C. Aalburg

Breakup of Round Nonturbulent Liquid Jets in Gaseous Crossflow

An experimental investigation of the primary breakup of nonturbulent round liquid jets in gas crossflow is described. Pulsed shadowgraph and holograph observations of jet primary breakup regimes, conditions for the onset of breakup, properties of waves observed along the liquid surface, drop sue and velocity properties resulting from breakup and conditions required for the breakup of the liquid column as a whole, were obtained for air crossflows at normal temperature and pressure. When combined with the earlier studies of Mazallon et al. (1999), the test range included crossflow Weber numbers of 02000, liquidgas momentum ratios of 100-8000, liquidgas density ratios of 683-1021, and Ohnesorge numbers of 0.003-0.12. The results suggest qualitative similarities between the primary breakup of nonturbulent round liquid jets in crossflows and the secondary breakup of drops subjected to shock wave disturbances (e.g., bag, multimode and shear breakup regimes are observed in both instances) with relatively little effect of the liquidgas momentum ratio on breakup properties over the present test range. Effects of liquid viscosity were also small for present observations where Ohnesorge numbers were less than 0.4. Phenomenological analyses were successful for helping to interpret and correlate the properties of primary breakup of round liquid jets in gas crossflows that were measured during the present investigation.

Primary Breakup of Turbulent Round Liquid Jets in Uniform Crossflows

An experimental investigation of the deformation and breakup properties of turbulent round liquid jets in uniform gaseous crossflows is described. Pulsed shadowgraph and holograph observations were obtained for turbulent round liquid jets injected normal to air crossflow in a shock tube. Crossflow velocities of the air behind the shock wave relative to the liquid jet were subsonic (36-90 m/s) and the air in this region was at normal temperature and pressure. Liquid injection was done by a pressure feed system through round tubes having inside diameters of 1 and 2 mm and length-to-diameter ratios greater than 100 to provide fully developed turbulent pipe flow at the jet exit. Test conditions were as follows: water and ethyl alcohol as test liquids, crossflow Weber numbers based on gas properties of 0-282, streamwise Weber numbers based on liquid properties of 1400-32,200, liquid/gas density ratios of 683 and 845, and jet exit Reynolds numbers based on liquid properties of 7100-48,200, all at conditions in which direct effects of liquid viscosity were small (Ohnesorge numbers were less than 0.12). Measurements were carried out to determine conditions required for the onset of breakup, ligament and drop sizes along the liquid surface, drop velocities after breakup, liquid column breakup as whole, rates of turbulent primary breakup, and liquid column trajectories. Phenomenological theories proved to be quite successful in interpreting and correlating the measurements.

Deformation and drag properties of round drops subjected to shock-wave disturbances

Thedeformation,drag, and breakup propertiesof round drops subjected to shock-wavedisturbanceswerestudied computationally for conditions where effects of drop evaporation were small. The objective of the study was to consider effects of liquid viscosity, liquid/gas density ratio, and drop Reynolds number that are dife cult to explore based on experiments but are representative of conditions found in practical sprays. The time-dependent incompressible and axisymmetric Navier‐ Stokes equations were solved in both the gas and liquid phases in conjunction with the level set method to determine the position of the liquid/gas interface for deforming drops. The numerical results were evaluated using earlier experimental results for the wake and drag properties of solid spheres and the deformation and drag and breakup properties of drops subjected to shock-wavedisturbances. There was good agreement between measurements and predictions. The properties of drop deformation and breakup were mainly affected by the drop drag-force/surface-tension-force ratio represented by the Weber number We and the drop liquid-viscous-force/surface-tension-forceratiorepresented by theOhnesorgenumber Oh. WhentheOhwassmall, drop deformation and breakup transitions yielded the classical deformation and breakup regime map suggested by Hinze roughly 50 years ago. However, when the Oh was large the computations revealed undesirable variations of We as a function of Oh for particular deformation and breakup regime transitions when plotted in the classical Hinzeform.An improvedapproachto handlelarge Oh conditionswasfound, however, by directlyplottingthedrop drag-force/liquid-viscous-force ratio We 1=2 /Oh, as a function of the drop surface-tension-force/liquid viscous-force ratio 1/Oh because We 1=2 /Oh is relatively independent of Oh at the regime transitions when the Oh is large. Effects of liquid/gas viscosity and density ratios on the new deformation and breakup regime map were found to be small. The Reynolds number of the gas e ow over the drop, however, was found to have a considerable effect on drop deformation and breakup properties as the low Reynolds number (<100), Stokes e ow, regime was approached. This behavior appears to be caused by the progressive increase of the drop drag coefe cient when the Reynolds number of the gas e ow becomes small, which tends to reduce drop relaxation times and thus times available for drop deformation and breakup.

