Spray Characteristics of Angled Liquid Injection into Subsonic Crossflows (original) (raw)
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Airblast Spray in Crossflow – Structure, Trajectory and Droplet Sizing
This study reports results of an experimental investigation of airblast spray of water and ethanol in crossflow. Laser shadowgraphy and Particle / Droplet Imaging Analysis (PDIA) are used to derive spray trajectory and drop size information while Particle Tracking Velocimetry (PTV) is used to measure drop velocities. A new phenomenon of spray bifurcation is observed for low Gas to Liquid Ratio (GLR) cases and is attributed to the bimodal nature of drop size distribution in the resultant airblast spray. A novel correlation for spray trajectory is proposed incorporating the momentum ratio and liquid surface tension. This correlation is shown to be effective in predicting the non-linear spray trajectory over a large range of conditions for not only water but ethanol and Jet-A also. The droplet Sauter Mean Diameter (SMD) is found to increase with height from the injector wall and decrease along the crossflow direction. The effect of drag is assessed by comparing velocity of different sizes of droplets at various locations. Smaller droplets are entrained into the crossflow at much lower elevations, whereas larger droplets tend to penetrate further into the crossflow. The larger drops are found predominantly on the windward periphery of the airblast spray.
Characterization of the steady and unsteady spray structures of a liquid jet in supersonic crossflow
International Conference on Liquid Atomization and Spray Systems (ICLASS)
Characterization of the spray resulting from a 1 mm diameter liquid ethanol jet injection into a supersonic air crossflow is presented. The isentropic Mach number at the injection location is 1.94, while the momentum flux ratio is varied between 3 and 13. Steady and unsteady components of the penetration depth are retrieved using backlit imaging perpendicular to the spray at a frame rate of 20 kHz, coupled with a telecentric lens to accommodate the test section's width and ensure equal magnification through the spray's width. Spray width at specific axial locations downstream of injection is measured by imaging Mie scattered light from a planar laser sheet directed perpendicular to the flow direction so that a cross section of the spray is recorded by a camera placed at a known angle between camera axis and flow direction.
Spray characteristics of free air-on-water impinging jets
International Journal of Multiphase Flow, 2018
Characteristics of a water-on-air free impinging jets atomizer is investigated in this study by means of flow visualization using high speed photography with Phase Doppler Anemometry (PDA) to measure the droplet size and velocity. Spray structures and breakup process are illustrated with the aid of images captured for the water and air jets impinging at 45°. The breakup length of the water jet decreases with the increase of the air to liquid jet momentum flux ratio (ALMFR) and remains constant for values of ALMFR larger than 1. Divergence and deflection spray angles increase rapidly with the air to liquid momentum ratio (ALMR) and then remain constant for values of ALMR larger than 4. A larger impinging angle leads to a smaller breakup length and larger spray angles. PDA results indicate that the planar distribution of droplet size is symmetrical around the Y-axis, but not around the X-axis. Smaller droplets are located near the spray center, but their location varies for different experimental conditions, with the minimum value of D 32 = 50 µm and increasing to around 120 µm at the outer region of the spray for conditions Q L = 100 mL/min, ! = 13.5 g/min and θ = 45°. The spatially-averaged Sauter mean diameter (SMD), representing the average size of droplets over a cross section plane of a spray, is defined and it remains the same at any cross section of the spray operating with the same experimental conditions. Spatially-averaged SMD is found to decrease with the increase of ALMR. Droplet mean velocity is the largest at the position downstream of the air jet exit (14 m/s at a plane of z = 75 mm in the spray with Q L = 100 mL/min, ! = 13.5 g/min and θ = 45°) and decreases gradually with increasing distance from the point where droplets with the maximum velocity are located. The study makes up for the spray visualization of the study of a single water jet impinging on a single air jet externally, and provides more information on the spray characteristics of this injector, which will contribute to the evaluation of improved computational models and improved injector design.
Experimental Studies on Spray in a Cross Flow
Experimental investigation of the structure of spray from an air-blast atomizer emerging into a cross flowing air stream is carried out. The resultant spray dispersion and trajectory are studied with the aid of optical diagnostics. Various combinations of cross-flow air velocities and air-blast spray parameters are analysed. The shadowgraphy technique incorporating laser-induced backlighting is used to study penetration for various conditions. The resulting images are then processed and analysed for effect of various parameters on spray penetration. Decrease of cross-flow velocity and increasing of Gas to Liquid Ratio (GLR) is found to increase the penetration.
