Begell House Inc.
Atomization and Sprays
AAS
1044-5110
5
4&5
1995
ASYMPTOTIC ANALYSIS OF DROPLET COALESCENCE EFFECTS ON SPRAY DIFFUSION FLAMES IN A UNIDIRECTIONAL SHEAR LAYER FLOW
357-386
10.1615/AtomizSpr.v5.i45.10
Yoram
Tambour
Faculty of Aerospace Engineering, Technion—Israel Institute of Technology, Haifa 32000, Israel
David
Katoshevski
Environmental Engineering Unit, Ben-Gurion University of the Negev, P.O. Box 653,
Beer-Sheva 84105, Israel
An asymptotic analysis is utilized in the solution procedure of the spray governing equations in order to examine droplet coalescence effects on spray diffusion flames in a unidirectional shear layer flow. The spray diffusion flame results from an evaporating multisize (polydisperse) spray of fuel droplets suspended in one of the streams of the unidirectional shear layer flow. The droplets and their vapor spread into a co-flowing stream in which the oxidizer is contained and feed the flame. Simultaneous concurrent processes of evaporation and coalescence of fuel droplets are considered. A small parameter defined in terms of a characteristic coalescence rate is identified in the governing equations and then employed in the asymptotic solutions. Various values of this parameter are analyzed. The lateral location of the flame and its temperature are obtained here via the solution of Schvab-Zeldovich-type equations. New results are presented here for the effects of droplet coalescence on the evolution in drop size histograms, on droplet Sauter mean diameter (SMD), on vapor production across the shear layer, and on flame geometry and its temperature. The present results indicate that for relatively high coalescence rates, the lateral distributions of the droplet SMD across the shear layer assumes an S-shaped curve. It is also shown that sprays that are initially comprised of small droplets produce larger amounts of vapor and thus result in a flame that is shifted toward the oxidizer stream. On the other hand, larger droplets are formed at the expense of small droplets via coalescence. Thus, due to droplet coalescence, the resulting flame is shifted toward the fuel spray stream. The higher the coalescence rate, the smaller is the vapor production rate and the more pronounced is the shift of the flame toward the fuel spray stream. Various initial drop size histograms are considered here. The results of the present study indicate that flame location and its temperature are functions not only of the total flow rate of liquid fuel but also of the initial drop size histogram of the spray and may be affected by droplet coalescence.
HOLOGRAPHY EXPERIMENTS IN THE BREAKUP REGION OF A LIQUID SHEET FORMED BY TWO IMPINGING JETS
387-402
10.1615/AtomizSpr.v5.i45.20
B. S.
Kang
Department of Mechanical Engineering, University of Illinois at Chicago, Chicago, Illinois
Y. B.
Shen
Department of Mechanical Engineering, University of Illinois at Chicago, Chicago, Illinois
Dimos
Poulikakos
Department of Mechanical and Process Engineering,
Eidgenössische Technische Hochschule Zürich,
Zürich, Switzerland
In this article an experimental study is presented of the problem of disintegration of a liquid sheet created by two impinging jets. Utilizing a novel pulse holography technique, measurements of the size and velocity of all the liquid elements around the edge of the sheet were performed. Existing theoretical predictions on the size and shape of the liquid sheet as well as on the size distribution of the droplets around the sheet boundary were also tested against the experimental measurements. For most part, the predicted shape agreed rather well with the experimental observations, qualitatively as well as quantitatively. As the impingement velocity increased, the agreement on the maximum sheet thickness deteriorated. The experiments clearly indicated that the liquid elements are largely nonspherical and that they exhibit large size variations in the neighborhood of the same location. This behavior is not predicted by the theories, which are based on the premise that the droplets at each angular position are monodispersed.
STREAKED PARTICLE IMAGING VELOCIMETRY AND SIZING IN A SPRAY
403-416
10.1615/AtomizSpr.v5.i45.30
D. C.
Herpfer
Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, Ohio
S.
Jeng
Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, Ohio
S. M.
Jeng
Department of Aerospace Engineering and Engineering Mechanics, 745 Baldwin Hall, P.O. Box 210070, University of Cincinnati, Cincinnati, OH 45221
Streaked particle imaging velocimetry and sizer (SPIVS), a nonintrusive system for planar instantaneous measurement of two-component droplet velocity and size in complex two-phase spray flows, is demonstrated. This system upgrades traditional double-light-pulse particle imaging techniques by overlaying particle streakings on the particle image pairs. The advantages of this system are the enhanced reliability of the droplet pairing process, the identification of the time sequence between images of a droplet image pair, and the ability to measure the size of individual droplets. The resultant system can be applied to sprays with high droplet velocity gradients, droplets without preferred flow directions, and high droplet number density. The SPIVS system was demonstrated on a GE SNECMA CFM56 engine combustor dual swirl-cup atomizer. The relative droplet size and velocity distribution of this spray flow are presented in this article.
ATOMIZATION OF CROSS-INJECTING SPRAYS INTO CONVECTIVE AIR STREAM
417-433
10.1615/AtomizSpr.v5.i45.40
Kenneth D.
