55    EXPERIMENTS IN SMALL-SCALE CAVITATION IN
ATOMIZING ORIFICE FLOWS
Steven H. Collicott. Associate Professor
Mark Henry and Haiyun Li. Graduate Students
School of Aeronautics & Astronautics
Purdue University
West Lafayette, Indiana 47907-1282
ABSTRACT
Cavitation inside of spray orifices is an inherently unsteady process which, in many cases, appears to have an effect on some properties of the spray. Experimental data on small-scale cavitation is scarce, thereby hindering development of practical numerical models. Lack of empirical
and numerical models limits spray-system design to cut-and-try exercises. Experiments in a
small-scale cavitating slot orifice are described, and image data presented to illustrate the complex flow structures present in low-pressure spray orifices.
INTRODUCTION
Cavitation within an atomizing orifice has been shown to affect the resulting spray, in some
cases in a favorable manner.1,6,9 Better understanding of the characteristics of the cavitation (inception, extent, conditions for hydraulic flip, effect of asymmetric flow, . . .) is desired to improve the performance of some spray equipment, and also to improve the design methods for
such systems. Experimental research can lead to better understanding of the physics of the phenomena and specialized experiments can produce an empirical database for specific design
needs. Numerical modeling research can produce nonempirical design tools for a range of applications. Experimental and numerical research efforts, conducted in parallel by a research group
with daily interaction, is an effective methodology for advancing both areas. Previous reports
from this group describe the numerical modeling3,4,7 and experiment geometry.8 This chapter reports on experiments to visualize and study the cavitation at the entrance to a spray orifice in a
two-dimensional flow, and examples from the numerical modeling efforts are included for comparison.
Earlier experimental efforts with optical methods applied to studying cavitation within small
orifices, regardless of the pressures involved, are few. Chaves et al." presents a number of images in the range of 200 pm diameter and L/D ■ 5, accompanied by a good discussion of the
image data, discharge coefficient, and a two-point correlative velocimetry technique. Tamaki, et
al.9 present image data from small orifices, and an brief investigation into the effects of turbulence and cavitation on the spray. Images of the cavitation within the slender circular orifices are
presented in both these works. Because of the aspect ratio (L/D) of the orifices, and that the cavitation occurs along the walls of the orifice where the refractive power of the curved glass-liquid
or glass-vapor interfaces is strongest, these are inherently difficult images to acquire and interpret. Several more papers are found for larger-sized orifices,2,5 though the scaling of those results down to diesel-injector sizes is impractical. In contrast, because the present experiment
seeks to compare with the pseudo-density numerical model of Chen and Heister,1,4,7 rather than
with an existing injector or spray nozzle, the two-dimensional slot flow with its superior optical
access is used.
The cavitating slot flow has previously been shown to be a practical geometry for generating
data for code development.8 The 2-D mean flow, the single cavitation region, and easy optical
52nd Purdue Industrial Waste Conference Proceedings. 1997, Ann Arbor Press. Chelsea, Michigan 48118. Printed in
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