Properties of Nonturbulent Round Liquid Jets in Uniform Crossflows

A computational and experimental study of the deformation and breakup properties of nonturbulent round liquid jets in uniform gaseous crossflows is described, seeking to develop numerical predictions to find these properties at conditions that are difficult to address using experiments. The time-dependent incompressible two-dimensional Navier-Stokes equations were solved in the gas and liquid phases in conjunction with the level-set method to determine the position of the liquid/gas interface of the deforming liquid jets. The computations were evaluated satisfactorily based on earlier measurements for solid circular cylinders in crossflow (recirculating wake lengths, drag coefficients, conditions for the onset of eddy shedding, and frequencies of eddy shedding) and present measurements of the properties of nonturbulent round liquid jets in crossflow (liquid jet crosstream deformation, liquid jet streamwise deformation and deflection, and breakup regime transitions). Subsequent computations to find liquid jet deformation and breakup properties revealed relatively small effects of liquid/gas density ratios on deformation and breakup regime boundaries. Small Reynolds number conditions approaching the Stokes flow regime, however, resulted in a significant increase of the resistance of liquid jets in crossflow

Breakup of Turbulent and Non-Turbulent Liquid jets in Gaseous Crossflows

An experimental and computational investigation of the primary breakup of nonturbulent and turbulent round liquid jets in gas crossflow is described. Pulsed shadowgraph and holograph observations of jet primary breakup regimes, conditions for the onset of breakup, properties of waves observed along the liquid surface, drop size and velocity properties resulting from breakup and conditions required for the breakup of the liquid column as a whole, were obtained for air crossflows at normal temperature and pressure. The test range included crossflow Weber numbers of 0-2000, liquid/gas momentum ratios of 100-8000, liquid/gas density ratios of 683-1021, Ohnesorge numbers of 0.003-0.12, jet Reynolds numbers of 300-300,000. The results suggest qualitative similarities between the primary breakup of nonturbulent round liquid jets in crossflows and the secondary breakup of drops subjected to shock wave disturbances with relatively little effect of the liquid/gas momentum ratio on breakup properties over the present test range. The breakup of turbulent liquid jets was influenced by a new dimensionless number in terms of liquid/gas momentum ratio and the jet Weber number. Effects of liquid viscosity were small for present observations where Ohnesorge numbers were less than 0.4. Phenomenological analyses were successful for helping to interpret and correlate the measurements.

Deformation and Surface Waves Properties of Round Nonturbulent Liquid Jets in Gaseous Crossflow

A computational study of the deformation and surface wave properties of nonturbulent round liquid jets in gaseous crossflow is described. The objective of the study was to consider effects of liquid viscosity, liquid/gas density ratio, and crossflow Weber number that are representative of practical sprays. Three-dimensional computations of the deformation of round liquid jets in gaseous crossflow were carried out using FLUENT software utilizing its Volume of Fluid (VOF) module. The computations were evaluated satisfactorily based on earlier measurements of the properties of nonturbulent round liquid jets in crossflow (liquid jet deformation and surface waves) and revealed three-dimensional properties of the surface waves that could not be observed by previous measurements that were taken from the side of the jet.Copyright

