Atomization and Sprays

Published by Begell House
Online ISSN: 1044-5110
Publications
Conference Paper
This paper presents results on fabrication and testing of micromachined fuel atomizers for gas turbine engines. Pressure-swirl (simplex) atomizers are batch fabricated by bulk micromachining of silicon using deep reactive-ion-etching (RIE). The atomizers are fabricated as an array, according to a designed experiment, and the influence of the geometric features on the performance of the atomizers is studied. The atomizer design is optimized by a response surface methodology. Finally, a comparative study is done, comparing and contrasting the performance of the silicon atomizers with conventional and metallic atomizers
 
Article
Droplet size and gas velocity were measured in a water spray using a two-component Phase/Doppler Particle Analyzer. A complete set of measurements was obtained at axial locations from 5 to 50 cm downstream of the nozzle. The nozzle used was a simple axisymmetric air-assist nozzle. The sprays produced, using the atomizer, were extremely fine. Sauter mean diameters were less than 20 microns at all locations. Measurements were obtained for droplets ranging from 1 to 50 microns. The gas phase was seeded with micron sized droplets, and droplets having diameters of 1.4 microns and less were used to represent gas-phase properties. Measurements were compared with predictions from a multi-phase computer model. Initial conditions for the model were taken from measurements at 5 cm downstream. Predictions for both the gas phase and the droplets showed relatively good agreement with the measurements.
 
Article
This paper describes the experimental and numerical characterization of the capillary fuel injection, atomization, dispersion, and vaporization of liquid fuel in a coflowing air stream inside a single venturi tube. The experimental techniques used are all laser-based. Phase Doppler analyzer was used to characterize the atomization and vaporization process. Planar laser-induced fluorescence visualizations give good qualitative picture of the fuel droplet and vapor distribution. Limited quantitative capabilities of the technique are also demonstrated. A modified version of the KIVA-II was used to simulate the entire spray process, including breakup and vaporization. The advantage of venturi nozzle is demonstrated in terms of better atomization, more uniform F/A distribution, and less pressure drop. Multidimensional spray calculations can be used as a design tool only if care is taken for the proper breakup model, and wall impingement process.
 
Conference Paper
The dispersion of a Jet A-1 kerosene spray generated by plain-jet-in-crossflow injection into the inner annulus of a counter-swirling double-annular airflow was investigated experimentally. Tests were conducted at 6 bar and 12 bar ambient air pressure at 750 K air temperature and at the corresponding cold test conditions in terms of air density, with an additional excursion to very high air density (9.3 bar at 290 K). The total air velocity was 114 m/s and the fuel flow through the 0.457 mm diameter plain jet nozzle was selected so that the fuel-to-air momentum flux ratio q (=(rliq×uliq2)/(rair×uair2)) was q = 4.6 . The airflow was characterized by Laser-Doppler-Anemometry (LDA) and the spray dispersion was investigated by Phase-Doppler-Anemometry (PDA). It was found that the very small droplets generated at high pressure have such a great ability to follow the streamlines of the airflow that they remain trapped in the inner annulus, preventing the formation of a homogenous fuel-air mixture in the annular flow.
 
Conference Paper
The atomization of a cryogenic nitrogen jet has been investigated under thermodynamic conditions typical for high-pressure LOX/GH2 rocket combustors. At these cryogenic high-pressure conditions the injected fluid is near its critical point. Jet spreading angles and the variation of the centerline density downstream of the injector have been determined from density profiles obtained from spontaneous Raman measurements. The results are compared with experiments and models describing the limiting cases of gas jet atomization and the disintegration of liquid sprays.
 
Article
A formulation has been developed to describe the evaporation of dense or dilute clusters of binary-fuel drops. The binary fuel is assumed to be made of a solute and a solvent whose volatility is much lower than that of the solute. Convective flow effects, inducing a circulatory motion inside the drops, are taken into account, as well as turbulence external to the cluster volume. Results obtained with this model show that, similar to the conclusions for single isolated drops, the evaporation of the volatile is controlled by liquid mass diffusion when the cluster is dilute. In contrast, when the cluster is dense, the evaporation of the volatile is controlled by surface layer stripping, that is, by the regression rate of the drop, which is in fact controlled by the evaporation rate of the solvent. These conclusions are in agreement with existing experimental observations. Parametric studies show that these conclusions remain valid with changes in ambient temperature, initial slip velocity between drops and gas, initial drop size, initial cluster size, initial liquid mass fraction of the solute, and various combinations of solvent and solute. The implications of these results for computationally intensive combustor calculations are discussed.
 