Structures of Angled Aerated-Liquid Jets in Mach 1.94 Supersonic Crossflow
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005
The structures of aerated-liquid jets injected into a supersonic crossflow have been studied experimentally. Aerated-liquid injectors with diameters of 0.020" (0.5 mm), 0.040" (1.0 mm) and 0.060" (1.5 mm) were flush mounted on the bottom plate of a supersonic wind tunnel to provide normal and angled injection. Freestream Mach number and temperature were held constant at 1.94 and 500 °F (960 °R), respectively. Water at room temperature was used as the liquid injectant and nitrogen gas used as the aerating gas. Wide ranges of test conditions for injection angle (θ), injector orifice diameter (d 0), jet-to-air momentum flux ratios (q 0), and gasto-liquid ratios (GLR), were studied. Injection angles were varied from 45° downstream to 90° (normal to freestream). Jet-to-air momentum flux was varied from 1% to 15% of the freestream and gas-to-liquid ratios from 0% (pure-liquid injection) to 10%. Shadowgraph and laser sheet illumination techniques were used for spray visualization while a phase Doppler particle analyzer (PDPA) was utilized to quantitatively measure droplet and spray plume properties. The data from all three methods were used to develop correlations for the droplet and spray plume properties for aerated-liquid jets using a linear fit of the base-10 logarithm coefficients. Correlations relating penetration height and spray plume width of the injected spray to the above listed parameters, as well as the normalized axial distance downstream of the injector, x/d 0 , were formulated based on all three measurement techniques. Results indicate that a reasonable prediction of penetration height, spray plume cross sectional area, and local equivalence ratio can be obtained from PDPA data, while other visualization techniques tend to under-predict such quantities. v AFIT/GAE/ENY/05-M07 To my Mom and Dad, without whose persistence and love I never could have achieved my goals, and whose insistence on the constant pursuit of knowledge has led me here today and will continue to drive me toward horizons beyond... vi Acknowledgments First and foremost, I would like to thank God, to whom I owe all I am and have. My parents, who have always been my biggest supporters, are also owed a great deal of thanks. I would like to express my sincere appreciation to Colonel Michael A. Heil and Mr. Parker Buckley, for allowing me to take the time each day during these past couple years to pursue my degree. I would also like to thank my coworkers in the Propulsion Directorate, for their guidance, advice, and vast wealth of knowledge. I would especially like to thank Dr. Kuo-Cheng (Steven) Lin, whose mentoring was invaluable in this effort. My appreciation also goes to Dr. Richard Anthony, who never seemed to tire of my constant Matlab questions throughout this whole process. Finally, I would like to thank my advisors, Dr. Ralph A. Anthenien and Dr. Mark R. Gruber, who were instrumental in helping to turn raw data and numbers into the written work you see before you.
Droplet size and velocity characteristics of water-air impinging jet atomizer
International Journal of Multiphase Flow, 2017
A water-air impinging jets atomizer is investigated in this study, which consists of flow visualization using high speed photography and mean droplet size and velocity distribution measurements of the spray using Phase Doppler Anemometry (PDA). Topological structures and break up details of the generated spray in the far and near fields are presented with and without air jet and for an impinging angle of 90 0. Spray angle increases with the water jet velocity, air flow rate and impinging angle. PDA results indicate that droplet size is smallest in the spray center, with minimum value of Sauter mean diameter (SMD) of 50 µm at the air flow rate of Q m =13.50 g/min. SMD of droplets increases towards the spray outer region gradually to about 120 µm. The mean droplet velocity component W along the air-jet axis is highest in the spray center and decreases gradually with increasing distance from the spray center. SMD normalized by the air nozzle diameter is found firstly to decrease with gas-to-liquid mass ratio (GLR) and air-to-liquid momentum ratio (ALMR) and then remain almost constant. Its increasing with aerodynamic Weber number indicates an exponential variation. The study sheds light on the performance of water-air impinging jets atomizers providing useful information for future CFD simulation works.
Droplet Size and Velocity Distributions of a Transient Hollow-Cone Spray for GDI Engines
Particle & Particle Systems Characterization, 2001
An experimental investigation of a gasoline direct injection (GDI) spray, emerging from an electronically controlled swirl-type injector, was carried out at an injection pressure and duration of 7.0 MPa and 3.0 ms, respectively, in an optically accessible vessel, at atmospheric pressure and ambient temperature. The temporal and spatial spray evolution was investigated in terms of global spray structure, interaction with the external gas, time-resolved droplet size and velocity distribution. The measurements were carried out with an AVL Engine Video System with a CCD camera, a frame grabber and a strobe flash triggered by the injection apparatus. Digital image processing software for the study of the global parameters of the spray was used. A particle Doppler analyzer (PDA) system was used to estimate the local droplet size and velocity as function of the radial coordinate and distance from the nozzle. A laser light extinction technique was applied to investigate the region close to the nozzle up to 5 mm.
