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Journal ArticleDOI

Characterization of a prefilming airblast atomizer in a strong swirl flowfield

01 Sep 2008-Journal of Propulsion and Power (American Institute of Aeronautics and Astronautics (AIAA))-Vol. 24, Iss: 5, pp 1124-1132
TL;DR: In this paper, an experimental investigation of the characteristics of a hollow cone prefilming airblast atomizer in a strong swirling air flow is presented, where the measured quantities include the spray cone angle by planar imaging, pattemation using planar laser-induced fluorescence, planar droplet velocity field using two-component particle image velocimetry, and droplet size and velocity distributions using a phase Doppler particle-size analyzer and laser Dopplers.
Abstract: Most gas turbine engines in service use a prefilming airblast atomizer in combination with strong swirling flow. An experimental investigation of the characteristics of a hollow cone prefilming airblast atomizer in a strong swirling air flow is presented in this paper. The measured quantities include the spray cone angle by planar imaging, pattemation using planar laser-induced fluorescence, planar droplet velocity field using two-component particle image velocimetry, and droplet size and velocity distributions using a phase Doppler particle-size analyzer and laser Doppler velocimetry. Patternation of the spray field showed regions of high droplet concentration and volume flux fluctuations in various cross-sectional planes. The investigation revealed the presence of droplets of narrow size range up to 25 μ around the axis of the atomizer in the central toroidal recirculation zone of the swirler. The presence of vortical structures entraining the droplets is observed from the instantaneous velocity vector fields. The velocity data shows entrainment of the droplets in the central toroidal recirculation zone. Examining the size and the velocity data reveals that the centrifugal action of the swirling air flowfield from the atomizer carries the bigger droplets outward, toward the periphery of the spray.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the internal atomization characteristics of a gas turbine fuel injector are investigated comprehensively using various laser flow diagnostic techniques using a phase Doppler interferometer at different stages of the injector.
Abstract: The internal atomization characteristics of a practical gas turbine fuel injector are investigated comprehensively using various laser flow diagnostic techniques The injector consists of a pilot spray surrounded by a primary swirl air, with the spray impinging on a venturi prefilmer to form a liquid film that accumulates into a rim at the venturi tip, which in turn is sheared by a counter-rotating secondary swirl air The atomizer geometry is modularized into different configurations to access the internal flow field The quantitative measurements made are with a phase Doppler interferometer at different stages of the injector and time-resolved volume or planar laser induced fluorescence (TR-V/PLIF) imaging The different internal atomization characteristics such as the liquid film thickness variation, size distribution of craters formed by primary spray droplets impinging on the liquid film, rim thickness at the venturi tip, and droplet size and velocity distribution at different stages are measured It is found that the film dynamics is influenced by the droplet splashing and the shearing action of the primary air The liquid rim at the venturi tip is the major source of droplets at the injector exit rather than the liquid film The unsteady evolution of the multiphase flow inside the injector is dictated by the precessing vortex core of the primary swirl However, the atomization process is mainly influenced by the central toroidal recirculation zone of the primary swirl flow and the counter-rotating shear layer acting on the accumulated liquid rim at the venturi tip

21 citations

Journal ArticleDOI
01 Jan 2017
TL;DR: In this article, a simplex nozzle is arranged at the center of two coaxial counter-rotating radial air flow swirlers, and two transparent coaxial tubes are attached, one each to the primary and secondary air swirl paths.
Abstract: A coaxial twin counter-rotating air swirl prefilming injector with necessary optical access, is developed to visualize and quantify its internal fluid dynamics. This research injector consists of a simplex nozzle arranged at the center of two coaxial counter-rotating radial air flow swirlers, and two transparent coaxial tubes are attached, one each to the primary and secondary air swirl paths. Spray from the simplex nozzle is swirled by the primary air and impinges on the inner tube—the prefilmer, undergoes filming, and convects to the tube tip to form a liquid rim, which is sheared by the counter-rotating swirl into finer droplets. Stage-wise phase Doppler particle analyzer measurements indicate the final spray to be much finer than the simplex nozzle spray after undergoing the above processes. Time resolved laser induced fluorescence (TR-LIF) imaging techniques are applied to visualize the wall filming and primary atomization inside the injector. The simplex nozzle spray velocity under the influence of air swirl flow is measured using stereo-particle image velocimetry. The precessing vortex core from the primary swirl imparts a precessing motion to the simplex spray, which in turn induces a non-uniform filming on the prefilmer. The droplet impingement on the prefilmer leads to splashing and crater formation on the surface. The crater size distribution is obtained and compared to the droplet size of the injector spray before impingement. The film thickness variation on the prefilmer surface and the rim thickness are estimated from planar LIF experiments along with a long distance microscope. The thickness of the liquid rim is identified as a major factor in determining the final droplet size at the injector exit. These are correlated to SMD at the injector exit at different air flow rates.