Article
This article summarizes recent results of research on the breakup of turbulent liquid jets. The research focuses on observations of atomization phenomena of cryogenic variable-density jets at various back pressures and injection velocities. The experiments used liquid nitrogen (LN2) as simulation fluid for single-component and LN2/He for binary-component injection studies. The theoreticl assessments show that for binary and multicomponent systems a transcritical region exists where surface tension is present even at pressures above the critical pressure as long as the critical mixing temperature is not exceeded. An important finding is that when approaching the critical point (transcritical regime), capillary forces decrease and a principal change of the atomization mechanism indicated by the change of jet contour length scales and ligaments sizes takes place. A discussion of the transcritical jet breakup regime with regard to classical regimes is presented.
 
Article
A rectangular sector of a realistic axially staged gas turbine combustor of Rolls-Royce Deutschland was operated at elevated pressures. Optical measurements of the reacting two-phase flow were performed using Phase Doppler Anemometry (PDA) and two planar light sheet techniques, laser induced fluorescence (LIF) and Mie scattering. The constraints, e.g. limited optical access, combustor with several injectors in line and strong soot luminescence, affecting the optical set-up for PDA measurements are discussed. The PDA measurements were conducted at a combustor inlet pressure of p = 6 bar. With an estimated error in the size measurement of up to  = 10 % caused by the change of the refractive index, it was still possible to obtain quantitative results of the mean diameter. The error of the liquid volume concentration is higher and difficult to assess. Images of the planar Mie scattering are used as a consistency check of the PDA data. The light sheet techniques deliver supplementary information. Imaging of kerosene LIF of an isothermal spray at atmospheric pressure was used to calculate the liquid volume concentration. A comparison with results from PDA measurements revealed a good agreement. Under reacting conditions kerosene LIF was limited to qualitative information on the distribution of liquid and vaporized fuel mainly because of the temperature dependency of the fluorescence quantum yield. At higher pressure the applicability of LIF was limited by the absorption of the UV laser light in the dense spray. Imaging of the planar Mie scattered light was possible at combustor inlet pressures up to p = 20 bar, giving qualitative information on the distribution of the liquid fuel.
 
Article
An experimental study of primary breakup of turbulent liquids is described, emphasizing liquid/gas density ratios less than 500 where aerodynamics effects are important. The experiments involved multiphase mixing layers along round water jets (3.6 and 6.2 mm dia.) injected at various velocities into still helium, air and Freon 12 at pressures of 1 and 2 atm. with fully-developed turbulent pipe flow at the jet exit. Pulsed shadowgraph photography and holography were used to find conditions at the onset of breakup as well as drop properties as a function of distance from the jet exit. Two main aerodynamic effects were observed, as follows: (1) enhanced primary breakup near the onset of breakup, and (2) merged primary and secondary breakup when the Rayleigh breakup times of ligaments formed by turbulent fluctuations were longer than the secondary breakup times of similar sized drops. The predictions of phenomenological theories based on these ideas were in good agreement with the measurements.
 
Article
Improved operation of kraft recovery boilers is expected to result from knowing how to obtain a controlled, well-defined droplet size distribution issuing from the black liquor spray nozzle. Black liquor drop size data were obtained from an environmentally acceptable spray facility capable of delivering liquor at normal firing temperatures using commercial nozzles. Image analysis techniques were developed from high-speed video images which gave good two-dimensional representations of black liquor sprays. Previous work showed that black liquor sprays have a characteristic size distribution which is determined by the fluid mechanical forces breaking up the liquid sheet issuing from the nozzle. This work has centered on applying flow pulsation as an independently controlled force on the sheet breakup process in an attempt to change the drop size distribution. Experiments are described which feature controlled frequency flow pulsations. Results are presented which show the dependence of median drop size on pulsation frequencies up to 450 Hz.
 
Article
The objective of this paper is to study the feasibility of large eddy simulations of a liquid fuel injection in combustion chambers. To do so, a priori analyses of direct numerical simulations are carried out. A complete liquid jet atomization, from the injector down to the end of the liquid core, is simulated thanks to the coupling of both level-set and VOF formulations. To avoid the apparition of a subgrid term in the right hand side of the continuity equation, the choice was made to consider an incompressible formulation as far as the filtering operator is concerned. The corresponding LES transport equations and various subgrid contributions are thus presented. Results are first dedicated to the estimation of the various orders of magnitude of these subgrid terms. In a second part, classical eddy viscosity scale similarity models are tested against the prevalent ones. It appears that, contrary to a Smagorinsky formulation, the scale similarity assumption provides a better estimation of the subgrid terms. This result is found for all locations that have been considered in the jet: at the injection level or in the atomized area. The major drawback is the presence of a constant that needs to be estimated. Various values are found depending on the filter size.
 
