bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi-scale Eulerian-Lagrangian simulation of a liquid jet in cross-flow under acoustic perturbations
Authors: Thuillet Swann , Zuzio Davide , Rouzaud Olivier , Gajan Pierre 
Published: September 2017

The design of modern aeronautical propulsion systems is constantly optimized to reduce pollutant emissions whileincreasing fuel combustion efficiency. In order to get a proper mixing of fuel and air, Liquid Jets Injected in gaseous Crossflows (LJICF) are found in numerous injection devices. However, should combustion instabilities appear in the combustion chamber, the response of the liquid jet and its primary atomization is still largely unknown. Coupling between an unstable combustion and the fuel injection process has not been well understood and can result from multiple basic interactions.The aim of this work is to predict by numerical simulation the effect of an acoustic perturbation of the shearing air flow on the primary breakup of a liquid jet. Being the DNS approach too expensive for the simulation of complex injector geometries, this paper proposes a numerical simulation of a LJICF based on a multiscale approach which can be easily integrated in industrial LES of combustion chambers. This approach results in coupling of two models: a two-fluid model, based on the Navier-Stokes equations for compressible fluids, able to capture the largest scales of the jet atomization and the breakup process of the liquid column; and a dispersed phase approach, used for describing the cloud of droplets created by the atomization of the liquid jet. The coupling of these two approaches is provided by an atomization and re-impact models, which ensure liquid transfer between the two-fluid model and the spray model. The resulting numerical method is meant to capture the main jet body characteristics, the generation of the liquid spray and the formation of a liquid film whenever the spray impacts a solid wall.Three main features of the LJICF can be used to describe, in a steady state flow as well as under the effect of the acoustic perturbation, the jet atomization behavior: the jet trajectory, the jet breakup length and droplets size and distribution.The steady state simulations provide good agreement with ONERA experiments conducted under the same condi- tions, characterized by a high Weber number (We&gt;150). The multiscale computation gives the good trajectory of the liquid column and a good estimation of the column breakup location, for different liquid to air momentum flux ratios. The analysis of the droplet distribution in space is currently undergoing. A preliminary unsteady simulation was able to capture the oscillation of the jet trajectory, and the unsteady droplets generation responding to the acousticperturbation.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4697
Planar droplet sizing: Application to a spray of Jet A1 kerosene
Authors: Doublet Pierre , Lempereur Christine , Bodoc Virginel , Orain Mikael , Gajan Pierre 
Published: September 2017

Optical techniques are widely employed for their non-intrusive behavior and are applied to two-phase flowinvestigations. Until now, the most commonly used technique to determine the droplet size is the Phase Doppler Anemogranulometry, although it is time consuming for an overall injector characterization. An imaging technique called Planar Droplet Sizing has been used to offer an alternative and provide a spatially-resolved 2D map of the Sauter Mean Diameter (SMD). The measurement is based on the ratio between laser-induced fluorescence and scattered light intensities which are assumed to be proportional respectively to the droplet volume and droplet surface area. However, previous studies revealed that the dependence of fluorescence intensity on the droplet volume can be altered by the absorption of light in the liquid. The scattered light intensity depends on the scattering angle and intensity variations within the field of view must be avoided.The aim of this study is to make the PDS technique operational for a Jet A-1 kerosene spray. A strong absorption of liquid kerosene appears under UV excitation at 266 nm making the technique unsuitable. Under visible excitation at 532 nm, a fluorescent tracer (Pyrromethene 597) must be added to the kerosene to enhance the fluorescence signal. To prevent scattered light intensity variations within the field of view, an optimal scattering angle close to 115° is required. An image processing algorithm is proposed in order to reduce the effects ofmultiple scattering.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4698
Behaviour of free falling viscoelastic liquid jets
Authors: Tirel Christophe , Renoult Marie-Charlotte , Dumouchel Christophe , Blaisot Jean-Bernard 
Published: September 2017

