Numerical Simulation of the Dispersion and Deposition of a Spray Carried by a Pulsating Airflow in a Patient-Specific Human Nasal Cavity

The present numerical study concerns the dispersion and deposition of a nasal spray in a patient-specific human nose. The realistic three-dimensional geometry of the nasal cavity is reconstructed from computer tomography (CT) scans. Identification of the region of interest, removal of artifacts, segmentation, generation of the .STL file and the triangulated surface grid are performed using the software packages ImageJ, meshLab, and NeuRA2. An unstructured computational volume grid with approximately 15 million tetrahedral grid cells is generated using the software Ansys ICEM-CFD 11.0. An unsteady Eulerian-Lagrangian formulation is used to describe the airflow and the spray dispersion and deposition in the realistic human nasal airway using two-way coupling. A new solver called pimpleParcelFoam is developed, which combines the lagrangianParcel libraries with the pimpleFoam solver within the software package OpenFOAM 3.0.0. A large eddy simulation (LES) with the dynamic sub-grid scale (SGS) model is performed to study the spray in both a steady and a pulsating airflow with an inflow rate of 7.5 L/min (or maximum value in case of the pulsating spray) and a frequency of 45 Hz for pulsation as used in commercial inhalation devices. 10,000 mono-disperse particles with the diameters of 2.4 µm and 10 µm are uniformly injected at the nostrils. In order to fulfil the stability conditions for the numerical solution, a constant time-step of 10−5 s is implemented. The simulations are performed for a real process time of 1 s, since after the first second of the process, all particles have escaped through the pharynx or they are deposited at the surface of the nasal cavity. The numerical computations are performed on the high-performance computer bwForCluster MLS&WISO Production using 256 processors, which take around 32 and 75 hours for steady and pulsating flow simulation, respectively. The study shows that the airflow velocity reaches its maximum values in the nasal valve, in parts of the septum and in the nasopharynx. A complex airflow is observed in the vestibule and in the nasopharynx region, which may directly affect the dispersion and deposition pattern of the spray. The results reveal that the spray tends to deposit in the nasal valve, the septum and in the nasopharynx due to the change in the direction of the airflow in these regions. Moreover, it is found that due to the pulsating airflow, the aerosols are more dispersed and penetrate deeper into the posterior regions and the meatuses where the connections to the sinuses reside.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4628

Analysis of Heat and Flow Characteristics on Spray Cooling Heat Transfer with an Optimized Hexagonal Finned Heat Sink

An experimental study was carried out with a hexagonal finned heat sink to obtain valuable information about the thermal and flow characteristics on spray cooling. Water was used as the refrigerant fluid and was atomized by an air-assisted atomizer and some of the variables that affect spray cooling process, such as breakup length and Sauter Mean Diameter (SMD) were obtained using appropriate correlations. The parameters most influential on the Nusselt number were determined and analyzed. Experiments were conducted for optimized conditions. The jet diameter and spray angle were determined via image processing using macroscopic aspects. Nusselt were demonstrated of hexagonal finned heat sink which optimized according to the Taguchi optimization method. The results of the spray analysis showed that SMD decreases with an increase in either air-liquid mass ratio (ALR) or operating pressure resulting in a more uniform spray. As the liquid flow rate increases in all ALR values, the heat transfer rate also increases markedly. As a results of the experiments, Nusselt number, jet width and spray angle correlations were developed. The relationship of ALR-Nu was demonstrated according to fin height and spraying time.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4772

Visualisation and quantitative analysis of the near nozzle formation and structure of a high pressure water jet in air and water.

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

Fundamental analysis of liquid breakup mechanism in a rotary atomizer with square discharge orifice

An experimental investigation of breakup mechanism in a rotary atomizer with square shape discharge orifice atambient condition has been performed. The effects of a high aspect ratio noncircular discharge channels, particularly a square shape discharge channel, are considered. The motivation of this study is the use of this type of orifice in some small gas turbine engines as well as non-existing observation in literature concerning about high aspect ratio of discharge channel. Visualization experiments are conducted by high speed shadowgraph imaging technique with pulsed light illumination for the first time. The effects of rotational speed and volume flow rate are studied on the breakup structure. The visualizations indicates that the liquid film formed along the channel is pushed to one side of it due to Coriolis force which is dominant in this type of atomizer. Accordingly a crescent shaped liquid film is formed at the square channel exit covering two corners of the square, resulting the combination of Coriolis induced stream mode and surface tension induced stream mode breakup. Observations of the breakup process for different volume flow rates and rotational speeds indicate that the breakup of liquid film stream is dependent on injection conditions and the corresponding cross flow velocity created by atomizer rotation. The breakup regime map is provided as a function of weber number and momentum flux ratio. Four distinct regimes are identified: Rayleigh breakup, bag breakup, multimode breakup, and shear breakup. The present results leads to understandingatomization performance and creating some idea to improved spray quality in this type of atomizer.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5640