Article
This article presents the results and analysis of the droplet impaction on a hot stainless steel surface which is in two parts. Part I of this study reported the results of analysis of high speed visualisations of droplet impaction phenomena on a stainless steel hot surface, including the characteristics of reatomized droplets that are produced at high impact Weber number. Part II, herewith, provides the results and analysis of the droplet impaction heat transfer on a hot surface. The 3.0 mm diam flat stainless steel surface was heated to temperatures of 140°C < Tw < 400°C, and water sprays were produced from a droplet generation system based on an 80 mm diam rotary cup. Droplet sizes in the range 20 µm < D < 160 µm were used, impacting with velocities 5 ms<sup>-1</sup> < U < 18 ms<sup>-1</sup> . Previous research relevant to the topic is reviewed. The main purpose of this investigation was to independently analyse the effects of hydrodynamic parameters, such as droplet size, velocity, frequency, or mass flux, at different surface temperature conditions. The heat transfer results are presented and discussed in terms of overall heat flux results, although the contribution of the natural convection and radiative heat transfer (i.e., at the "no spray" condition) is also presented separately for better understanding of the results. The heat transfer effectiveness is also discussed and presented, indicating the cooling efficiency of the impacting sprays. Heat transfer effectiveness, ef, is found to decrease with increase in mass flux, which is similar in trend to that reported by other researchers. For a given mass flux, the maximum values of ef occur at Weber number 300 < We < 500 (39-62%). For a given mass flux and Weber number, the effect of increasing droplet size is to decrease ef.
 
Article
An experimental study of primary breakup of turbulent liquids in gas/liquid mixing layers is described. The experiments involved mixing layers along large liquid jets (3.6, 6.4, and 9.5 mm dia.) injected at various velocities into still air at atmospheric pressure with fully developed turbulent pipe flow at the jet exit. Liquids studied included water, glycerol (42 percent glycerin by mass), and n-heptane. Pulsed shadowgraph photography and holography were used to find conditions where turbulent primary breakup was initiated and drop sizes and velocities after primary breakup. Drop sizes after primary breakup satisfied Simmons' universal root normal distribution and can be characterized solely by their SMD. Mass weighted mean streamwise and crosstream drop velocities after primary breakup were comparable to mean streamwise and crosstream rms fluctuating velocities in the liquid, respectively, with effects of mean velocity distributions in the jet passage reflected by somewhat lower streamwise drop velocities near the jet exit.
 
Article
An experimental study of primary breakup in the near-injector region of large diameter (5.0 and 9.5 mm) liquid jets in still air is described. Measurements involved flash photography and holography to provide flow visualization and drop size distributions for initially nonturbulent liquids (water, n-heptane and various glycerol mixtures) having various jet exit velocities. Drop sizes after primary breakup satisfied Simmons' universal root normal distribution and can be characterized solely by their SMD. The SMD increased with distance from the jet exit and then remained nearly constant within a fully-developed primary breakup region. SMD measurements in the fully-developed regime did not agree with existing expressions based on unstable surface wave growth. However, an expression based on stripping-type breakup due to boundary layer growth in the liquid along the windward side of surface waves yielded a reasonably good correlation of present SMD measurements. The nature of this primary breakup correlation implies that secondary breakup is a dominant feature of liquids/gas mixing layers.
 
Article
"February 1994." "Submitted to J. Liq. Atomization and Sprays."
 
Article
Due to intense flow recirculations and strong local depression, cavitation occurs in high-pressure Diesel injectors. As experiments are very difficult to perform for injection conditions (small length and time scales, high-speed flow, ...), 3D modeling seems to be an appropriate tool in order to better understand the flow features inside and at the exit of the injector nozzle. The purpose of this paper is to present the application of the homogeneous equilibrium modeling (HEM)approach for the simulation of cavitating flows inside a Diesel multi-hole injector. The validation of the model for typical cavitating ow configurations is presented. The HEM approach allows to reproduce different cavitation regimes observed experimentally. Indeed, numerical results obtained on a simplified injector(from Soteriou et al. 2001) agree well with experimental visualizations of cavitation and multiple flow fields. Also, the computed steady state discharge coeficients of a single hole injector are close to the measured values. Furthermore, numerical results reproduce qualitatively the experimental images of cavitation. Finally, computations of cavitating flows in a six-hole narrow angle Diesel injector, taking into account the needle displacement, are discussed. It is shown that transient injector exit conditions (i.e. uid velocity at the injector exit, void fraction, cone angle, ...) are mainly due to the cavitation collapse especially during the opening and closing of the injector needle. Therefore, transient CFD code boundary conditions have to be taken into account to improve spray atomization and combustion modeling.
 