In a recent work, a protocol to measure the relaxation time of dilute polymer solutions, known to be challenging,has been established [1]. This protocol is based on a 2D multi-scale description of free-falling low velocity viscoelastic liquid jets. Although the relaxation time reached an asymptotic value for high jet velocities, a significant dependence with the jet velocity is observed for low velocities. The present work reconsiders these previous experimental data using a 3D multi-scale analysis in order to identify the origin of the dependence between the relaxation time and the jet velocity. The 3D analysis demonstrates the importance of a velocity–dependent coalescence mechanism in the jet behaviour. Thanks to a simple model of jet deformation it is demonstrated that this coalescence mechanism prevents the elasto-capillary contraction of the smallest scales from occurring whenthe jet velocity is reduced.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4700
X-ray diagnostics of dodecane jet in spray A conditions using the new one shot engine (NOSE)
Authors: Hugo Ajrouche , Ibrahim Chiboub , Ob Nilaphai , Sébastien Dozias , Bruno Moreau , Camille Hespel , Fabrice Foucher , Christine Mounaïm-Rousselle , Jean-Michel Pouvelse , Eric Robert 
Published: September 2017

Quantifying liquid mass distribution data in the dense near nozzle area to develop and optimize diesel spray byoptical diagnostic is challenging. Optical methods, while providing valuable information, have intrinsic limitations due to the strong scattering of visible light at gas-liquid boundaries. Because of the high density of the droplets near the nozzle, most optical methods are ineffective in this area and prevent the acquisition of reliable quantitative data. X-ray diagnostics offer a solution to this issue, since the main interaction between the fuel and the X-rays is absorption, rather than scattering, thus X-ray technique offers an appealing alternative to optical techniques for studying fuel sprays. Over the last decade, x-ray radiography experiments have demonstrated the ability to perform quantitative measurements in complex sprays. In the present work, an X-ray technique based on X-ray absorption has been conducted to perform measurements in dodecane fuel spray injected from a single-hole nozzle at high injection pressure and high temperature. The working fluid has been doped with DPX 9 containing a Cerium additive, which acts as a contrast agent. The first step of this work was to address the effect of this dopant, which increases the sensitivity of X-ray diagnostics due its strong photon absorption, on the behavior and the physical characteristics of n-dodecane spray. Comparisons of the diffused back illumination images acquired from n- dodecane spray with and without DPX 9 under similar operating conditions show several significant differences. The current data show clearly that the liquid penetration length is different when DPX 9 is mixed with dodecane. To address this problem, the dodecane was doped with a several quantities of DPX containing 25% ± 0.5 of Cerium. Experiments show that 1.25% of Ce doesn’t affect the behaviour of spray. Radiography and density measurements at ambient pressure and 60 bars are presented. Spray cone angle around 5° is obtained. The obtained data shows that the result is a compromise between the concentration of dopant for which the physical characteristics of thespray do not change and the visualization of the jet by X-ray for this concentration.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4705
Weakly nonlinear instability of a viscous liquid jet
Authors: Brenn Günter , Renoult Marie-Charlotte , Mutabazi Innocent 
Published: September 2017

Aweakly nonlinear stability analysis of an axisymmetric viscous liquid jet is performed. The calculation is based ona small-amplitude perturbation method and restricted to second order. Contrary to the inviscid jet and the planar viscous sheet cases studied by Yuen in 1968 [1] and Yang et al. in 2013 [2], respectively, a part of the solution results from a polynomial approximation of Bessel functions. Results on interface shapes for a small wave number and initial perturbation amplitude, four different Ohnesorge numbers, taking into account the approximate part or not, are used to predict the influence of liquid viscosity on satellite drop formation and evaluate the influence of the approximation. It is observed that the liquid viscosity has a retarding effect on satellite drop formation, in agreement with previous experimental and numerical work. In addition, it is found that the approximate terms can be reasonably ignored, providing a simpler viscous weakly nonlinear model for the description of the first nonlinearity growth in liquid jets.The present work replaces the ILASS 2016 paper [3] by the authors on the same subject.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4711
Modelling and validation of near-field Diesel spray CFD simulations based on the Σ -Y model
Authors: Pastor J.M. , Desantes J.M. , García-Oliver J.M. , Pandal A. , Naud B. , Matusik K. , Duke D. , Kastengren A. , Powell C. , Schmidt D.P. 
Published: September 2017

