Begell House Inc.
Atomization and Sprays
AAS
1044-5110
21
4
2011
MOLECULAR DYNAMICS SIMULATIONS OF RAYLEIGH AND FIRST WIND-INDUCED BREAKUP
275-281
10.1615/AtomizSpr.2011002906
Kurt F.
Ludwig
Department of Aerospace Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA
M. M.
Micci
Department of Aerospace Engineering, The Pennsylvania State University, University Park, Pennsylvania, USA
molecular dynamics
primary atomization
Rayleigh breakup
The design of liquid-fueled engines requires an understanding of the injection and atomization phenomena occurring in the combustion chamber. Traditional methods for modeling such processes are based on the Navier-Stokes equations and require an accurate knowledge of the constituent transport and material properties and an accurate equation of state. This can be particularly difficult as one approaches the critical pressures and temperatures of the constituents. Molecular dynamics is used to simulate low Reynolds number liquid injection and jet breakup. The use of molecular dynamics allows the atomization to occur "naturally," without the need for tracking phase boundaries, and intrinsically includes all physical processes, material properties, and equations of state in both subcritical and supercritical environments. Three-dimensional molecular dynamics simulations of a laminar liquid nitrogen jet injected into subcritical gaseous nitrogen have been conducted. Simulations were conducted at pressures from atmospheric to just below critical (3.38 MPa) and liquid and gas temperatures from 76 to 124 K. Jet Reynolds numbers ranged from approximately 1 to 4, and the Weber numbers based on gas density ranged from approximately 0.04 to 7.0. For the low Reynolds and Weber number regime Rayleigh breakup is reproduced with the resulting drop sizes matching Rayleigh theory. In addition, the effect of ambient pressure on the simulated jet breakup length agrees well with general trends. Satellite drop formation was also observed. The first-ever simulations of the onset of the first wind-induced breakup regime can be seen in the cases of higher gas pressures and Weber numbers.
ON SIMULATING PRIMARY ATOMIZATION USING THE REFINED LEVEL SET GRID METHOD
283-301
10.1615/AtomizSpr.2011002760
Marcus
Herrmann
School for Engineering of Matter, Transport and Energy, Arizona State University, P.O. Box 876106, Tempe, AZ 85287-6106, USA
primary atomization; simulation; level set
The atomization process of turbulent liquid jets is as of this day not well understood. Detailed numerical simulations can help study the fundamental mechanisms in regions where experimental access and analysis is difficult. This paper presents simulation results of the primary atomization of round turbulent liquid jets injected into stagnant high-pressure air under diesel engine conditions using the refined level set grid approach. A balanced force approach is used to accurately account for surface tension forces using an interface projected curvature method to minimize erroneous spurious currents. Broken off, small-scale nearly spherical drops are transferred into a Lagrangian point particle description allowing for full two-way coupling. The physical mechanisms resulting in the initial breakup of the jet are discussed. We analyze the impact of finite grid resolution on the phase interface geometry of the injected liquid core and discuss the impact of the automatic topology-change length scale inherent in the fixed grid interface, capturing methods like the level set method. Drop size distributions resulting from primary atomization are presented, showing that grid-independent drop sizes can be achieved for liquid structures resolved by at least six grid points.
EXAMINING VISCOSITY AND SURFACE WETTABILITY ON LAMELLA LIFT DYNAMICS AND DROPLET SPLASHING
303-315
10.1615/AtomizSpr.2011002818
Henry
Vu
Department of Mechanical Engineering, University of California-Riverside, Riverside, USA , Advatech Pacific, Incorporated, Advanced Technology Division, Palmdale, California 93550, USA
Darren
Banks
Department of Mechanical Engineering, University of California-Riverside, Riverside, California 92521, USA
Guillermo
Aguilar
Department of Mechanical Engineering | Texas A&M University 102 Mechanical Engineering Office Building 3123 TAMU | College Station, TX 77843-3123
adhesion
corona
droplet
impact
pressure
splashing
spreading
The mechanisms that initiate splashing on smooth, dry surfaces are complex and differ from those on rough or prewetted surfaces. This form of splashing is greatly influenced by the surrounding gas pressure. In this work we examine the effects of droplet viscosity, surface wettability, and gas pressure on the splashing dynamics of single droplets. In previous studies droplet viscosity has been shown to both promote and inhibit splashing. In the current study this contradictory result is tested across a wide range of fluid viscosities. The impact energy required for splashing is minimized within a range of Reynolds number of ~100-500. Eventually, splashing appears to become impossible with sufficiently high viscosity due to the slowing of splashing dynamics beyond a certain time window of opportunity. Hydrophobic and hydrophilic coatings were also applied to a smooth surface in order to change the wetting characteristics of the water droplets. It was found that the hydrophilic surface required higher gas pressure (density) for splashing to occur and vice versa for the hydrophobic surface. Focusing on the spreading lamella, a momentum balance was derived with consideration of the chemical affinity or adhesive force of the liquid to the impact surface. The lamella lift from the surface was assumed to be induced by the displaced surrounding gas during spreading. This provides an explanation for the vertical velocity component of corona splashing seen on dry, smooth surfaces. In light of the lamella lift, instability within the spreading droplet is predicted to arise through Rayleigh-Taylor theory, and subsequent timescales of secondary drop formation are examined. By comparing splash thresholds on hydrophobic and hydrophilic surfaces, the effects of the adhesive force are demonstrated and quantified. The adhesive force between the lamella and impact surface plausibly explains the seemingly paradoxical effect of droplet viscosity to promote splashing for low-viscosity fluids.