Article
Water-spray cooling of heated surfaces is common in many industrial applications, notably steelmaking, because of its high heat dissipating ability. Quantitative information regarding the parameters affecting spray cooling is relatively scarce. The objective of this research is to obtain such information by using a specially developed experimental technique that provides steady-state cooling of a steel surface using a gas-fired burner to introduce heat. The method provides fundamental information on the spray parameters controlling heat transfer from horizontal heated surfaces for a wide range of mass flux and droplet size and velocity in the film-boiling regime. Measurements are made of the drop sizes and velocities and of the liquid mass flux in the sprays produced by full-cone pressure atomizers. Heat transfer characteristics in the range of surface temperature between 380 K and 1200 K are investigated. Comparisons are made with published data and correlations are developed for heat flux and Nusselt number in the surface temperature range from 800 to 1200 K. It is found that drop size has only a weak effect on heat transfer in these relatively dense sprays. However, droplet velocity is almost as important as mass flux, so that the product of mass flux and velocity, the impinging momentum flux of water, is the dominant parameter.
 
Article
This paper, which is in two parts, presents the results and analysis of droplet impaction on a hot stainless steel surface. Part I of this study reports the results of analysis of high-speed visualizations of droplet impaction phenomena on a hot stainless steel surface, including the characteristics of reatomized droplets that are produced at high impact Weber numbers. The investigation extends to ranges of smaller droplets and higher velocities compared with published research. Part II will then provide the results and analysis of the droplet impaction heat transfer on a hot surface. The 3.0 mm diameter flat stainless steel surface was heated to temperatures of 140°C < Tw < 400°C, and water sprays were produced from a droplet generation system based on an 80 mm diameter rotary cup. Droplet sizes in the range 20 µm < D < 160 µm were used, impacting with velocities of 5 ms-1 < U < 18 ms-1 . Previous research relevant to the topic is reviewed. Physical models for different forms of droplet breakup in different regimes are developed from the new experiments and compared with existing models. Data are presented for the droplet spreading characteristics, as well as reatomized droplet characteristics, under relatively high impact Weber number conditions (i.e., 100 < We < 750), and for different boiling regimes. These data are correlated well using equations that can be justified by physical arguments.
 
Article
Extending the ignition delay to provide moretime for mixing reduces soot formation in compression-ignition engines. However, vapor-fuel concentration measurements have shown that near-injector mixtures become too lean to achieve complete combustion, leading to a relative increase in unburned hydrocarbon emissions. Entrainment wave, which is a transient increase in local entrainment after the end of injection is a contributor to over-leaning. Although an entrainment wave can be predicted by a one-dimensional (1D) free-jet model, no previous measurements at diesel injection conditions have demonstrated conclusively its existence, nor has its magnitued been confirmed. Entrained gas velocity was measured via particle image velocimetry through a diesel jet boundary before, during, and after the injection. The entrainment computation depends on the definition of the jet boundary, which was newly proposed based on the minimum of the radial coordinate and the radial velocities. The method is robust even in the presence of axial flow gradients in the ambient gases. Prior to the end of injection, the measured entrainment rates that agree well with non-reacting steady gas-jet behavior, as wekk as with the 1D free-jet model. After end of injection, the local entrainment rate temporarily increased by a factor of 2, which is similar to the factor 2.5 increase predicted by the 1D model. However, the entrainment wave is more broadly distributed in the experimental data, likely due to confinement and/or other real-jet processes absent in the 1D model.
 
Article
The present work reports a one-dimensional model to predict the liquid length and spray penetration of diesel sprays when using blends of single-component fuels. A high-pressure liquid-vapour equilibrium has been implemented by means of fugacity coefficients, together with the hypothesis of a real-gas mixture to calculate the partial enthalpy of each component. The model has been validated in a first step by means of an experimental study using binary blends of n-decane and n-hexadecane, where the temporal evolution of the liquid length and vapor spray penetration have been measured. Results show that the model predicts adequately the spray penetration for the different fuels at various conditions. A six-component fuel has also been investigated. Results indicate that this fuel has a very similar evaporative behavior to n-hexadecane, which is confirmed by both experiments and model predictions.
 
Article
To further investigate the effect of cross-flow on the fuel spray, the characteristics of the spray were analyzed under a uniform cross-flow field by visualizing various sections. The fuel was injected into a chamber under room pressure and temperature using a valve covered orifice (VCO) nozzle. Tomographic images of the spray in a vertical and several horizontal planes were taken using a high-speed video camera. The size of the spray droplets was measured along the spray direction, as well as along the cross-flow direction. Tiny droplets, which were distributed in wavy structures, were observed in the streamwise direction in the vertical plane by the observation of successive images. In addition, under the cross-flow condition, the expansion on both sides of the spray in the vertical sections increased compared with that under the no-cross-flow condition. This expansion was quantified by measuring the projected spray angles, which were based on the spray images in the horizontal planes in the crossflow. The projected spray angles were extremely enlarged compared with that under the no-cross-flow condition. In addition, large droplets were distributed in the upstream edge of the spray according to measurements acquired using a laser diffraction size analyzer. The droplet size decreased gradually along the streamwise direction. The vortex phenomenon was observed in the upper leeward part of the spray. Moreover, the spray structure and frequency of the vortices were examined based on the tomography images in various vertical positions. This indicated that the vortices were caused by the interactions of the upper spray beam and the cross-flow.
 
