the dominant wave mode in liquid jet in crossflow ... more The role played by the air stream in selecting the dominant wave mode in liquid jet in crossflow break-up is investigated in an experimental facility where a rectangular air jet is directed orthogonally toward the liquid column. The column is seen to immediately broaden upon impact of the air jet, with surface waves initiating along the windward surface. The ensuing break-up dynamics is captured by two synchronized high-speed cameras with identical lenses and orthogonal fields of view. The side view of the windward surface shows a wavelike structure whose peaks correspond, in the top view of the column, to transverse ligaments that increase in length with distance. The wave troughs correspond to thin sheets which distend, stretch, and eventually perforate into smaller droplets leaving behind the thicker transverse ligaments. The coherent structures of this complex dynamics are revealed by the simultaneous analysis of the two synchronized image sequences in a range of turbulent and non-turbulent flow conditions. Three-dimensional reconstruction aspects will be discussed, particularly how to identify the dominant wavelike modes that appear periodically in the video sequences.

Journal of Fluid Mechanics, 2005

An investigation of detonation diffraction through an abrupt area change has been carried out via... more An investigation of detonation diffraction through an abrupt area change has been carried out via a set of two-dimensional numerical simulations parameterized by the activation energy of the reactant. Our analysis is specialized to a reactive mixture with a perfect gas equation of state and a single-step reaction in the Arrhenius form. Lagrangian particles are injected into the flow as a diagnostic tool for identifying the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in the shock-based reference system. When simplified, this equation provides insight into the competition between the energy release rate and the expansion rate behind the diffracting front. The mechanism of spontaneous generation of transverse waves along the diffracting front is carefully analysed and related to the sensitivity of the reaction rate to temperature. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behaviour, super-, sub-and near-critical diffraction.

Atomizing liquids by injecting them into crossflows is a common approach to generate fuel sprays ... more Atomizing liquids by injecting them into crossflows is a common approach to generate fuel sprays in gas turbines and augmentors. The mechanisms by which the liquid jet initially breaks up, however, are not well understood. To analyze the instability mechanism of the liquid column, we perform proper orthogonal decomposition of side view images extracted from detailed simulations of the near injector primary atomization region. This analysis shows a single dominant wavelength with the associated interface corrugation traveling downstream with the jet. Using consistent temporal averaging of the simulation data we extract mean interface geometries and boundary layer velocity profiles. These are used to calculate the most unstable wavelength of the shear layer instability following the procedure of Boeck & Zaleski (2005). The theoretical wavelengths are comparable to those extracted from the simulation data. In addition to shear layer instability we analyze Rayleigh-Taylor as a potential instability mechanism of the liquid column.

Turbulent premixed combustion is present in many power generation and propulsion systems due to i... more Turbulent premixed combustion is present in many power generation and propulsion systems due to its large energy conversion rate (as compared to non-premixed combustion) and its potential for reduced emissions (at the lean limit). As a result, the study of turbulent premixed flames has received substantial attention in the past through experiment, analysis and simulation. In the recent past, unsteady Computational Fluid Dynamics (CFD) based models have been increasingly leveraged towards the in depth study of the physics of turbulent premixed flames. The bulk of this effort focuses on the response of the flame to turbulence. In contrast, we focus on the opposite problem, i.e. the modification of the turbulent flowfield by the flame. This topic has also received some attention but with a strong emphasis on planar (in the mean), flames propagating normal to the flow. Instead, we focus on flameholder-stabilized ducted flames, i.e. ones in which the flame is confined and substantially inclined to the incoming flow. The fundamental mechanisms by which the flame impacts the flow, i.e. dilatation, baroclinic vorticity generation and molecular diffusion enhancement are discussed in detail and their relative impact quantified. Limitations of modeling these mechanisms in current state of the art CFD models are also addressed.

Chemical Physics, 2011

The combination of short-range repulsive and long-range attractive forces in many-body dissipativ... more The combination of short-range repulsive and long-range attractive forces in many-body dissipative particle dynamics (MDPD) is examined at a vapor/liquid and liquid/solid interface. Based on the radial distribution of the virial pressure in a drop at equilibrium, a systematic study is carried out to characterize the sensitivity of the surface tension coefficient with respect to the inter-particle interaction parameters. For the first time, the approximately cubic dependence of the surface tension coefficient on the bulk density of the fluid is evidenced. In capillary flow, MDPD solutions are shown to satisfy the condition on the wavelength of an axial disturbance leading to the pinch-off of a cylindrical liquid thread; correctly, no pinch-off occurs below the cutoff wavelength. Moreover, in an example that illustrates the cascade of fluid dynamics behaviors from potential to inertial-viscous to stochastic flow, the dynamics of the jet radius is consistent with the power law predictions of asymptotic analysis. To model interaction with a solid wall, MDPD is augmented by a set of bell-shaped weight functions; hydrophilic and hydrophobic behaviors, including the occurrence of slip in the latter, are reproduced using a modification in the weight function that avoids particle clustering. The dynamics of droplets entering an inverted Y-shaped fracture junction is shown to be correctly captured in simulations parametrized by the Bond number, confirming the flexibility of MDPD in modeling interface-dominated flows.

