Begell House
Atomization and Sprays
Atomization and Sprays
1044-5110
6
6
1996
THE STABILITY CURVE OF NEWTONIAN LIQUID JETS
This article reports an experimental investigation on the disintegration of cylindrical jets through a study of the stability curve. We are interested mainly in the behavior of low-velocity jets in order to understand the development of the critical point, the first maximum on the stability curve. The experimental results obtained for a jet of water under varying ambient pressures show that the critical point is not due to the effect of the aerodynamic forces for our working conditions. A detailed comparison with other experimental measurements and with predictions deduced from models available in the literature is carried out and suggests a classification of the jet behavior according to the ratio ρ*G /ρG, where the critical density ρ*G is a new jet parameter that is a function of the Ohnesorge number and of the length-to-diameter nozzle ratio. A new modification of Weber's equation is suggested here in order to predict the critical velocity in any situation. The new model, tested for the experimental situations studied in the present article, calculate critical velocity in good agreement with the experimental measurements.
S.
Leroux
URA 230 CNRS/CORIA, Mon-Saint-Aignan Cedex, France
Christophe
Dumouchel
CORIA−UMR 6614, Normandie Universite, CNRS, Universite et INSA de Rouen, France
M.
Ledoux
CORIA-UMR CNRS 6614, Universite de Rouen, Site du Madrillet Avenue de l’Universite, BP12 76801 Saint Etienne du Rouvray cedex, France
623-647
THREE-DIMENSIONAL INSTABILITY OF VISCOUS LIQUID SHEETS
The instability of a viscous liquid sheet issued in an inviscid gas medium is investigated. The dispersion relations between the growth rate and wave number of both symmetric and antisymmetric disturbances are derived and solved numerically. The effects of Weber number, gas-to-liquid density ratio, and Ohnesorge number on the growth rates of two- and three-dimensional disturbances are studied. It is observed that at low Weber number, two-dimensional disturbances always dominate the instability of symmetric and antisymmetric waves. When the Weber number is high, long-wave three-dimensional symmetric disturbances have a higher growth rate than their two-dimensional counterparts, while the opposite is true for antisymmetric disturbance. For short waves, both two- and three-dimensional disturbances grow at approximately the same rate. Increasing the gas-to-liquid density ratio or decreasing the Ohnesorge number enhances the departure in the growth rates of two- and three-dimensional symmetric disturbances of long wavelength. Both the maximum growth rate and the dominant wave number increase with Weber number and density ratio but decrease with Ohnesorge number.
E. A.
Ibrahim
Mechanical Engineering Department, Tuskegee University, Tuskegee, Alabama 36088,USA
E. T.
Akpan
Mechanical Engineering Department, Tuskegee University, Tuskegee, Alabama, USA
649-665
DEFORMATION AND BREAKUP OF DROPS BY AERODYNAMIC FORCES
An analysis of experimental data on the critical conditions of drop breakup by aerodynamic forces is given. Possible causes of divergence among data on the critical Weber number, Wec, obtained by different authors is discussed. It is shown that the most important of these causes is incorrect technique for determining Wec (at the point of breakup), and disregarding the influence of the rate of change of the flow action upon the drop. Thorough experimental investigation of peculiarities of drop fragmentation under critical and over-critical conditions was carried out. Temporal characteristics of the breakup process and the mean size of fragments being formed is measured. Generalizing formulas for Wec, the induction time, and the period of drop natural oscillations are obtained.
A. A.
Shraiber
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
A. M.
Podvysotsky
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
V. V.
Dubrovsky
Energy Institute, Ukrainian National Academy of Sciences, Kiev, Ukraine
667-692
ENTRAINED AIR AND DROPLET VELOCITIES PRODUCED BY AGRICULTURAL FLAT-FAN NOZZLES
Entrained air velocities, caused by the movement of droplets from an agricultural flat-fan nozzle through the air, have been determined in vertical and radial directions within the spray by measuring the velocities of small droplets used as tracers for air movement. The distributions of droplet volume median diameter and mean liquid velocity within the spray were also measured using a PMS laser imaging probe. The spray volume distribution in a horizontal plane below the nozzle was recorded.The radial air velocity component declined with distance from the nozzle, r, and with angle from the centerline, θ. Liquid velocity, mean droplet size, and spray volume distribution also varied with r and θ. A model developed to predict the entrained air velocities was adapted in order to be compared with the experimental results. The model predicts well the variation of entrained air velocity with r, but the measured velocity declines more quickly with θ than with the model.
P. C. H.
Miller
Silsoe Research Institute, Wrest Park, Silsoe, Bedfordshire, United Kingdom
M. C. Butler
Ellis
Silsoe Research Institute, Wrest Park, Silsoe, Beds, United Kingdom
C. R.
Tuck
Silsoe Research Institute, Wrest Park, Silsoe, Beds, United Kingdom
693-707
MODELING CAVITATING FLOWS IN DIESEL INJECTORS
A numerical model has been developed to simulate unsteady cavitation processes in plain-orifice pressure atomizers typically used in diesel engine fuel injectors. The model is implemented via solution of the two-phase Navier Stokes equations formulated with the use of a pseudo-density which varies between vapor and liquid densities. Results for sharp-edged orifices indicate that partial cavitation flows are typically periodic, with a period of the order of the orifice transit time. Reducing orifice diameter tends to inhibit both the initiation and the overall extent of the cavitated region. Even a slight rounding of the orifice inlet lip has dramatic effects on both cavitation and orifice discharge characteristics. Rounding tends to inhibit cavitation substantially, and also increases orifice discharge coefficient under both cavitated and noncavitated conditions. Finally, the cavitation field appears to develop quite rapidly (on the order of a few nozzle transit times) at the initiation of the injection process.
Yongliang
Chen
School of Aeronautics and Astronautics, Purdue University, West Lafayette, IN 47907
Stephen D.
Heister
Maurice J. Zucrow Laboratories, Department of Aeronautics and Astronautics, Purdue University, West Lafayette, Indiana, USA
709-726
Indices to Volume 6
727-736