Article
The purpose of this paper is to summarize important aspects related to the study of the mathematical model of internal flow and the nominal performance main parameters of the conical swirl atomizer similar to that used in the JT8 Pratt & Whitney engine. The mathematical proposed model is composed of the inviscid fluid theory of Abramovich and incompressible friction theory of Kliachko, applied to the complexity of the geometry of the inlet channels, such as the irregular cross-section area and nontangential nature with respect to the swirl chamber (geometric characteristics of the conical swirl atomizer). Computational fluid dynamics (CFD) provides additional information on internal flow characteristics of swirl atomizers, the main difficulty of which is the precise control of liquid/air. It was found that by using the volume of fluid (VoF) method and k-epsilon turbulence model (implemented in software Fluent 6.3.26), an understanding of physical phenomena can be obtained as well as better visualization of the air core and hollow-cone spray angle of the atomizer, where the computational domain is composed for three-dimensional structured grids. Experimental data and numerical simulation were used for validation of this mathematical model. These results provide elementary and worthwhile information for the practical design of swirl atomizers, in addition to cost reduction before the combustion testing phase.
 
Article
Though 3D printers have become popular for manufacturing prototypes in a number of fields, they are rarely used to make injectors due to the relatively large tolerances and surface roughnesses. The flow characteristics of a swirl injector are known to depend mainly on its geometric shape and the injection conditions. In the present research, the possibility of whether or not a 3D printing technique can be applied to manufacture a swirl injector has been examined. Using different printing directions and methods, three close-Type swirl injectors were created on a 3D printer using a light polymerized process. For each injector, cold-flow tests were conducted to measure the mass flow rates, discharge coefficients, and spray angles, while changing the injection pressures. The data obtained from the printed injectors have been compared with those from a metal injector manufactured by mechanical machining. The results show that the quality of the printed injector depended on both the printing direction and method. If one chooses a suitable method for printing a close-Type swirl injector, the injector could have a discharge coefficient within a 7.5% error and a spray angle within a 12% error.
 
Article
A gasoline fuel injector is investigated using high pressure swirl injector, spraying unleaded gasoline into air at ambient pressure and temperature. Measurements using a cycle-resolved phase Doppler anemometry methodology indicate that larger droplets are produced in the early stages of the injection and populate the head and periphery of the spray cone, which becomes essentially hollow for a period between 0.75 and 2 ms. Smaller droplets in the center of the cone attain velocities in excess of 50 m/s, while those on the edge are entrained by the recirculating head vortex. The spray becomes more homogeneous after 3 ms, with little mass flow rate variation across the cone identifiable after 4.5 ms.
 
Article
This paper presents the experimental characterization of a spray produced by a VVER-440 nuclear reactor type nozzle. Several droplet size and velocity profiles have been obtained at different pressure supplies and different heights below the outlet of the spray nozzle. Repeatability and stability have been checked. A log-normal size distribution can be fitted on the experimental results. Correlations between droplet velocities and sizes at different locations are also given, showing that for small droplet sizes (below 300 mu m) no clear size-velocity correlation exists below 0.7 m from nozzle outlet, but for larger droplets, a classical evolution of this correlation is observed. It is concluded that the experimental data obtained at 300 mm from the nozzle outlet can be used as spray boundary conditions for numerical calculations with CFD codes. The other experimental data (at 500 and 700 mm from the nozzle outlet) can serve for detailed code validation, if the correlations between sizes and velocities are considered in the validation procedure: indeed, the averaging of droplet sizes and velocities can mask some typical spray results on droplet sizes and velocities evolutions. If a good code validation of the size-velocity correlations is obtained at 500 and 700 mm from the nozzle outlet, the concerned code may then be used with good confidence to extrapolate the results at other distances (for example, 3 m, 5 m) which cannot be obtained easily experimentally.
 