Atomization of a liquid fuel jet by a high speed cross-flowing gas plays a critical role in many ... more Atomization of a liquid fuel jet by a high speed cross-flowing gas plays a critical role in many propulsion devices. High fidelity simulation offers the potential of a better understanding and enhancement of this atomization process. In this work, a computationally efficient hybrid Eulerian-Lagrangian approach is coupled with a droplet evaporation model and is used to probe the impact of evaporation on the spray development. The Coupled Level Set and Volume of Fluid (CLSVOF) method is used to directly calculate the breakup and coalescence of the liquid-gas interface. Adaptive Mesh Refinement (AMR) is adopted to achieve high resolution at the interface. Small fuel droplets in dilute regions are removed from the Eulerian description, transformed into Lagrangian particles and tracked by a discrete phase transport model. The coupling of the spray evaporation to the gas phase is examined with respect to jet blockage, spray penetration, and overall far-field spray dispersion. The calculation is validated with flow rate, spray size distribution and velocity data acquired in a spray rig at high-Weber, high-Reynolds number injection conditions. The effect of evaporation on spray distribution is also discussed.

Capillary pinch-off results carried out with the Many-Body Dissipative Particle Dynamics (MDPD) m... more Capillary pinch-off results carried out with the Many-Body Dissipative Particle Dynamics (MDPD) method are compared with the two-phase continuum discretization of hydrodynamics. The MDPD method provides a mesoscale description of the liquid-gas interface -- molecules can be thought of as grouped in particles with modeled Brownian and dissipative effects. No liquid-gas interface is explicitly defined; surface properties, such as surface tension, result from the MDPD interaction parameters. In side-to-side comparisons, the behavior of the MDPD liquid is demonstrated to replicate the macroscale behavior (thin interface assumption) calculated by the Combined Level Set-Volume of Fluid (CLSVOF) method. For instance, in both the continuum and mesoscale discretizations the most unstable wavelength perturbation leads to pinch-off, whereas a smaller wavelength-to-diameter ratio, as expected, does not. The behavior of the virial pressure in MDPD will be discussed in relation to the hydrodynamic capillary pressure that results from the thin interface assumption.

High-speed, high-resolution experimental visualization of the break-up of a liquid jet by a gaseo... more High-speed, high-resolution experimental visualization of the break-up of a liquid jet by a gaseous cross-flow has recently become possible due to advances in video camera technology. These visualizations can now be contrasted to high fidelity CFD simulations which are also just becoming possible due to continuing growth of computational capabilities. Such a contrast is expected to go beyond traditional comparisons of time-averaged quantities and focuses on dynamics. For example, comparisons of the characteristic break-up frequency and of the spatial instantaneous features of the jet may serve as validation of the computational model and to yield insight into the physics of the dynamic interplay between the disturbances induced by the injection device and Kelvin-Helmholtz / Rayleigh-Taylor instabilities at the interface. A state-of-the-art second-order coupled Level Set and Volume Of Fluid method (CLSVOF) that can capture liquid-gas interface dynamics is used for the study. High-speed videos of non-turbulent liquid injection in laminar crossflow are used to validate the time- and grid-converged capability of the code to capture upwind wave structures caused by the centrifugal acceleration of the deflected liquid. The extension to increasing air crossflow is also discussed with focus on the column break-up mechanism.

This work presents the results of a study of a liquid jet atomized by a gas cross-flow in the vic... more This work presents the results of a study of a liquid jet atomized by a gas cross-flow in the vicinity of a plane wall normal to the liquid jet axis. Droplets and ligaments with sufficient momentum will impinge on the wall, forming a thin liquid film. A highly time-resolved fluorescent liquid film thickness measurement technique is used together with high speed video to correlate the temporal behavior of jet and droplet impingement with the film thickness. Results of time correlated PDPA and film thickness measurements are also presented, showing the relationship between droplet production and film thickness versus droplet production from the jet alone.

