bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of excitation on gas centered swirl coaxial injectors
Authors: Yoon Youngbin , Park Gujeong , Oh Sukil , Bae Jinhyun 
Published: September 2017

Studies on combustion instability in liquid rocket engines are important in improving combustion efficiency andpreventing combustion chamber losses. To prevent combustion instability, methods such as baffles and cavities are used. The injector is located in the middle of the perturbation-propagation process in the rocket engine, so it is important to study the suppression of combustion instability using the design of the injector. Much research has been focused on the study of liquid excitation in a single injector; however, the actual injector used in a liquid rocket engine is a coaxial injector. In this study, the dynamic characteristics of a gas-centred swirl coaxial injector were investigated by varying the gap thickness and momentum-flux ratio. Spray photographs were captured by synchronizing a stroboscope and digital camera, and a high-speed camera and Xenon lamp were also used. To measure the liquid film, a measurement system was implemented using the electrical conductance method. For excitation of the gas, an acoustic speaker was used to impart a frequency to the gas. The gGas velocity and effect of excitation were measured by hot-wire anemometry. A mechanical pulsator was used for liquid flow excitation. Liquid fluctuation was measured by a dynamic pressure sensor. In both gas and liquid excitation cases, the gain increased as the gap thickness decreased and the momentum-flux ratio increased. From these results, it can be concluded that gap thickness and momentum-flux ratio are major factors in suppressing combustioninstability. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4653
Numerical simulation of superheated jets using an Eulerian method.
Authors: Lyras Konstantinos , Dembele Siaka , Madhav Rao Vendra C. , Wen Jennifer 
Published: September 2017

Flash boiling is the rapid phase change of a pressurised fluid that emerges in ambient conditions below its vapourpressure. Flashing can occur either inside or outside the nozzle depending on the local pressure and geometry and the bubble formation leads to interfacial interactions that eventually influence the emerging spray. Lagrangian methods which exist in literature to simulate the flash atomisation and inter-phase heat transfer employ many sim- plifying assumptions. Typically, sub-models used for the break-up, collisions and evaporation introduce an extensive empiricism that might result in unrealistic predictions for cases like flashing. In this study, a fully Eulerian approach is selected employing the Σ − Y model proposed by Vallet and Borghi. The model tracks liquid structures of any shape and computes the spray characteristics comprising a modified version for the transport equation of the sur- face density. The main goal of this study is to investigate the performance of this model in flash boiling liquids using the Homogeneous Relaxation Model (HRM) developed by Downar-Zapolski, a model capable of capturing the heat transfer under sudden depressurisation conditions accounting for the non-equilibrium vapour generation. The model in this present study considers that the instantaneous quality would relax to the equilibrium value over a given timescale which is calculated using the flow field values. A segregated approach linking the HRM and Σ − Y is implemented in a compressible formulation in an attempt to quantify the effects of flash boiling in the spray dynamics. The developed model is naturally implemented in RANS in a dedicated solver HRMSonicELSAFoam. Results from simulations of two-phase jets of different subcooled fluids through sharp-edged orifices show that the proposed approach can accurately simulate the primary atomisation and give reliable predictions for the droplet sizes and distribution. Strong effects of the flashing and turbulent mixing on the jet are demonstrated. The model istested for turbulent flows within small nozzles and was developed within the open source code OpenFOAM.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4667
Comparison between analytical, numerical, and experimental results of grouping effects in droplet streams
Authors: Roth Norbert , Gomaa Hassan , Livne Alon , Katoshevski David , Weigand Bernhard 
Published: September 2017

Grouping of droplets was studied in monodisperse droplet streams. This very controllable system allows to studybasic effects. In experiments droplet streams with monodisperse droplets were generated, however, with initially two different inter droplet spacing. A larger inter droplet spacing is followed by a little bit smaller one, which is followed by a larger one and so on. Due to this initial boundary condition groups of two droplets form, which approach each other and finally coagulate. It was found, that the velocity of the droplet approach is linearly dependent on the spacing between the droplets. This process was simulated by direct numerical simulation using the in-house code FS3D. The results of the simulations show the ame linear behaviour. For larger computational domains thenumerical results approach the experimental results.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4685
Design and experiments to investigate spray and impingement characteristics of a common rail type lubrication system
Authors: Stark Matthias , De Risi Arturo , Giangreco Marcelo , Diggelmann Simon 
Published: September 2017