Influence of the Fuel Properties on the Injection Process and Spray Development in a large ship diesel Engine

The present paper deals with the influence of fuel properties on the spray behaviour. This influence was studiedexperimentally using a common rail injection system from a medium speed diesel engine. The experiments have been performed with diesel fuel (EN-590) and heavy fuel oil (RMG 180) on a constant volume chamber at room temperature. Comparison of the spray characteristics shows that the heavy fuel oil penetrates deeper in the chamber. However, the diesel spray has a bigger cone angle. These results formed the basis for a further development of the 1D-model [1] to predict the spray penetration by considering the fuel properties and temperature.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4787

Evaluation of the combustion characteristics of isolated droplets of Jet A blended with ethanol and butanol

In light of the potential of ethanol and butanol as alternative fuels for blending with conventional kerosene in gasturbine engines, experimental data regarding the burning characteristics of these blends are required in order tobetter understand their combustion process. In this study, free-falling droplets of Jet A, ethanol, butanol and theirmixtures (20% alcohol in Jet A by volume) were examined in a combustion chamber which providesrepresentative conditions of real flames, both in terms of temperature and oxygen availability. Results show thatthe evolution of droplet diameter for Jet A and its blends with both alcohols are very similar, regardless of theobvious compositional differences. On the other hand, sooting behaviors are found to be quite different, with aclear reduction in the sooting propensity of the Jet A/alcohol mixtures when compared to neat kerosene. Theseresults are consistent with previous studies in gas turbines, suggesting that such blends are viable alternativefuels with similar combustion characteristics to Jet A, but with much less propensity to produce soot. Moreover,this study provides new results on the combustion properties of Jet A/ethanol and Jet A/butanol mixtures, forwhich very scarce data exist in the open literature.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4990

Experimental and Numerical Investigation of Phase Separation due to Multi-Component Mixing at High-Pressure Conditions

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

Spray ignition and local flow properties in a swirled confined spray-jet burner: experimental analysis

Laser ignition was investigated in the swirled, confined CORIA Rouen Spray Burner under ultra-lean conditions (Φ=0.61) with n-heptane as the liquid fuel. Ignition probability was calculated for different spark locations and compared to the non-ignited local flow properties. Mean velocity components of the carrier flow were measured by PDA under spray presence and without spray, and are compared to mean values from PIV. PIV measurements provide information on the instantaneous airflow and the total strain rate. Fuel droplet size-velocity data was measured by PDA. Toluene-PLIF images were acquired to provide information on the local equivalence ratio and the flammability factor. Results show that the outer recirculation zone (ORZ) has a flammability factor close to 1 and the highest ignition probability (~80%). These results have a high correlation with the air velocity field and turbulent kinetic energy. Instantaneous equivalence ratio images and shear rate-velocity fields give important information on local segregation of the flow properties that help to understand the ignition process. The present work provides a useful database for numerical simulations and industry, plus new insight on spray ignition.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4674

Multi-scale Eulerian-Lagrangian simulation of a liquid jet in cross-flow under acoustic perturbations

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>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

Influence of Stokes Number on Collisional Interfacial Area Production Terms within the Σ-Y Eulerian Spray Atomization Model

The present study shows the effects of Stokes number on the modeling of collisional interfacial area productionterms within the Σ-Y model. This model can be employed for CFD simulations of high Weber and Reynolds number sprays using a RANS turbulence modeling. Within the model production of interfacial area is assumed to result from turbulent stretching and turbulent droplet collisions. The modeling of collisional processes requires the calculation of a characteristic turbulent collision velocity. In the present work this velocity was determined under consideration of Stokes number effects leading to turbulent droplet velocity fluctuations attenuated with respect to the gas phase fluctuations and including partial correlation between the velocities. The influence of this new modeling approach is tested within a 2D spray simulation by comparing the Sauter mean diameters observed to the ones obtained by employing the modeling approaches proposed in the literature which do not consider any Stokes number effects.The reduced collision velocites in the new modeling lead to higher values for Sauter mean diameters in the spray.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5041