Diesel spray modelling still remains a challenge, especially in the dense near-nozzle region. This region is difficultto experimentally access and also to model due to the complex and rapid liquid and gas interaction. Modelling approaches based on Lagrangian particle tracking have struggled in this area, while Eulerian modelling has proven particularly useful. An interesting approach is the single-fluid diffuse interface model known as Σ-Y, based on scale separation assumptions at high Reynolds and Weber numbers. Liquid dispersion is modelled as turbulent mixing of a variable density flow. The concept of surface area density is used for representing liquid structures, regardless of the complexity of the interface.In this work, an implementation of the Σ-Y model in the OpenFOAM CFD library is applied to simulate the ECN Spray A in the near nozzle region, using both RANS and LES turbulence modelling. Assessment is performed with measurements conducted at the Advanced Photon Source at Argonne National Laboratory (ANL). The ultra-small- angle x-ray scattering (USAXS) technique has been used to measure the interfacial surface area, and x-rayradiography to measure the fuel dispersion, allowing a direct evaluation of the Σ-Y model predictions.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4715
Quantification of diesel injector dribble using 3D reconstruction from x-ray and DBI imaging
Authors: Crua Cyril , Sechenyh Vitaliy , Turner Jack , Sykes Dan , Duke Daniel J , Swantek Andrew B , Matusik Katarzyna E , Kastengren Alan , Powell Christopher , Viera Alberto , Payri Raul 
Published: September 2017

Post-injection dribble is known to lead to incomplete atomisation and combustion due to the release of slowmoving, and often surface-bound, liquid fuel after the end of the injection event. This can have a negative effect on engine emissions, performance, and injector durability. To better quantify this phenomenon we present a new image processing approach to quantify the volume and surface area of ligaments produced during the end of injection, for an ECN ‘Spray B’ 3-hole injector. Circular approximation for cross-sections was used to estimate three-dimensional parameters of droplets and ligaments. The image processing consisted in three stages: edge detection, morphological reconstruction, and 3D reconstruction. For the last stage of 3D reconstruction, smooth surfaces were obtained by computation of the alpha shape which represents a bounding volume enveloping a set of 3D points. The object model was verified by calculation of surface area and volume from 2D images of figures with well-known shapes. We show that the object model fits non-spherical droplets and pseudo-cylindrical ligaments reasonably well. We applied our processing approach to datasets generated by different research groups to decouple the effect of gas temperature and pressure on the fuel dribble process. High-speed X-ray phase-contrast images obtained at room temperature conditions (297 K) at the 7-ID beamline of the Advanced Photon Source at Argonne National Laboratory, together with diffused back-illumination (DBI) images captured at a wide range of temperature conditions (293-900 K) by CMT Motores Térmicos, were analysed and comparedquantitatively.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4742
Visualization of pilot flame of an optically-accessible coaxially-staged aero-engine lean-burn fuel injector
Authors: Matsuura Kazuaki , Uesaka Shunya , Iwasaki Tomoyuki , Kurosawa Yoji , Yamada Hideshi , Yamamoto Takeshi , Hayashi Shigeru 
Published: September 2017

The visualization of the pilot flame of a coaxially-staged aero-engine lean-burn fuel injector, not only downstreambut also inside of the pilot nozzle, was successfully performed at realistic aero-engine conditions. Optical access toward the inside of the nozzle was achieved through the inner and outer shrouds, both of which were made of transparent quartz. The image distortion caused by complex contours of the two shrouds was corrected by a method based on optical ray tracing, which realized precise determination of spatial intensity distribution of optical signals. Line-of-sight OH chemiluminescence, cross-sectional OH-LIF, kerosene LIF and kerosene Mie scattering were employed as diagnostic tools. The effects of pilot local air-to-fuel ratio on spray flame structure were revealed, both inside and downstream of the pilot nozzle under stable combustions. As the pilot mixture got rich, the main reaction zone moved from inside of the pilot nozzle to the region near the injector lip downstream of the injector exit. The OH-LIF signal was detected near the central axis surrounded by the fuel spray. It was also observed near the back-step of the pilot nozzle for the rich cases. The experiments under combustion oscillation were also conducted and the correlation of phenomena inside and downstream of the pilot nozzle was captured. It was clarified that the reaction enhancement in the outer part of the lip vortex region was caused by the convectionof rich mixture, which appeared near the pilot atomizer lip at 150~210deg earlier oscillation phase angle.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4752
Simulation of droplet spreading on micro-CT reconstructed 3D real porous media using the volume-of-fluid method
Authors: Aboukhedr Mahmoud , Mitroglou Nicholas , Georgoulas Anastasios , Marengo Marco , Vogiatzaki Konstantina 
Published: September 2017