Atomization and Sprays, 2019
The paper evaluates the interaction between atomization quality and atomization efficiency, which has not been understood, although it is commonly observed that the atomization quality of different atomizers does not improve linearly with addition of energy. The results quantify the energy exchange between the air and liquid streams of a twin water impinging jets atomizer and its consequences on atomization characteristics and explain the behavior of quality and efficiency. The liquid jet breakup length, liquid jets separation distance at the breakup region and spray angles were measured with high speed photography and the droplet characteristics, such as spatial distributions of mean droplet velocities and diameters and normalized liquid volume flux with Phase Doppler Particle Analyzer (PDPA). The results show that the breakup length decreased and the separation distance of the interacting liquid jets at the geometrical 'impingement' region increased rapidly as Air-to-Liquid Momentum Ratio (ALMR) increased and then remained constant for ALMR>9. Spray angles were different on different planes through the spray and generally decreased with increasing ALMR and were insensitive to the liquid jets impingement angle. The spatial distributions of average droplet size, velocity and normalized liquid volume flux in the sprays became elongated normal to the plane of the two liquid jets for larger liquid flow rates, in agreement with the spray angle in the near nozzle region. The spatially-averaged Sauter Mean Diameter (SMD) of the sprays quantified uniquely the atomization quality and showed, for the first time, that it did not depend on liquid jets impingement angle. The average SMD remained constant beyond ALMR=9, in agreement with the near nozzle characteristics, which was explained by the energy exchange between the two streams, which reached a maximum for ALMR=3 before reducing and remaining constant for ALMR>9. 2 The atomization efficiency was quantified from the measured spatially-averaged SMD, for the first time, according to formalisms of Lefebvre (1992) and Pizziol et al. (2018). The atomization efficiency of Pizziol et al (2018) increased with the reduction of the liquid flowrate and increase of air flowrate up to Air-to-Liquid mass flowrate Ratio (ALR) of around 0.2 beyond which further increase leads to reduction of efficiency. Although this trend did not agree with Lefebvre, the values of the atomization efficiency of Lefebvre's formalism were around 0.7% of the supplied air kinetic energy, in agreement with the measured energy exchange between the air and liquid streams up to liquid breakup, while the values of Pizziol et al. (2018) were larger, probably due to the additional energy exchange between liquid and gas during secondary ligament breakup.
Drop dynamics and size distribution in a dense spray produced by a twin-fluid atomizer
International Conference on Liquid Atomization and Spray Systems (ICLASS)
Motivated by industrial applications, the spray assessment of twin-fluid atomizers is paramount for improving their design and performance. Although several studies have addressed the spray characteristics, the coupled analysis of the droplet sizes and velocities at high flow rates is still not sufficiently understood. Therefore, the present study investigates the spray instabilities from a specific variance of a Y-jet atomizer correlated to droplet size and axial velocity distribution along the spray centerline. The atomizer was operated at Reynolds numbers in the order of 10 4 , resulting in different air-to-liquid mass ratios. For that, an experimental rig operated with air and water is available for spray analysis. Data obtained with a phase Doppler anemometer showed that the mass flow rate of both fluids is directly proportional to the velocities and inversely proportional to droplet diameters. The size-velocity correlations showed that closer to the spray, the smaller droplets had higher velocities than the bigger ones. As they flowed downstream the nozzle, the impingement between the droplets and their interaction with the surrounding air decelerated them and increased their size.
Effect of liquid entry conditions Liquid jet in crossflow – Effect of liquid entry conditions
The focus of the present article is to study the effect of liquid jet injection velocity profile on the structure of liquid jet in crossflow (JICF). The experiments are conducted over a range of liquid-to-air momentum ratios (Q ~ 3-100) and aerodynamic Weber numbers (We = 17 -89). Control over the velocity profile of the injected liquid is achieved through the usage of different L/D ratios of the nozzle of the plain-orifice atomizer. The geometrical parameter L/D is varied between 10 and 100 in order to obtain fully-developed laminar flow, transition and turbulent flow. High-speed imaging and Shadowgraphy are used to study the trajectory, dropsizing and transient behavior of the resultant spray. It is observed that the dependence of trajectory of the spray is not just limited to the momentum ratio, Q, but also requires correction factors with respect to the injection velocity profiles, which are in turn related to L/D. The trajectory for the turbulent jet is found to be lower at all times when compared to that of a laminar jet for the corresponding conditions. This behavior may be attributed to the inherent instabilities present in a turbulent jet as opposed to a perfectly laminar jet. Further, we also investigate the transient phenomena of the liquid jet breakup at different conditions with the aid of Proper Orthogonal Decomposition (POD) analysis. Distinct modes of breakup are captured for the laminar and turbulent cases.