Begell House Inc.
Atomization and Sprays
AAS
1044-5110
28
7
2018
DROPLET SHADOW VELOCIMETRY BASED ON MONOFRAME TECHNIQUE
581-598
10.1615/AtomizSpr.2018026448
Azadeh
Kebriaee
Sharif University of Technology, Tehran, 1458889694
M. J.
Akbari
Sharif University of Technology, Tehran, 1458889694, Iran
F. Abbasi
Zarrin
Sharif University of Technology, Tehran, 1458889694, Iran
particle shadow velocimetry
single frame velocimetry
LED pulsed light illumination
cost-effective velocimetry
Monoframe droplet shadow velocimetry (mf-DSV) is a cost-effective method in the quality control process of the injectors. In this method, the planar (2D) velocity of the droplets is measured by tracking the droplets in a volumetric illumination, known as shadowgraphy technique. An image with two footprints of each droplet in time lapse of two light pulses is used to determine the displacement/velocity. The mf-DSV method could be established by a much less expensive setup than the
traditional velocimetry method. A high-power LED-based light source and ordinary camera without capability of double shutter mode are the requirements of this method. In this paper, different stages of image processing including binarization, clustering and diagnostics of droplets pair, and final screening are explained in detail. The challenge of out-of-focus droplets in the shadowgraphy technique is solved by using an accurate method to predict the real size of the droplets. After analyzing the errors raised in the mf-DSV method, a number of dummy and binary images are used to verify the search algorithm for droplet pair detection. Comparing the exact velocity with, that obtained by
mf-DSV indicates that the relative error originating from overlapped droplets and their elimination for velocimetry is about 0.2%. The simultaneous measurement of velocity and diameter distributions of a pressure swirl atomizer confirms the performance of mf-DSV in droplet velocimetry and sizing,
especially in the secondary atomization with dilute conditions.
CRITICAL EVALUATION OF MOMENTUM FLUX RATIO RELATIVE TO A LIQUID JET IN CROSSFLOW
599-620
10.1615/AtomizSpr.2018027032
Scott B.
Leask
UCI Combustion Laboratory, University of California, Irvine, California
92697-3550, USA
Vincent G.
McDonell
UCI Combustion Laboratory, Department of Mechanical and Aerospace Engineering, University of California at Irvine, Irvine, CA, USA
G. Scott
Samuelsen
Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92697-3550, USA
jet in crossflow
momentum flux ratio
injection velocity
jet penetration
droplet sizing
Injecting a liquid jet into a gaseous crossflow is a common atomization technique used in propulsion and power generation systems. This has led to a substantial number of fundamental cold-flow studies analyzing the atomization characteristics and dynamics of the chosen liquid. A prevalent parameter used in many jet in crossflow works is the momentum flux ratio, q, which is formulated through
the calculation of the liquid injection velocity. This work investigates various methods of calculating liquid injection velocity that are utilized in literature, their effect on the formulation of q, and the interpretation of results and conclusions. Velocity calculated through dividing mass flow rate with the geometric orifice area and through Bernoulli's principle are evaluated using an array of injector designs. Injector diameter and length-to-diameter ratio, L/d, are varied to test the generality of the interpretation of results. Basing results on q through mass flow rate divided by geometric orifice area yields discrepancies in conclusion interpretation across the different injector designs. Additionally, this method and through using Bernoulli's principle provide different interpretations which may
cause disagreements in conclusions in previous works. A new liquid injection velocity calculation method is presented which provides consistent interpretations across the different injector designs. "Ideal" experimental data are utilized to identify the liquid jet diameter which produces a certain flow condition. This jet diameter yields an effective area to give an effective liquid injection velocity by dividing mass flow rate by the effective area. This method agrees qualitatively with injection velocity determination through the use of computational fluid dynamics.
THREE-DIMENSIONAL SIMULATIONS OF DROP DEFORMATION AND BREAKUP IN AIR FLOW AND COMPARISONS WITH EXPERIMENTAL OBSERVATIONS
621-641
10.1615/AtomizSpr.2018025948
Chao
Liang
Department of Mathematical Sciences, Michigan Technological University,
Houghton, MI 49931, USA
Kathleen A.
Feigl
Department of Mathematical Sciences, Michigan Technological University, Houghton, MI
49931, USA
Franz X.
Tanner
Department of Mathematical Sciences, Michigan Technological University, Houghton, MI
49931, USA
William R.
Case
Laboratory of Food Process Engineering, Institute of Food, Nutrition and
Health, ETH Zurich, 8092, Zurich, Switzerland
Erich J.
Windhab
Laboratory of Food Process Engineering, Institute of Food, Nutrition and
Health, ETH Zurich, 8092, Zurich, Switzerland
SEA method
drop deformation
drop breakup
bag breakup
stamen breakup
sheet-thinning breakup
stripping breakup
product drop distributions
OpenFOAMĀ®
Three-dimensional symmetric computational fluid dynamics (CFD) simulations are performed to study the deformation and breakup of water drops in an air stream at different Weber numbers. The types of drop breakup considered lie in the bag breakup, the stamen breakup, and the sheet-thinning/
stripping breakup regimes. Symmetry conditions are assumed so that only one-quarter of a drop is simulated. A fully three-dimensional simulation is first conducted to justify this symmetry assumption which is then used in the remaining CFD simulations. In order to keep the drop within
the fixed computational domain, the shifted Eulerian adaption (SEA) method has been developed.
In this method all the field values are shifted back by one mesh cell after the center of the liquid mass has moved forward by one cell, while at the same time the boundary conditions are maintained. The CFD results reflect the behavior of the different breakup regimes observed in experiments. Further, the drop size distributions of each breakup regime obtained in the simulations are quantified
by lognormal distributions. These product drop size distributions are consistent with the experimental
observations and agree with simulation results reported in the literature. Furthermore, the dimensionless breakup times are in acceptable agreement with experimental values.
PULSATING SLURRY ATOMIZATION, FILM THICKNESS, AND AZIMUTHAL INSTABILITIES
643-672
10.1615/AtomizSpr.2018026380
Wayne
Strasser
School of Engineering, Liberty University, 1971 University Blvd., Lynchburg, VA 24515
Francine
Battaglia
Advanced Simulations for Computing ENergy Transport (ASCENT) Lab, Department of Mechanical and Aerospace Engineering, University at Buffalo, NY 14260, USA
compressible flow
prefilming
VOF
acoustics
A detailed numerical study on a transonic self-sustaining pulsatile three-stream coaxial airblast injector provided new insight on turbulent pulsations that affected atomization. Unique to this investigation, slurry viscosity, slurry annular thickness, and how the annular thickness interacts with inner nozzle retraction (prefilming distance) were found to be paramount to atomizer performance.
Narrower annular slurry passageways yielded a thinner slurry sheet and increased injector throughput, but the resulting droplets were unexpectedly larger. As anticipated, a lower slurry viscosity resulted in smaller droplets. Both the incremental impact of viscosity and the computed slurry
droplet length scale matched open literature values. The use of a partial azimuthal model produced a circumferentially periodic outer sheath of pulsing spray ligaments, whereas modeling the full domain showed a highly randomized and broken outer band of ligaments. However, quantitatively
the results between the two azimuthal constructs were similar, especially farther from the injector;
therefore, it was proved that modeling a wedge with periodic circumferential boundaries can be used for screening exercises. Additionally, velocity point correlations revealed that an inertial subrange was difficult to find in any of the model permutations and that droplet length scales correlated with radial velocities. Lastly, droplet size and turbulence scale predictions for two literature cases were
presented for the first time using computational fluid dynamics.