Physics of Fluids, 2009

New insight into the mechanism of liquid jet in crossflow atomization is provided by an analysis ... more New insight into the mechanism of liquid jet in crossflow atomization is provided by an analysis technique based on proper orthogonal decomposition and spectral analysis. Data are provided in the form of high-speed videos of the jet near field from experiments over a broad range of injection conditions. For each condition, proper orthogonal modes (POMs) are generated and ordered by intensity variation relative to the time average. The feasibility of jet dynamics reduction by truncation of the POM series to the first few modes is then examined as a function of crossflow velocity for laminar and turbulent liquid injection. At conditions where the jet breaks up into large chunks of liquid, the superposition of specific orthogonal modes is observed to track long waves traveling along the liquid column. The temporal coefficients of these modes can be described as a bandpass spectrum that shifts toward higher frequencies as the crossflow velocity is increased. The dynamic correlation of these modes is quantified by their cross-power spectrum density. Based on the frequency and wavelength extracted from the videos, the observed traveling waves are linked to the linearly fastest growing wave of Kelvin-Helmholtz instability. The gas boundary layer thickness at the gas-liquid shear layer emerges at the end of this study as the dominant length scale of jet dynamics at moderate Weber numbers.

Immiscible drop collision, as occurring in fuel-oxidizer sprays or in the release of certain fire... more Immiscible drop collision, as occurring in fuel-oxidizer sprays or in the release of certain fire-extinguishing agents, tends to exhibit a much richer behavior with respect to miscible drops collision thanks to the formation of a liquid-liquid interface during impact. For instance, in near-head-on diesel-water drop collisions, ``overlaying'' may occur in which the diesel oil flows from the collision point around the water drop to gather at the opposite location of the drop. To simulate this class of multi-material flows, the combined volume-of-fluid / level set methodology that sharply captures a single liquid-gas interface (Sussman et al, J. of Comp. Phys., 2007) needs to be duplicated for a second, independent interface. In this presentation, we will show that simulation results are not affected by the reconstruction order of the interfaces, as in other surface capturing methods. We will also propose different numerical solutions to treat surface tension in the triple point computational cells, and examine the characteristics of the flow developing at the contact line between the two liquids and air in overlaying head-on collisions.

Evolution of flow of immiscible fluids under high-shear poses severe challenges to the developmen... more Evolution of flow of immiscible fluids under high-shear poses severe challenges to the development of accurate and robust numerical techniques that can maintain a sharp separating interface. The implicit volume of fluid (VOF) advection using High Resolution Interface Capturing (HRIC) scheme offers the advantage of numerical stability at large time steps, but has been observed to cause interface diffusion at high shear. Advection using the standard Piecewise Linear Interface Calculation (PLIC), on the other hand, requires much smaller time steps. We have developed an efficient, accurate coupling approach between a sharp-interface front-tracking library and an unstructured-grid implicit flow solver. The high efficiency results from a localized searching algorithm for grid cells close to the interface. The accuracy is obtained from a conservative interfacial force transfer between front and grid that preserves momentum balance and from a novel approach for constructing the density profile across the interface. Validation of the method with tests of drop deformation in high shear will be presented, with attention to efficiency and accuracy. The performance of this stand-alone front-tracking capability on unstructured grids suggests that the coupled approach may be well suited for simulations in complex domains.

We propose two simple models for evaluating the role of diffusion in the shear layer behind the t... more We propose two simple models for evaluating the role of diffusion in the shear layer behind the triple point in the decaying portion of a detonation cell. Both models are based on an idealized detonation cell cycle, with imposed detonation speed profile. Following the standard triple-point analysis at the shock front, time-accurate integration of the species evolution is carried out using a detailed reaction mechanism and simplified models of mixing. The first model examined considers fast mixing of the fluid across the shear layer behind the triple point to map ignition enhancement as a function of mixture fraction. The second model is to treat the mixing layer as a one-dimensional, temporally-developing diffusion layer. Both model and simulations show that the effect of diffusion at the shear layer in the decaying portion of a detonation cell depends, as expected, on the activation energy of the reacting mixture. Negligible for regular detonation parameters, diffusion is found to significantly shorten the colder layer ignition delay in high-activation energy mixtures. Laminar flames are observed to emerge from the temporally developing shear layer in some cases.