Article
The aim of the present work is to study a full cone pressure swirl nozzle (pressure swirl nozzles) and its configuration on a spray header for the 700 MWe Indian Pressurized Heavy Water Reactor (IPHWR) Containment Spray System (CSS) (a FOAK system). The Reynolds number (Re) effect on coefficient of discharge (Cd), spray cone angle, SMD (D32), droplet size distribution, and droplet velocity is investigated for full cone pressure swirl nozzles. Studies are performed to optimize the nozzle configuration on the spray header and the distribution of mass flux. The mass flux density studies are carried out in patternater facilities at IIT Bombay and the Kakrapar Atomic Power Project (KAPP). Water at room temperature is used for the spray in experimental investigation. The nozzle characterization experimental studies are carried out for Re ranging from 1.43 × 10⁵ to 2.49 × 10⁵. A particle droplet image analyzer (PDIA) is used for the measurement of droplet velocity, SMD (D32), and drop size distributions. A simple CCD camera along with a diode laser and patternater software is used for the measurement of the spray cone angle. The catch and time technique is used to measure coefficient of discharge. The droplet flux distribution at different Z/Do and R/Do is also performed. Nukiyama-Tanasawa distribution and log-normal peak shifted distribution show a reasonably good confirmation with the present experimental studies.
 
Article
Gel propellants are difficult to atomize due to their high viscosity and non-Newtonian, shear-thinning behavior, especially at low gas-to-liquid mass ratio (GLR). Low GLR is prerequisite for volumelimited propulsion systems. The present study explores the possibility of atomizing viscous gel propellant, using the conventional design of an air-assist internally mixed atomizer and offers comparison with a new atomizer design in which the air injection configuration is altered. Spray visualization reveals that the conventional atomizer does not produce a well-atomized spray within the given envelope of operating conditions and the spray is characterized by the presence of unatomized gel jet at the nozzle exit. However, due to its ability to provide large shearing force, the modified design promotes complete atomization of gelled fuel. The shearing effect of air in the modified atomizer configuration is more suitable for providing a well-atomized spray for highly viscous non-Newtonian fluids. Effects of GLR and gellant concentration on spray characteristics are examined in the modified atomizer configuration. Droplet size measurements show that the smallest mean droplet size is achieved at very low GLR and high gellant concentration does not significantly affect the Sauter mean diameter.
 
Penetrating casing time vs nozzle pressure difference  
Hole depth vs nozzle pressure difference  
penetrating casing time vs nozzle diameter Fig.9 Hole depth vs nozzle diameter  
Article
Perforating with an abrasive water jet (AWJ) has some advantages over conventional perforation methods, such as larger hole diameters, no crushed zone, etc. Many investigations have been conducted on such jet perforations without ambient pressures. This paper presents the experimental results of perforation with AWJs under ambient pressures to simulate practical conditions. The authors designed a new container that is able to stand 20 MPa in order to lay the casing and natural limestone samples. In the experiments, we changed the nozzle pressure drop, nozzle diameter, standoff distance, blasting time, and ambient pressure, etc., to test their influences on the perforation depth and the time to penetration of the casing. The results show that two parameters, nozzle pressure drop and diameter, are the critical factors affecting the perforation depth. That is, the depth will increase with the pressure drop and diameter going up. But the standoff distance and ambient pressure have little effect on the depth within the range of this experiment. In addition, the casing can be penetrated normally in less than 1 min. Such results prove that abrasive water jet perforation can be used in deep wells. This research also can provide a practical reference when performing AWJ perforating operations, especially in the hydrajet multistage fracturing technology extensively applied in limestone reservoirs in recent years.
 
Article
This article reports on the spatial-temporal instability behavior of a supercritical shear layer considering the real-gas effect. The dispersion relation governing the pressure perturbation was obtained and utilized to study the spatial-temporal instability of a shear layer. The dispersion relation was solved using a shooting method. The results are presented with a view to the effects of temperature ratio, velocity ratio, oblique angle, and Mach number. It is shown that in some cases, the variation of dimensionless numbers would lead to a transition between absolute and convective instability. A large value of temperature ratio or velocity ratio would enhance absolute instability; that is, increased temperature ratio or velocity ratio can make the supercritical shear layer transit to absolutely instability. Study of the effects of the oblique angle of disturbance waves shows that in spatial-temporal mode, three-dimensional disturbances dominate over two-dimensional disturbances. Increased compressibility would damp the absolute instability of a supercritical shear layer.
 