18 citations

Journal ArticleDOI
TL;DR: In this paper, the authors analyzed different modes of annular liquid sheets experimentally in an advanced hybrid injector, which uses both pressure swirl and air momentum to impart instability into the sheet.
Abstract: Disintegration of annular liquid sheets is an important field of study that plays a crucial role in engine combustion. The focus of this study is to analyze different modes of sheets experimentally in an advanced hybrid injector, which uses both pressure swirl and air momentum to impart instability into the sheet. Apart from measurement of certain macroscopic spray physical parameters like breakup length and sheet width, the images for different sheet profiles were processed to obtain fractal dimensions, temporal frequency, and different orthogonal modes using proper orthogonal decomposition. A moderate airflow is seen to create a stable liquid sheet with increased breakup length, whereas higher airflows at low liquid flows create an air-blast type of spray with disintegration very close to the nozzle. The latter shows dominance of multiple smaller temporal frequencies with relatively lower power spectral densities. A spray with high liquid flow and relatively low airflows shows a longer and wider sheet w...

17 citations


Additional excerpts

  • ...In airblast atomizers, the swirl is generally provided with the help of swirl vanes, the angle of which decides the degree of swirl [7]....

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Journal ArticleDOI
TL;DR: In this article, the effect of the flow field on spray characteristics in the near field of an atomizer was analyzed using phase Doppler Particle Analyzer (PDPA) technique.

14 citations

Dissertation
01 Nov 2014
TL;DR: In this article, an evaluation of Lagrangian-based, discrete-phase models for multi-component liquid sprays encountered in the combustors of gas turbine engines is considered, in particular, spray modeling capabilities of the commercial software, ANSYS Fluent, was evaluated.
Abstract: Evaluation of Liquid Fuel Spray Models for Hybrid RANS/LES and DLES Prediction of Turbulent Reactive Flows Ali Afshar Masters of Applied Science Graduate Department of Aerospace Engineering University of Toronto 2014 An evaluation of Lagrangian-based, discrete-phase models for multi-component liquid sprays encountered in the combustors of gas turbine engines is considered. In particular, the spray modeling capabilities of the commercial software, ANSYS Fluent, was evaluated. Spray modeling was performed for various cold flow validation cases. These validation cases include a liquid jet in a cross-flow, an airblast atomizer, and a high shear fuel nozzle. Droplet properties including velocity and diameter were investigated and compared with previous experimental and numerical results. Different primary and secondary breakup models were evaluated in this thesis. The secondary breakup models investigated include the Taylor analogy breakup (TAB) model, the wave model, the Kelvin-Helmholtz Rayleigh-Taylor model (KHRT), and the Stochastic secondary droplet (SSD) approach. The modeling of fuel sprays requires a proper treatment for the turbulence. Reynolds-averaged Navier-Stokes (RANS), large eddy simulation (LES), hybrid RANS/LES, and dynamic LES (DLES) were also considered for the turbulent flows involving sprays. The spray and turbulence models were evaluated using the available benchmark experimental data.

6 citations


Cites background from "Characterization of a prefilming ai..."

  • ...33 Comparison of experimental and numerical results for axial velocity [13]....

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  • ...34 Comparison of experimental and numerical results for radial velocity [13]....

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  • ...35 Comparison of experimental and numerical results for tangential velocity [13]....

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  • ...8: Experimental droplet axial velocity [13]....

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  • ...8 Experimental droplet axial velocity [13]....

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References
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Book
11 Jun 2002
TL;DR: In this paper, the authors present a practical guide for the planning, performance and understanding of experiments employing the PIV technique, which is primarily intended for engineers, scientists and students, who already have some basic knowledge of fluid mechanics and nonintrusive optical measurement techniques.
Abstract: This practical guide intends to provide comprehensive information on the PIV technique that in the past decade has gained significant popularity throughout engineering and scientific fields involving fluid mechanics. Relevant theoretical background information directly support the practical aspects associated with the planning, performance and understanding of experiments employing the PIV technique. The second edition includes extensive revisions taking into account significant progress on the technique as well as the continuously broadening range of possible applications which are illustrated by a multitude of examples. Among the new topics covered are high-speed imaging, three-component methods, advanced evaluation and post-processing techniques as well as microscopic PIV, the latter made possible by extending the group of authors by an internationally recognized expert. This book is primarily intended for engineers, scientists and students, who already have some basic knowledge of fluid mechanics and non-intrusive optical measurement techniques. It shall guide researchers and engineers to design and perform their experiment successfully without requiring them to first become specialists in the field. Nonetheless many of the basic properties of PIV are provided as they must be well understood before a correct interpretation of the results is possible.