This paper reports on the establishment of a testing facility to investigate spray and impingement characteristics ofa recently developed, fully adaptive lubrication system for large two stroke marine diesel engines. The reported part of this research relates to development steps towards the new lubrication system as well as the implementation of a dedicated testing facility and the establishment of validation approaches in order to corroborate technology developments in this context.The major objective of this development yields an optimization of lubricant utilization and at the same time a significant reduction of lubricant fraction in the exhaust gas. A requisite to obtain the desired level of flexibility calls for a revised approach in injecting the lubricant. The desired flexibility of the new lubrication approach foresees a cycle based adjustment of the injected amount of lubricant as well as the injection pressure in order to provide the possibility to shape the injection spray pattern. Concept studies nominate the application of a common rail system with integrated needle lift type injectors and adjustable injection pressure as compliant with the requisite to inject the lubricant with a high level of flexibility.This paper hence encompasses design and development aspects of the new lubrication system but most of all highlights steps in developing a validation concept in order to compare common lubrication systems with the new type of lubrication system.Initial results of the test cell provide an insight regarding relevant information on the injection spray characteristics over the full engine load range as well as the possibility to compare common lubrication system performance with the new common rail lubrication system.A comparison between measurement and simulation results provide the possibility to implement experimentallygained data in a neuronal network in order to enhance the predictive quality of the simulation tool.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4688
Spray Conditioning for the Preparation of Spray Dried Submicron Particles
Authors: Gorny Ramona Klaudia , Schaldach Gerhard , Walzel Peter , Thommes Markus 
Published: September 2017

Particle size reduction down to the submicron range (0.1-1 µm) is an effective option to increase the bioavailabilityof low water soluble active pharmaceutical ingredients. According to the Nernst-Brunner equation, the preparation of submicron sized particles increases the specific surface area, thus increases the dissolution rate. Conventional spray drying devices for submicron particles show certain limitations. The main challenge is the preparation of small and uniform droplets during the atomisation step. In this work, fine droplets were generated combining a nozzle with a droplet separator. Therefore, the aerosol is generated with a pneumatic nozzle and is sprayed into a cyclone droplet separator. Depending on the characteristics of the cyclone, droplets larger than the cut-off-size were separated and returned into the liquid feed. The conditioned aerosol at the top of the cyclone separator can then be introduced into the drying chamber. With this concept the usable part is separated, thus no classification process after drying is necessary. The investigations show that the dependencies during atomisation of the droplets size on the liquid-to-gas mass flow ratio µm and the liquid properties (e.g. viscosity) do not apply to the separation step. The conditioned aerosol only depends on the separation characteristics of the cyclone droplet separator. However, the amount of droplets separated is determined by the atomisation step. Hence, the amount of droplets smaller than the cut-off-size can be increased by decreasing the droplet size of the primary aerosol. This is realised by secondary droplet fragmentation. An impact surface causes breakup of the droplets of theprimary aerosol before separation. The investigations show an increased amount of droplets &lt;2µm.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4701
Splashing of a very viscous liquid drop impacting onto a solid wall wetted by another liquid
Authors: Kittel Hannah M , Roisman Ilia V , Tropea Cameron 
Published: September 2017

In this experimental work the main focus is on the impact of a single drop of a very viscous liquid onto a thin,horizontal wall film of different liquid. Splashing resulting from drop impact onto a wetted wall occurs in many natural and engineering applications like in internal combustion engines and spray cooling. While the splashing threshold for low viscosity liquid drops has been extensively examined, impact of a very viscous drop is much less studied. The viscosities of drop and wall film liquids are varied up to kinematic viscosities of 100,000 mm²/s. The liquids used in the experiments are miscible.The impact outcome is determined by the impact parameters and fluid properties. The effect of very viscous liquids used as drop fluid and as wall film liquid on the kinematic of the corona expansion is investigated in the experiments. The results of drop impact onto solid walls are compared to obtain the limiting asymptotic values for the splashing threshold. Finally, a semi-empirical model for the splashing threshold, for the maximum spreading radius Dmax and for the maximum spreading times tmax viscous liquids.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4702
Experimental investigation of Ethane and Propane injection under sub- and super-critical conditions
Authors: Vallee Nathalie , Ribert Guillaume , Blaisot Jean-Bernard , Lisiecki Denis 
Published: September 2017