Droplet impact on porous media has a broad range of applications such as material processing, drug deliveryand ink injection etc. The simulation studies of such processes are rather limited. To represent the spreading and absorption process of the droplet on porous materials, robust numerical schemes capable of accurately representing wettability as well as capillary effects need to be established. The current work, presents one of the first studies of droplet impact on a real porous media geometry model extracted from a micro-CT scan. The process involves processing of CT image and subsequent threshold based on the structures segmentation. The porous geometry is extracted in the form of a STL (STereoLithography) model, which, with the aid of dedicated software like ANSA and SnappyHexMesh, is converted to an unstructured mesh for successful discretization of the flow domain. The solution algorithm is developed within the open source CFD toolbox OpenFOAM. The numerical framework to track the droplet interface during the impact and the absorption phases is based on previous work [1, 2]. The volume-of-fluid (VOF) method is used to capture the location of the interface, combined with additional sharpening and smoothing algorithms to minimise spurious velocities developed at the capillary dominated part of the phenomenon (droplet recession and penetration). A systematic variation of the main factors that affect this process are considered, i.e. wettability, porous size, impact velocity. To investigate the influence of porous structures on droplet spreading, the average porosity of the media is varied between 18.5% and 23.3% . From these numerical experiments, we can conclude that the droplet imbibition mainly depends on the porous wettability and secondly that the recoiling phasecan be observed in the hydrophobic case but not in the hydrophilic case.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4755
Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions
Authors: Traxinger Christoph , Müller Hagen , Pfitzner Michael , Baab Steffen , Lamanna Grazia , Weigand Bernhard , Matheis Jan , Stemmer Christian , Adams Nikolaus A. , Hickel Stefan 
Published: September 2017

Experiments and numerical simulations were carried out in order to contribute to a better understanding and predic-tion of high-pressure injection into a gaseous environment. Specifically, the focus was put on the phase separation processes of an initially supercritical fluid due to the interaction with its surrounding. N-hexane was injected into a chamber filled with pure nitrogen at 5 MPa and 293 K and three different test cases were selected such that they cover regimes in which the thermodynamic non-idealities, in particular the effects that stem from the potential phase separation, are significant. Simultaneous shadowgraphy and elastic light scattering experiments were conducted to capture both the flow structure as well as the phase separation. In addition, large-eddy simulations with a vapor- liquid equilibrium model were performed. Both experimental and numerical results show phase formation for the cases, where the a-priori calculation predicts two-phase flow. Moreover, qualitative characteristics of the formation process agree well between experiments and numerical simulations and the transition behaviour from a dense-gasto a spray-like jet was captured by both.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4756
The liquid penetration of diesel substitutes
Authors: Weiss Lukas , Riess Sebastian , Rezaei Javad , Peter Andreas , Wensing Michael 
Published: September 2017

Diesel fuel consist of several hundreds of substances on organic basis. Experimental and numerical investigationsof this multicomponent fuel are hard to interpret in detail, since the behavior of the multicomponent mixture is complex. Physical and chemical data of this system is not available under engine relevant conditions. Instead, fundamental research substitutes diesel with pure substances, where a big database exists.Prior work already showed, that overall spray propagation (including vapor phase) is nearly independent on the injected fuel. This is due to the high air entrainment at present diesel engine conditions (very high injection pressure and dense ambient atmosphere). The high air entrainment shortly behind the nozzle exit (within the first 5 mm penetration) creates a situation where properties of the ambient gas dominate the spray propagation resulting in similar mass and momentum distributions even for different fuels, if the injection conditions are kept constant. On the other hand, the liquid length is clearly different for different fuels, so that location and time of the phase change differ with consequences on the time available for mixture formation in the gas phase. The paper describes the liquid length as a function of the enthalpy necessary for the phase transition (given by the fuel and fuel temperature at injection) and the injection conditions (ambient gas properties, injector design and injection pressure). We compare two different models describing the enthalpy balance. Siebers et al. presented “Model I”, where mass transfer dominates the enthalpy transfer and evaporation takes place. In our own “Model II” evaporation is suppressed, resulting in a heat transfer driven enthalpy transfer without mass transport. The calculations are validated with experimental data.The liquid length is optically accessible by Mie-Scattering imaging techniques, the complete spray evolution by Schlieren technique. The experimental study was carried out in the high-pressure combustion vessel “OptiVeP” at FAU. The data shown in this paper derived from measurements with dodecane injected at 1200 bar into 613 K ambient. The ambient pressure varies from 1 – 10 MPa. A Continental research injector with a 115 µm hole and L/D of 6.5 was used. Nitrogen atmosphere suppressed ignition.Increasing the ambient pressure leads to a change in the mechanism in phase transition. It switches from a masstransfer dominated regime to a heat transfer dominated regime at high ambient pressures.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4764