4,811 citations

Journal ArticleDOI
TL;DR: In this article, a detailed program of research on airblast atomization carried out using a specially designed atomizer in which the liquid is first spread into a thin sheet and then exposed on both sides to high velocity air.
Abstract: This thesis reports the results of a detailed programme of research on airblast atomization carried out using a specially designed atomizer in which the liquid is first spread into a thin sheet and then exposed on both sides to high velocity air. The primary aim of the investigation was to examine the influence of air and liquid properties on atomization quality. The work was divided into four main phases:- (1) The first phase was confined to the effects of liquid properties, namely viscosity, surface tension and density on mean drop size. Special liquids were produced to study the separate effect of each property on atomization quality. They presented a range of values of viscosity from 1.0 to 124 centipoise, while surface tension and density were varied between 26 and 73.5 dynes/cm and 0.8 and 1.8 gm/cm3 respectively. Atomizing air velocities covered the range of practical interest to the designers of continuous combustion systems and varied between 60 and 125 m/sec.(2) To obtain experimental data on the influence of air properties, notably air density, on mean drop size, the air temperature was varied between 23 and 151°C at atmospheric pressure in one series of experiments, while a separate study on the effect of air pressure on atomization quality was undertaken, where tests were conducted at constant levels of air velocity and temperature, using a range of liquid flows from 5 to 30 gm/sec, at various levels of air pressure between 1 and 8.5 atm. (3) In order to provide a comprehensive picture of airb1ast atomizer performance over a wide range of conditions the separate effects of varying air velocity, liquid flow rate, and hence atomizing air/liquid mass ratio on SMD were examined. This study enabled a better understanding of the effects of changes in operation on the atomizer's performance. (4) In all three phases above, velotities of both inner and outer atomizing air streams were kept equal. This last phase was aimed at studying the effect of varying the velocity between the inner and outer air streams. Best atomization quality was achieved when 65% of the total atomizing air was flowing through the outer stream. A detailed description of the light-scattering technique for drop size measurement is included. A discussion on the importance of the results obtained and their direct relevance to the design of airblast atomizers is given. A dimensional analysis and inspection of all the data obtained on the effects of air and liquid properties on atomization quality showed that over the following range of conditions: Liquid viscosity 1.0 to 44 centipoise Liquid surface tension 26 to 73.5 dynes/cm Liquid density 0.78 to 1.5 gm/cm³ Air velocity 70 to 125 m/sec Air temperature 20 to 151 °c Air pressure 1.0 to 8.5 kgf/cm² . Air/liquid ratio 2 to 6 Cont

155 citations


"Characterization of a prefilming ai..." refers background in this paper

  • ...Rizkalla and Lefebvre [3] investigated the effects of both air and liquid properties on atomization quality....

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01 Jan 1977
TL;DR: In this paper, the influence of initial liquid film thickness on mean drop size and drop-size distribution was examined using two specially designed airblast atomizers, which were constructed to produce a flat liquid sheet across the centerline of a two-dimensional air duct with the liquid sheet exposed on both sides to high velocity air.
Abstract: The influence of initial liquid film thickness on mean drop size and drop-size distribution was examined using two specially designed airblast atomizers. Both were constructed to produce a flat liquid sheet across the centerline of a two-dimensional air duct with the liquid sheet exposed on both sides to high velocity air. In one case a thin film of uniform thickness was produced by injecting the liquid through a porous plate located just upstream of the atomizing edge. The film thickness, t, was then measured by a needle contact device. In the second design the fuel entered the air stream through a thin slot whose height could be adjusted accurately to vary and control the initial film thickness. Drop sizes were measured by the well-established light-scattering technique. From analysis of the processes involved, and from correlation of the experimental data, it was found that high values of liquid viscosity and liquid flow rate result in thicker films. It was also observed that thinner liquid films produce better atomization, according to the relationship, SMD ∝ t0.38 .

103 citations

Journal ArticleDOI
TL;DR: In this paper, the influence of initial liquid film thickness on mean drop size and drop-size distribution was examined using two specially designed airblast atomizers, which were constructed to produce a flat liquid sheet across the centerline of a two-dimensional air duct with the liquid sheet exposed on both sides to high velocity air.
Abstract: The influence of initial liquid film thickness on mean drop size and drop-size distribution was examined using two specially designed airblast atomizers. Both were constructed to produce a flat liquid sheet across the centerline of a two-dimensional air duct with the liquid sheet exposed on both sides to high velocity air. In one case a thin film of uniform thickness was produced by injecting the liquid through a porous plate located just upstream of the atomizing edge. The film thickness, t, was then measured by a needle contact device. In the second design the fuel entered the air stream through a thin slot whose height could be adjusted accurately to vary and control the initial film thickness. Drop sizes were measured by the well-established light-scattering technique. From analysis of the processes involved, and from correlation of the experimental data, it was found that high values of liquid viscosity and liquid flow rate result in thicker films. It was also observed that thinner liquid films produce better atomization, according to the relationship, SMD ∝ t0.38 .

103 citations