Article
This article reports the absolute and convective instability of a cylindrical liquid jet in a co-flowing inviscid gas stream. An efficient mesh-searching method is developed to determine the absolute instability and the critical Weber number which separates the region of absolute from that of convective instability. It is found that both gas velocity and density may increase or decrease the critical Weber number and may promote or suppress the absolute instability, depending on flow conditions, and that it is the absolute rather than the relative velocity that governs the absolute instability. For Weber numbers larger than the critical values, the instability of liquid jets becomes convective. The absolute gas and liquid velocity at low Weber numbers and the relative velocity between the liquid and gas at high Weber numbers control the spatial growth rate, and may enhance significantly jet breakup process at high gas velocities. Surface tension has both stabilizing (for short waves) and destabilizing (for long waves) effects on the convective growth rate whenever there exists velocity discontinuity across the liquid-gas interface. Otherwise, it always promotes the jet instability. The gas-to-liquid density ratio shows a completely opposite effect for equal and unequal gas and liquid velocities, while liquid viscosity always has a damping effect.
 
Article
This paper theoretically investigates the dynamics of internal drop motion and presents significant conclusions with respect to the role of deformational flow in drop fragmentation at low Weber numbers. The influence of deformational flow results in a selection mechanism between "bag," "claviform," and "multimode" breakup modes. This paper and conclusions are based on both the formulated instability necessary conditions and an advanced mathematical model of an accelerating and deforming drop. The analysis takes into account the pressure and surface tension force distributions along an ellipsoidal drop surface as well as the increasing gas velocity at a drop equator, caused by the flattening. It is suggested that the gas velocity values along an ellipsoid surface are the same as for a sphere at points where the angles between the normal vector to drop surface and the stream direction are the same. The numerical solutions of derived equations are used in analyzing the mass force field formation inside an accelerating and deforming drop and two stages of this process are established. It is shown that the distortion of the inertial force field, caused by deformation, causes the selection between breakup modes This paper concludes that during the first stage the deformational flow prevails over the drop's aerodynamic entrainment. Thus, the transiency and nonuniformity of the inertial force field, which are caused by the deformation, prevent "bag" early formation and result in either a "claviform" or a "multimode" mode at the later stage.
 
Article
Determination of velocities and locations of liquid droplets formed during the atomization process of a liquid jet injected in a high-pressure air crossflow represents an essential step in the definition of appropriate boundary conditions for the elaboration and validation ofreliable numerical models. In this paper, three test cases relative to different air-to-liquid velocity ratios and air temperatures are analyzed by means ofelastic scattering imaging and particle image velocimetry (PIV). The significance of the PIV measurements, evaluated as a function of spatial position and operating conditions, was adequately high with the exception of the nearest field to the injection point, where the spray is too dense. Velocity data, measured in the axial and transversal planes, are presented along with corresponding velocity components' profiles at selected positions. Results show the rapid alignment of droplet trajectories to the airflow and the dominant role played by the airflow in determining final droplet velocities and, hence, their placement in the spray plume. The droplets close to the windward profile move parallel to the jet leading edge, whereas in the leeward region they cross the scattering intensities' isocontours. On the grounds of these results, a synthetic description of liquid droplet velocities' behavior in the different regions of the spray plume is given that represents a useful conceptual tool in the attempt to correlate physical mechanisms, underpinning atomization processes, to the observed phenomenologies.
 
Article
A computational study on the dynamics of single droplets is performed in two gas flows at moderately high Reynolds numbers. One is Poiseuille flow in which the gas is either nitrogen or helium and the other is a counterflow formed by two opposed streams of nitrogen. The focus of the study is to review the methodologies used for representing the effects of flow nonuniformity and relative acceleration on droplet motion at moderately high Reynolds numbers. The motion of the droplets is observed to be affected by flow nonuniformity and unsteadiness, characterized respectively by dimensionless parameters κ and A C, and the effects due to nonuniformity and rate of change of relative velocity are separable. It is determined that acceleration and deceleration affect the drag and lift on droplets in dissimilar ways. The lift force caused by flow nonuniformity is in the same direction as κ in Poiseuille flow, whereas it is in the opposite direction as κ in counterflow. It is noted that the radius of curvature of droplet trajectory affects lift force more strongly than drag force. Modified correlations for the drag and lift coefficients as functions of the Reynolds number and dimensionless parameters characterizing the flow nonuniformity and unsteadiness are proposed.
 