Kihm
Texas A&M University College Station, TX; and Micro/Nano-Scale Fluidics and Energy Transport Laboratory, University of Tennessee, Mechanical, Aerospace and Biomedical Engineering Department, Knoxville TN 37996-2210, USA
G. M.
Lyn
Department of Mechanical Engineering, Texas A&M University, College Station, Texas
S. Y.
Son
Department of Mechanical Engineering, Texas A&M University, College Station, Texas
Experimental investigations have been made for cross-injecting sprays into a convective air stream as a primary means of fuel atomization. A laser diffraction particle-analyzing technique (the Malvern system) is used assuming a Rosin-Rammler two-parameter model for the drop size distribution function. The study's varied injection parameters include the convective air flow rate, the flow rate of the injected liquid (distilled water), the orifice diameter, and measurement locations along the two-dimensional spray plane. Buckingham-PI analysis finds the correlation of dimensionless parameters. A correlation of drop Sauter mean diameter (SMD) normalized to the orifice diameter is obtained from all the experimental data as SMD/Do = 1.015 × 1019 Reg−3.5998Ref−1.8094We2.2474(x/Do)−0.6867(y/Do)1.9718
where Do is the injector orifice diameter that constitutes the length scale of Ref and of We. The air Reynolds number, Reg, is defined based on the channel hydraulic diameter. A statistical analysis of the correlation equation shows a 97.5% confidence interval and a coefficient of multiple determination, R2, of 0.94.
MULTIPOINT STATISTICAL STRUCTURE OF THE IDEAL SPRAY, PART I: FUNDAMENTAL CONCEPTS AND THE REALIZATION DENSITY
435-455
10.1615/AtomizSpr.v5.i45.50
Christopher F.
Edwards
Thermosciences Division, Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
K. D.
Marx
Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA
In this study we develop the theoretical framework required for analysis of the time-based multipoint statistics of sprays. This is accomplished in the context of the ideal spray—a random assemblage of droplets modeled as noninteracting point particles. It is shown that such a spray may be decomposed into a series of independent single-class sprays, each of which is driven by an inhomogeneous temporal Poisson process. Complete spray behavior is found by superposition of these processes. A function is derived that contains all possible information about one of these single-class sprays, the realization density. All of the customary multipoint statistics—the autocorrelation, power spectral density, fluctuation moments, etc.—may be developed from the realization density by suitable integrations over its probability space. Derivations of these quantities from the realization density are reported in a series of companion articles.
MULTIPOINT STATISTICAL STRUCTURE OF THE IDEAL SPRAY, PART II: EVALUATING STEADINESS USING THE INTERPARTICLE TIME DISTRIBUTION
457-505
10.1615/AtomizSpr.v5.i45.60
Christopher F.
Edwards
Thermosciences Division, Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
K. D.
Marx
Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA
Evaluation of the steadiness of sprays is possible using the interparticle time distribution—an easily measurable function that contains information about the expected occurrence rate of droplets in a spray. Combined with ensemble-averaging of spray realizations, the interparticle time distribution permits unambiguous classification of sprays on the basis of the time dependence of their intensity function—the probability density for droplet occurrence. Three major spray classifications are defined: steady, unsteady/deterministic, and unsteady/tochastic. Each of the two latter categories may be further refined, leading to the classifications sinusoidal, complex periodic, almost periodic, transient, strictly stationary, N-point stationary, weakly stationary, and nonstationary. Analytical expressions for the interparticle time distribution are derived for each major category of spray using the ideal spray assumptions. Using these expressions, methods are developed that permit unambiguous classification by means of time-series phase Doppler data. The classification methods (and the existence of the classifications themselves) are then demonstrated by application to data from a nominally steady kerosene spray flame.
TRANSIENT BEHAVIOR IN THE EVOLUTION OF LAMINAR MULTISIZE SPRAY DIFFUSION FLAMES
507-523
10.1615/AtomizSpr.v5.i45.70
J. Barry
Greenberg
Aerospace Engineering, Technion, Israel Institute of Technology (IIT), Haifa 32000,
Israel
I.
Shpilberg
Faculty of Aerospace Engineering, Technion—Israel Institute of Technology, Haifa, Israel
Recent experimental work by Levy and Bulzan [15] has revealed a pulsating mode of diffusional combustion for a Burke-Schumann flame setup with fuel spray injection. The gross flame pulsations are accompanied by the production of small flamelets at the tip of the main flame, which break off and disappear downstream. In an attempt to uncover the mechanism responsible for these unsteady phenomena, the evolution of a Burke-Schumann type of spray diffusion flame is examined theoretically. Full representation of transport, spray, and combustion is allowed through use of nonunity Lewis numbers for the gaseous components, local pointwise multisize droplet distribution for the spray, and a finite chemical Damkohler number based on a single global chemical reaction. It is found that under certain operating conditions the transient behavior of the spray flame exhibits the phenomenon of flame separation, even though a steady state is ultimately attained. The local polydispersity of the spray is shown to be one of the major factors affecting the appearance of the separated flamelet.