Begell House
Atomization and Sprays
Atomization and Sprays
1044-5110
3
1
1993
MATHEMATICAL MODELING OF DENSELY LOADED, PARTICLE-LADEN TURBULENT FLOWS
A mathematical model for densely loaded, particle-laden turbulent flows has been developed. The model accounts for (1) the interactions between the particles and the carrier fluid, and (2) the interactions between the particles themselves (collision). These interactions consider both mean and fluctuating levels of motion. The gas and particle flow fields are resolved in a Eulerian frame of reference. The fluid turbulence is simulated through a new k-ε model, which considers not only the damping effect of the particles on fluid turbulence but also the effects of particle collision on fluid turbulence. To validate the proposed model, a turbulent, axisymmetric gaseous jet laden with polydispersed spherical solid particles was studied. The model predictions were compared with the experimental data for polydispersed dilute and dense flows. Good agreement was achieved, which indicates the model’s capability to simulate unconfined, turbulent, densely loaded, particle-laden flows.
Mostafa A.
Rizk
Burns and Roe Services Corporation, Pittsburgh, Pennsylvania
1-27
THE LARGE-SCALE FRAGMENTATION OF THE INTACT LIQUID CORE OF A SPRAY JET
Consideration is given to the destruction of the solid core of a fast spray jet by the generation of long-wavelength instabilities that initially distort and finally break the core. This breakup mechanism is supposed to occur concurrently with the depletion of core mass by the ejection of liquid fragments along the intact core. Evidence is presented that suggests long-wavelength perturbations may be generated by two mutually dependent mechanisms: a helical or snakelike wave owing to relaxation of the velocity profile within the core; and the coherent self-induction of larger disturbances from smaller ones by vortex chaining and nonlinear interaction. These considerations have led to the formulation of a fragmentation model that employs a continuous wavelength range for the core fragmentation. Results from the model are compared with measurements in steady Diesel sprays.
Malcolm J.
Andrews
Department of Mechanical Engineering, Texas A&M University, College Station, Texas 77843
29-54
MECHANISMS OF AIR-ASSISTED LIQUID ATOMIZATION
A well-controlled experimental apparatus was used to investigate the air-assisted liquid drop atomization process. High-magnification, high-speed photography as well as conventional spray field photography was used to study the breakup of a monodisperse stream of drops injected into a transverse high-velocity air stream. The gas velocity profile, liquid drop velocity, and size were determined by laser Doppler velocimetry (LDV) and a phase Doppler particle analyzer (PDPA). The experiments gave information about the microscopic structure of the liquid breakup process, drop breakup regimes, drag coefficients of atomizing drops, breakup drop size distributions, and drop trajectories. At low gas-liquid relative velocities, the microscopic photographs confirmed the existence of bag and stripping breakup regimes. The photographs also revealed the nature of high-speed, "catastrophic," liquid atomization, which appears to be due to the development of instability waves on the liquid surface. A model based on aerodynamic liquid breakup theory was used to study the influences of the drop drag coefficient and the breakup time on the drop trajectory during the drop atomization process. Previously proposed expressions for the drop drag coefficient and the breakup time constant were tested by comparing the calculated trajectories with the measurements.
Rolf D.
Reitz
Engine Research Center, Department of Mechanical Engineering, University of Wisconsin-Madison, Wisconsin, USA
A. B.
Liu
Engine Research Center, University of Wisconsin—Madison, Madison, Wisconsin 53706
55-75
EFFERVESCENT ATOMIZATION AT LOW MASS FLOW RATES. PART I: THE INFLUENCE OF SURFACE TENSION
An effervescent atomizer that operates at flow rates of 1.5 g/s and below is shown to produce sub-70-μm Sauter mean diameter sprays at pressures below 337 kPa (40 psig) while utilizing very small amounts of atomizing air (air—liquid ratio by mass below 0.02). The mean drop sizes produced by this nozzle are found to be nearly independent of liquid viscosity for values ranging from 20 to 80 cP, while an increase in liquid surface tension from 30 to 67 dynes/cm serves to decrease mean drop size. Qualitative and quantitative descriptions of the data are obtained by modeling the atomization process as the formation of a number of ligaments at the exit orifice and their subsequent breakup using the classical analysis of Weber.
M. T.
Lund
Thermal Sciences and Propulsion Center, School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907
Paul E.
Sojka
Maurice J. Zucrow Laboratories (formerly Thermal Sciences and Propulsion Center), School of Mechanical Engineering, Purdue University, West Lafayette, Indiana, 47907-2014, USA
Arthur H.
Lefebvre
Emeritus Professor, Cranfield University, Stratford, U.K., and Purdue University, W. Lafayette, IN, USA
P. G.
Gosselin
Cincinnati, Ohio 45224
77-89
AXISYMMETRIC CALCULATIONS OF THREE-DROPLET INTERACTIONS
The present study extends the previous droplet models [1,2] to investigate numerically the system of three droplets that are moving in tandem with respect to the free flow. The purposes of this study are to study the wake effect of the lead droplet on the downstream droplets and to examine the effects of initial spacing on the total system. The effects of variable thermophysical properties, transient heating and internal circulation of liquid, deceleration of the flow due to the drag of the droplet, boundary-layer blowing, and moving interface due to surface regression, as well as relative droplet motion, are included. The results are compared with those of an isolated droplet [1] as well as those of the two-droplet system [2] to investigate the effect of the presence of the third droplet. The interaction effects from the downstream or upstream droplet are identified. The transport rates of droplets are reduced from the values for an isolated droplet, and values for the downstream droplets are profoundly less Лап those for the lead droplet. The difference in transport rates is large between the first two droplets; however, it becomes insignificant between the second and the third droplets. The modifications to the transfer correlations for an isolated droplet needed to account for the interaction effects are determined.
C. H.
Chiang
Department of Mechanical and Aerospace Engineering, University of California, Irvine, California 92664
William A.
Sirignano
Department of Mechanical and Aerospace Engineering, University of California at Irvine, USA
91-107
THE THREE-PARAMETER LOG-HYPERBOLIC DISTRIBUTION AND ITS APPLICATION TO PARTICLE SIZING
This article investigates the possibilities of representing measured size distributions in sprays in the form of a three-parameter log-hyperbolic (3P-LH) distribution. This distribution is shown to be a special case of the more general four-parameter log-hyperbolic (4P-LH) distribution but exhibits a more stable behavior in the fitting of its parameters to empirical data. The problem of parameter estimation stability using the 4P-LH distribution has been identified, and explanations are given for its causes. The 3P-LH distribution circumvents these problems while yielding a nearly equally good representation of the data for a large variety of applications. The 3P-LH distribution is therefore concluded to be a valuable means of presenting large amounts of size distribution data in a more comprehensible manner.
T.-H.
Xu
Lehrstuhl für Strömungsmechanik, Universität Erlangen-Nürnberg, Erlangen, Germany
Franz
Durst
FMP TECHNOLOGY GMBH, Am Weichselgarten 34, 91058 Erlangen, Germany
Cameron
Tropea
Technische Universität Darmstadt, Institute of Fluid Mechanics and Aerodynamics, Center of Smart Interfaces, Germany
109-124