Studying a fluid flow under high-pressure conditions through reliable experiments is still nowadays a challenge.When the chamber pressure exceeds the critical pressure of working fluids the supercritical state of matter is reached and the distinction between gas and liquid becomes blurred. For such special conditions, experimental data are scarce and need to be consolidated. Indeed, the modification of the local refractive index induced by den- sity gradient needs to be analyzed with appropriate image-based technique.In the present study, the REFINE test bench (Real-gas Effect on Fluid Injection: a Numerical and Experimental study) has been designed at CORIA Lab to study the non-reactive injection of Ethane and Propane into Nitrogen under sub- and supercritical conditions. The ambient gas pressure can be raised up to 6 MPa and warmed up to 573 K to scan sub- and trans-critical injections. The chamber is equipped with two perpendicular optical axes allowing simultaneously different optical diagnostics. Experimental data are collected from shadowgraph and dif- fused backlight illumination techniques. Quantitative measurements of jet spre ding angle and breakup length arecompared to results coming from literature exhibiting multiple flows topologies.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4708
Detailed simulation of air-assisted spray atomization: effect of numerical scheme at intermediate Weber number
Authors: Tretola Giovanni , Vogiatzaki Konstantina , Navarro-Martinez Salvador 
Published: September 2017

Numerical simulations are often used to understand spray atomisation and estimate the size of the liquid fragments.Several techniques (Level Set, Volume of Fluid, Smooth Particle Hydrodynamics, among others) exist to compute multiphase flows and potentially represent liquid-break-up. However, the complexity of the breakup process and the wide range of scales prevents the use of an unified approach to simulate the complete spray. Numerical techniques face different challenges depending on the spray characteristics. The incorrect representation of surface forces in capillary dominated flows, creates large parasitic currents that distort and in some cases destroy the interface. Methods that perform well in the capillary regime aim to capture the interface directly and the surface radius cur- vature is therefore larger than the mesh size. However, this creates large constrains on the mesh resolution and limits its applications to low Weber number flows, when there is no extensive atomization. Methods that simulate large Weber number flows (typical of industrial injectors) do not resolve the interface directly and the mesh is larger than the smallest radius of curvature. These models often have numerical or artificial diffusion that destroys small scale structures and alters the break-up. However, even at large Weber flows, the spray formation can be affected by errors due to the local imbalance between pressure and surface tension forces and interface curvature errors. Numerical schemes work around these problems by adjusting the amount of numerical diffusion of the scheme depending on the spray application. Intermediate Weber number sprays are well suited to study the performance of numerical methods as they exhibit hybrid behaviour between capillary flows and full atomization. In the present work an intermediate gas Weber of a laboratory air-blast atomiser is investigated using a volume of fluid approach. The amount of numerical diffusion is controlled by a compressive factor in the volume of fluid transport equation. The effect of the compressive term on spray atomization and droplet size distribution is explored. The results suggestthat the optimal amount of diffusion depends on the local Weber number.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4712
Expansion rates of bubble clusters in superheated liquids
Authors: Dietzel Dirk , Hitz Timon , Munz Claus-Dieter , Kronenburg Andreas 
Published: September 2017

The present work analyses the growth of multiple bubbles in superheated liquid jets by means of direct numericalsimulations (DNS). A discontinuous Galerkin approach is used to solve the Euler equations and an adequate in- terface resolution is ensured by applying finite-volume sub-cells in cells with interfaces. An approximate Riemann solver has been adapted to account for evaporation and provides consistency of all conserved quantities across the interface. The setup mimics conditions typical for orbital manoeuvring systems when liquid oxygen (LOX) is injected into the combustion chamber prior to ignition. The liquid oxygen will then be in a superheated state, bubble nucleation will occur and the growth of the bubbles will determine the break-up of the liquid jet. The expansion rates of bubble groups under such conditions are not known and standard models rely on single bubble assumptions. This is a first DNS study on bubble-bubble interactions in flash boiling sprays and on the effects of these interactions on the growth rates of the individual bubbles. The present simulations resolve a small section of the jet close to the nozzle exit and the growth of bubble groups inside of the jet is analysed. The results suggest that an individual bubble within the group grows more slowly than conventional models for single bubble growth would predict. The reduction in bubble growth can amount to up to 30% and depends on the distances between the bubbles and the number of bubbles within the bubble group. In the present case, the volume expansion of the superheated liquiddecreases by approximately 50% if the distance between the bubbles is doubled.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4714
Polydisperse spray flames in vortex flows
Authors: Dagan Yuval , Katoshevski David , Greenberg Barry J 
Published: September 2017