The role played by the air stream in selecting the dominant wave mode in liquid jet in crossflow ... more The role played by the air stream in selecting the dominant wave mode in liquid jet in crossflow break-up is investigated in an experimental facility where a rectangular air jet is directed orthogonally toward the liquid column. The column is seen to immediately broaden upon impact of the air jet, with surface waves initiating along the windward surface. The ensuing break-up dynamics is captured by two synchronized high-speed cameras with identical lenses and orthogonal fields of view. The side view of the windward surface shows a wavelike structure whose peaks correspond, in the top view of the column, to transverse ligaments that increase in length with distance. The wave troughs correspond to thin sheets which distend, stretch, and eventually perforate into smaller droplets leaving behind the thicker transverse ligaments. The coherent structures of this complex dynamics are revealed by the simultaneous analysis of the two synchronized image sequences in a range of turbulent and non-turbulent flow conditions. Three-dimensional reconstruction aspects will be discussed, particularly how to identify the dominant wavelike modes that appear periodically in the video sequences.

Journal of Fluid Mechanics, 2005

An investigation of detonation diffraction through an abrupt area change has been carried out via... more An investigation of detonation diffraction through an abrupt area change has been carried out via a set of two-dimensional numerical simulations parameterized by the activation energy of the reactant. Our analysis is specialized to a reactive mixture with a perfect gas equation of state and a single-step reaction in the Arrhenius form. Lagrangian particles are injected into the flow as a diagnostic tool for identifying the dominant terms in the equation that describes the temperature rate of change of a fluid element, expressed in the shock-based reference system. When simplified, this equation provides insight into the competition between the energy release rate and the expansion rate behind the diffracting front. The mechanism of spontaneous generation of transverse waves along the diffracting front is carefully analysed and related to the sensitivity of the reaction rate to temperature. We study in detail three highly resolved cases of detonation diffraction that illustrate different types of behaviour, super-, sub-and near-critical diffraction.

Atomizing liquids by injecting them into crossflows is a common approach to generate fuel sprays ... more Atomizing liquids by injecting them into crossflows is a common approach to generate fuel sprays in gas turbines and augmentors. The mechanisms by which the liquid jet initially breaks up, however, are not well understood. To analyze the instability mechanism of the liquid column, we perform proper orthogonal decomposition of side view images extracted from detailed simulations of the near injector primary atomization region. This analysis shows a single dominant wavelength with the associated interface corrugation traveling downstream with the jet. Using consistent temporal averaging of the simulation data we extract mean interface geometries and boundary layer velocity profiles. These are used to calculate the most unstable wavelength of the shear layer instability following the procedure of Boeck & Zaleski (2005). The theoretical wavelengths are comparable to those extracted from the simulation data. In addition to shear layer instability we analyze Rayleigh-Taylor as a potential instability mechanism of the liquid column.

Turbulent premixed combustion is present in many power generation and propulsion systems due to i... more Turbulent premixed combustion is present in many power generation and propulsion systems due to its large energy conversion rate (as compared to non-premixed combustion) and its potential for reduced emissions (at the lean limit). As a result, the study of turbulent premixed flames has received substantial attention in the past through experiment, analysis and simulation. In the recent past, unsteady Computational Fluid Dynamics (CFD) based models have been increasingly leveraged towards the in depth study of the physics of turbulent premixed flames. The bulk of this effort focuses on the response of the flame to turbulence. In contrast, we focus on the opposite problem, i.e. the modification of the turbulent flowfield by the flame. This topic has also received some attention but with a strong emphasis on planar (in the mean), flames propagating normal to the flow. Instead, we focus on flameholder-stabilized ducted flames, i.e. ones in which the flame is confined and substantially inclined to the incoming flow. The fundamental mechanisms by which the flame impacts the flow, i.e. dilatation, baroclinic vorticity generation and molecular diffusion enhancement are discussed in detail and their relative impact quantified. Limitations of modeling these mechanisms in current state of the art CFD models are also addressed.

Chemical Physics, 2011

The combination of short-range repulsive and long-range attractive forces in many-body dissipativ... more The combination of short-range repulsive and long-range attractive forces in many-body dissipative particle dynamics (MDPD) is examined at a vapor/liquid and liquid/solid interface. Based on the radial distribution of the virial pressure in a drop at equilibrium, a systematic study is carried out to characterize the sensitivity of the surface tension coefficient with respect to the inter-particle interaction parameters. For the first time, the approximately cubic dependence of the surface tension coefficient on the bulk density of the fluid is evidenced. In capillary flow, MDPD solutions are shown to satisfy the condition on the wavelength of an axial disturbance leading to the pinch-off of a cylindrical liquid thread; correctly, no pinch-off occurs below the cutoff wavelength. Moreover, in an example that illustrates the cascade of fluid dynamics behaviors from potential to inertial-viscous to stochastic flow, the dynamics of the jet radius is consistent with the power law predictions of asymptotic analysis. To model interaction with a solid wall, MDPD is augmented by a set of bell-shaped weight functions; hydrophilic and hydrophobic behaviors, including the occurrence of slip in the latter, are reproduced using a modification in the weight function that avoids particle clustering. The dynamics of droplets entering an inverted Y-shaped fracture junction is shown to be correctly captured in simulations parametrized by the Bond number, confirming the flexibility of MDPD in modeling interface-dominated flows.