CHARACTERIZATION OF FULL CONE NOZZLES
317-325
10.1615/AtomizSpr.2011003262
Boris
Kohnen
Faculty of Bio- and Chemical Engineering, Department of Mechanical Engineering, University of Dortmund, Emil-Figge-Str. 68,44227 Dortmund, Germany
Damian
Pieloth
Faculty of Bio- and Chemical Engineering, Department of Mechanical Engineering, University of Dortmund, Emil-Figge-Str. 68,44227 Dortmund, Germany
Emir
Musemic
Faculty of Bio- and Chemical Engineering, Department of Mechanical Engineering, University of Dortmund, Emil-Figge-Str. 68,44227 Dortmund, Germany
Peter
Walzel
Department of Biochemical and Chemical Engineering, Technische Universitaet
Dortmund, Emil-Figge-Strasse 68, Dortmund, 44227, Germany
full cone swirl nozzles
nozzle and spray characterization
size scaling of nozzles
drop size measurements at dense sprays
The drop size distribution (DSD) and the spray angle of full cone nozzles are measured at different atomization pressures and corresponding volumetric flow rates of water. The measurements of the DSDs were performed with laser diffraction spectrometry. The nozzles characterized here are geometrically similar models in the photo scale 1:8, 1:10, and 1:12 in relation to the original nozzle (1:1) used as the main sprayer in an industrial dust scrubber with an orifice diameter of DN = 96 mm. For all nozzles the spray pattern and flux density is characterized by means of a mechanical patternator. The overall volume frequency distribution q3(d) is calculated by a weighting procedure. The dimensionless droplet diameter dp/DN for different characteristic drop sizes( d10.3, d50.3, and d90.3) can be extrapolated to the operating conditions of the original nozzle. The spray angle of the full cone nozzles is obtained by evaluation of photographical spray images. It is found to depend on the Reynolds and the Ohnesorge number.
TARGETED MEDICAL SPRAYS STIMULATING THERAPEUTIC EFFECTS
327-348
10.1615/AtomizSpr.2011003544
Corinne S.
Lengsfeld
Department of Mechanical and Materials Engineering, University of Denver, Denver, Colorado 80208, USA
Guillermo
Aguilar
Department of Mechanical Engineering | Texas A&M University 102 Mechanical Engineering Office Building 3123 TAMU | College Station, TX 77843-3123
therapeutic sprays
medical sprays
aerosols
pulmonary drug delivery
ocular sprays
intranasal sprays
dermatological sprays
There is an enormous diversity in the number and uses of sprays in the medical community, from disinfectant strategies, drying and coating technologies, as well as target delivery of therapeutic agents to the human body. The number and range of strategies for forming these sprays is almost as varied, but in every application the droplet size distribution, particle velocity, impact dynamics, and hydrodynamic environment contribute immensely to achieving the specific performance parameters. As a result, therapeutic sprays have had difficulty fully achieving the envisioned potential. The following review article will reflect specifically on medical sprays for drug delivery to specific organs (i.e., lung, nasal, ocular, and skin) to review the current state of capabilities, but also comment on specific gaps in ability and knowledge. Our objective is to stimulate a discussion within the spray community that will result in heightened interest directed toward improved performance and efficacy.
CHARACTERISTICS OF HOLLOW CONE SPRAYS IN CROSSFLOW
349-361
10.1615/AtomizSpr.2011003586
Suraj
Deshpande
Department of Mechanical Engineering, University of Wisconsin, Madison, Wisconsin 53706, USA
Jian
Gao
Advanced Photon Source, Argonne National Laboratory, Argonne, USA; Propulsion Systems Research Lab., General Motors Global Research and Development, Warren, USA
Mario F.
Trujillo
Engine Research Center, Department of Mechanical Engineering, University of Wisconsin-Madison,
1513 University Ave., Madison WI 53706, USA
hollow cone sprays
crossflow
spray structure
and openFOAM
A qualitative and quantitative study of a hollow cone spray exposed to a cross-flowing stream of air is presented, based on the conventional Lagrangian-Eulerian point parcel spray treatment. The flow solver employs the open source library of computational mechanics solvers of OpenFOAM. Globally, the spray can be categorized by a near- and far-field region, where the demarcation makes use of the magnitude of the individual droplet drag force. In the near field the vertical spray momentum largely dominates the gas flow momentum and forces it to bend downward. Within this near field we show that two conditions−weak crossflow and strong crossflow−can be identified, depending upon the strength of crossflow in relation to the induced air motion. While this is in agreement with Ghosh and Hunt (1998), we differ in the approach taken and the spray geometry studied. In the case of a weak crossflow, the spray severely deflects the crossflow streamlines, forcing the lee side streamlines to converge toward the center of the spray. In the case of a strong crossflow, the streamlines are deflected; nevertheless, they penetrate the spray. This has a significant impact on the topology of the spray structure, which has not been previously presented. In the far field the center streamline of the spray-induced air jet agrees extremely well with a single-phase jet trajectory. This behavior is shown to be independent of grid resolution and of atomization model.