A new mathematical analysis of the dynamics of laminar spray diffusion flames in the vicinity of a vortex flow fieldis presented. The governing equations for a spray evaporating in an unsteady vortex are studied. New similarity solutions are found for the dynamics of the spray and the flame it supports. Analytical solutions for the spray flames are derived using Schvab-Zeldovich parameters, through which the radial evolution of the flames is found. The results based on the solution reveal the significant influence the droplets size has on the diffusion flame dynamicsin the vicinity of vortical flows.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4716
Comparison between numerical and experimental water-in-oil dispersion in a microchannel
Authors: Tarlet Dominique , Desjonquères Philippe , Ménard Thibault , Bellettre Jérôme 
Published: September 2017

The dispersion of water inside a flow of oil is investigated in a microfluidic device, producing a water-in-oilemulsion. The liquid–liquid flow mainly differs from those presented in existing literature through its high capillary number (between 3 and 14), and in the head-on collision between water and oil streams. By comparing with experimental data, numerical simulations can provide more information about the topology of the flow. A coupled Volume of Fluid and Level Set method (CLSVOF) is used to treat the interface between both phases and incompressible Navier-Stokes equations are solved. Three set of parameters, close to those in the experimental setup, are investigated to compare experimental and numerical results. The comparison between experiments and simulation provides a precise knowledge of the liquid-liquid dispersion process and the overall flow patternwithin the microfluidic device.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4717
Modelling of spheroidal drop evaporation with non-uniform temperature conditions
Authors: Tonini Simona , Cossali Gianpietro Elvio , Ravasio Stefano 
Published: September 2017

The heating and evaporation of single component spherical and spheroidal drops in gaseous quiescentenvironment are predicted, accounting for the effect of a non-uniform distribution of the temperature at the drop surface. The analytical solution of the species conservation equations in the proper coordinate system (spherical/spheroidal) is implemented to numerically solve the energy equation in a rectangular domain. The effect of temperature disuniformity on the local Nusset number and global heat and evaporation rates iscalculated for different species, drop deformation and gaseous temperature.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4721
Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water.
Authors: Jasper Sarah , Hussong Jeanette , Lindken Ralph 
Published: September 2017

High pressure water jets (HPWJ) are frequently used in industrial applications like cleaning, further processing of workpieces or cutting of materials. In a joint research program with the International Geothermal Centre (GZB) the HPWJ process is adapted to the field of rock drilling to develop and enhance an innovative drilling technology for geothermal applications. In this case, the HPWJ is used to cut and destroy rock in deep geothermal reservoirs to make them accessible for energy generation. This transfer requires a broad knowledge of the process and interaction between the HPWJ and the rock surface. The challenges in analysis and characterization of the process are high velocities of the water jet of several hundred meters per second based on the high pump pressure of up to 180 MPa and the very small spatial expansion of the field of interest between the nozzle outlet and the rock surface, which is within a few centimeters. The objective of the present work is the visualization of a HPWJ in diverse fluids as a first step to increase the process knowledge of waterjet cutting of rocks. Tests are performed in air, water and slurry respectively and a parametric study is carried out to examine the influence of different operating parameters on the HPWJ formation and structure. Moreover, the influence of the surrounding fluid on the HPWJ is investigated.Optical measurement techniques are applied to analyze the HPWJ and results will be presented. The high velocities, the very small spatial expansion and the dense liquid jet represent challenges to the application of these measurement techniques. High speed photography in terms of shadow experiments is used for visualization and relevant spray parameters are evaluated with common spray analysis techniques. Adopting the double frame technique, well-known with particle image velocimetry (PIV), an estimation of the fluid velocity on the boundary of the HPWJ is performed. In addition to the shadowgraph analysis, PIV in auto-correlation mode with fluorescent tracers is applied to analyze velocity fields, the dimension of the potential core as well as the interaction with the surrounding fluid.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4736