Atomization of a liquid fuel jet by a high speed cross-flowing gas plays a critical role in many ... more Atomization of a liquid fuel jet by a high speed cross-flowing gas plays a critical role in many propulsion devices. High fidelity simulation offers the potential of a better understanding and enhancement of this atomization process. In this work, a computationally efficient hybrid Eulerian-Lagrangian approach is coupled with a droplet evaporation model and is used to probe the impact of evaporation on the spray development. The Coupled Level Set and Volume of Fluid (CLSVOF) method is used to directly calculate the breakup and coalescence of the liquid-gas interface. Adaptive Mesh Refinement (AMR) is adopted to achieve high resolution at the interface. Small fuel droplets in dilute regions are removed from the Eulerian description, transformed into Lagrangian particles and tracked by a discrete phase transport model. The coupling of the spray evaporation to the gas phase is examined with respect to jet blockage, spray penetration, and overall far-field spray dispersion. The calculation is validated with flow rate, spray size distribution and velocity data acquired in a spray rig at high-Weber, high-Reynolds number injection conditions. The effect of evaporation on spray distribution is also discussed.

Capillary pinch-off results carried out with the Many-Body Dissipative Particle Dynamics (MDPD) m... more Capillary pinch-off results carried out with the Many-Body Dissipative Particle Dynamics (MDPD) method are compared with the two-phase continuum discretization of hydrodynamics. The MDPD method provides a mesoscale description of the liquid-gas interface -- molecules can be thought of as grouped in particles with modeled Brownian and dissipative effects. No liquid-gas interface is explicitly defined; surface properties, such as surface tension, result from the MDPD interaction parameters. In side-to-side comparisons, the behavior of the MDPD liquid is demonstrated to replicate the macroscale behavior (thin interface assumption) calculated by the Combined Level Set-Volume of Fluid (CLSVOF) method. For instance, in both the continuum and mesoscale discretizations the most unstable wavelength perturbation leads to pinch-off, whereas a smaller wavelength-to-diameter ratio, as expected, does not. The behavior of the virial pressure in MDPD will be discussed in relation to the hydrodynamic capillary pressure that results from the thin interface assumption.

High-speed, high-resolution experimental visualization of the break-up of a liquid jet by a gaseo... more High-speed, high-resolution experimental visualization of the break-up of a liquid jet by a gaseous cross-flow has recently become possible due to advances in video camera technology. These visualizations can now be contrasted to high fidelity CFD simulations which are also just becoming possible due to continuing growth of computational capabilities. Such a contrast is expected to go beyond traditional comparisons of time-averaged quantities and focuses on dynamics. For example, comparisons of the characteristic break-up frequency and of the spatial instantaneous features of the jet may serve as validation of the computational model and to yield insight into the physics of the dynamic interplay between the disturbances induced by the injection device and Kelvin-Helmholtz / Rayleigh-Taylor instabilities at the interface. A state-of-the-art second-order coupled Level Set and Volume Of Fluid method (CLSVOF) that can capture liquid-gas interface dynamics is used for the study. High-speed videos of non-turbulent liquid injection in laminar crossflow are used to validate the time- and grid-converged capability of the code to capture upwind wave structures caused by the centrifugal acceleration of the deflected liquid. The extension to increasing air crossflow is also discussed with focus on the column break-up mechanism.

This work presents the results of a study of a liquid jet atomized by a gas cross-flow in the vic... more This work presents the results of a study of a liquid jet atomized by a gas cross-flow in the vicinity of a plane wall normal to the liquid jet axis. Droplets and ligaments with sufficient momentum will impinge on the wall, forming a thin liquid film. A highly time-resolved fluorescent liquid film thickness measurement technique is used together with high speed video to correlate the temporal behavior of jet and droplet impingement with the film thickness. Results of time correlated PDPA and film thickness measurements are also presented, showing the relationship between droplet production and film thickness versus droplet production from the jet alone.