Article
Ethanol-blended gasoline fuels are penetrating the market due to the renewable nature of ethanol and an anti-knock benefit associated with ethanol's higher octane number. Although ethanol usage is already popular in gasoline engines using port fuel injection (PFI), little fundamental information is available regarding important spray parameters. To address this issue, PFI sprays were studied in an optical chamber simulating boosted intake conditions. Using a highresolution CCD camera, Mie-scattered spray images were obtained and processed to determine spray-tip penetration, mean droplet diameter, and number of droplets. The ethanol-to-gasoline ratio was varied to investigate the effect of ethanol blending on these spray parameters. Mie-scattering imaging was also performed for various intake pressures considering turbocharged or supercharged conditions. From the experiments, expected trends were observed such as increasing tip penetration and decreasing mean droplet diameter with increasing time after the start of injection. Evidence of droplet breakup and evaporation during the spray penetration was also identified from detailed analysis of mean droplet diameters and number of droplets. Unexpected trends were also observed from ethanol sprays. Despite its lower vapor pressure, higher boiling point, and higher heat of vaporization, ethanol sprays showed a lower tip penetration and smaller droplet size than gasoline. The multicomponent nature of conventional gasoline was used to explain this trend: Heavy molecules of gasoline break up and evaporate at a slower rate than ethanol. It was also found that increased ambient pressure caused a shorter spray-tip penetration due to higher ambient drag. By contrast, the mean droplet diameter was larger for higher ambient pressure because of decreased evaporation rate associated with increased saturation temperature. The fundamental information obtained in this study will help develop commercially viable ethanol-fueled engines without compromising high-power performance.
 
Article
The numerical simulation of turbulent dilute spray jet flows with poly-disperse acetone sprays is presented, where the gas-phase model includes a transported joint probability density function (PDF) of the gas velocity and the mixture fraction. The solution of the joint PDF transport equation is achieved through a hybrid Eulerian/Lagrangian Monte Carlo particle method. The simplified Langevin model and the interaction-by-exchange-with-the-mean (IEM) model are used for the velocity and scalar evolution of discrete gas particles, and additional terms account for interaction of the gas and the spray evaporation. The spray dynamics is modeled using a Lagrangian discrete parcel method for the description of droplet motion, heating, and evaporation. The interphase mass, momentum, and energy transfer are considered using the point source approximation for dilute sprays in the gas phase and through appropriate terms in the liquid phase. A convective droplet evaporation model is used, and the infinite conductivity model with consideration of non-equilibrium effects based on the Langmuir-Knudsen law is applied. Numerical results are compared with the experimental data set B of Gounder, Kourmatzis and Masri, Sydney, Australia, in terms of droplet size, liquid volume flux as well as mean and fluctuating axial droplet velocities, where the three different spray flows SP2, SP6, and SP7 with different inlet droplet loadings and turbulence levels are simulated. Generally, good agreement is observed. Moreover, the local joint PDFs of the gas velocity and the mixture fraction are presented and analyzed.
 
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Primary atomization within a transonic self-generating pulsatile three-stream injector has important industrial rele- vance; however, very few studies have explored the intricacies of these dynamic flows. Prior computational work used compressible axisymmetric (AS) models and incompressible 3D models for the purpose of obtaining spectral content and preliminary droplet size distributions, which was validated with experiments. The emphasis of the work herein shifts to compressible 3D computational models for a non-Newtonian slurry and a more inclusive computational do- main to further elucidate droplet size information. Effects of numerics, turbulence model, and geometric parameters are investigated. Lastly, links are discovered between responses in Sauter mean diameter and trends in AS model- ing metrics. As with prior air-water work and incompressible slurry simulations, higher gas inner flow rate reduced droplet size measurably. While the temporal mean droplet length scale was relatively insensitive to numerics, turbu- lence model, compressibility, and computational domain size, droplet size temporal variability responded very strongly to some of these effects. It was found that injector designs with less retraction (smaller prefilming region) produced smaller droplets and allowed increased process throughputs. Newly discovered correlation equations are provided and followed similar trends to AS work. Interestingly, it was also shown that droplet size can be correlated with spectral information from companion AS studies.
 
Article
The effect of a variable acoustic field on the evaporation characteristics of a nonreacting ethanol spray lias been investigated in a long, vertical tube using a phase Doppler particle analyzer. The parametric effect of the first, second, and third acoustic modes were studied for a constant sound pressure level, using the steady flow condition as a reference. Axial and radial profiles of Sauter mean and arithmetic mean droplet diameters, and time-resolved droplet velocities, were measured and compared for the four experimental conditions while holding the spray location fixed inside the tube. Spectral analysis of the droplet axial velocity component revealed dominant frequencies equal to the frequencies of the acoustic waves in the tube. Average droplet velocities under all four experimental conditions remained the same. Droplet diameters decreased between 13% and 31%, 15% on average, in the presence of the first and third modes, compared to steady values. The second mode had little effect on the droplet diameters because the location of the nozzle corresponded to a velocity node of the stationary acoustic field'for the second harmonic. A simple mathematical model describing the evaporation of a droplet in a pulsating flow field yielded results that agreed qualitatively well with the experimental results obtained.
 
Top-cited authors
Cameron Tropea
  • Technische Universität Darmstadt
Rolf Reitz
  • University of Wisconsin–Madison
Raul Payri
  • Universitat Politècnica de València
Marco Marengo
  • University of Brighton
Romain Rioboo
  • Euro Heat Pipes SA, Belgium