Primary Breakup of Round Turbulent Liquid Jets in Uniform Gaseous Crossflows

An experimental investigation of the deformation and breakup properties of turbulent round liquid jets in uniform gaseous crossflows is described. Pulsed shadowgraph and holograph observations were obtained for turbulent round liquid jets injected normal to an air crossflow in a shock tube. Crossflow velocities of air behind the shock wave relative to the liquid jet were subsonic (11-142 m/s), with the air in this region at normal temperature and pressure. Liquid injection was done by a pressure feed system through round tubes having inside diameters of 1 and 2 mm and length-to-diameter ratios greater than 100 to provide fully-developed turbulent pipe flow at the jet exit. Test conditions were as follows: water and ethyl alcohol as test liquids, crossflow Weber numbers based on gas properties of 0-282, streamwise Weber numbers based on liquid properties of 5,100-24,500, liquid/gas density ratios of 683 and 845, and jet exit Reynolds numbers based on liquid properties of 3,800-59,000, all at conditions where direct effects of liquid viscosity were small (Ohnesorge numbers were less than 0.12). Measurements were completed to determine breakup regime transitions, conditions required for the onset of breakup. ligament and drop sizes along the liquid surface, drop velocities after breakup, and rates of turbulent primary breakup. Phenomenological theories proved to be quite successful in helping to interpret and correlate the measurements, providing information needed to define initial conditions for typical numerical simulations of spray structure.

Breakup of Aerated-Liquid Jets in Supersonic Crossflows

An experimental investigation of the primary breakup of aerated-liquid jets (in the annular flow regime) in supersonic crossflow is described. Singleand double-pulsed shadowgraphy and holography were used to study properties of the liquid sheet as well as outcomes of breakup in the dense spray region near the liquid jet itself that has been inaccessible to past studies using phase Doppler particle analyzers. The results show that the underexpanded internal gas phase forces the liquid sheet into a conical shape upon ejecting from the nozzle exit. Surface breakup along both the downstream and the upstream sides of the jet as well as increased breakup times of the liquid core as compared with pure-liquid jets in subsonic crossflows suggest weak aerodynamic effects of the crossflow near the jet exit. Surface velocities of the liquid sheet were measured and used to develop correlations for the liquid sheet thickness. Sizes of ligaments and drops were measured along the liquid surface and were found to have constant diameters of 30 μm and 40 μm, respectively, that were independent of the wide ranges of aeration levels, A.B. Modine Professor, Department of Aerospace Engineering, Fellow AIAA, Corresponding author, Tel.: +1-734-764-7202; Fax: +1-734-936-0106; E.mail: gmfaeth@umich.edu (G.M. Faeth). liquid/gas momentum flux ratios, nozzle diameters and liquid properties considered during the present investigation. Drop size distributions satisfied Simmons’ universal root-normal drop-size distribution function with a relatively constant ratio of MMD/SMD=1.07.

An Experimental Investigation of the Laminar Flamelet Concept for Soot Properties

The soot properties of round, nonbuoyant, laminar jet diffusion flames are described, based on experiments at microgravity carried out on orbit during three flights of the Space Shuttle Columbia, (Flights STS-83, 94 and 107). Experimental conditions included ethyleneand propane-fueled flames burning in still air at an ambient temperature of 300 K and ambient pressures of 35-100 kPa. Measurements included soot volume fraction distributions using deconvoluted laser extinction imaging, and soot temperature distributions using deconvoluted multiline emission imaging. Flowfield modeling based on the work of Spalding is presented. The present work explores whether soot properties of these flames are universal functions of mixture fraction, i.e., whether they satisfy soot state relationships. Measurements are presented, including radiative emissions and distributions of soot temperature and soot volume fraction. It is shown that most of the volume of these flames is bounded by the dividing streamline and thus should follow residence time state relationships. Most streamlines from the fuel supply to the surroundings are found to exhibit nearly the same maximum soot volume fraction and temperature. The radiation intensity along internal streamlines also is found to have relatively uniform values. Finally, soot state relationships were observed, i.e., soot volume fraction was found to correlate with estimated mixture fraction for each fuel/pressure selection. These results support the existence of soot property state relationships for steady nonbuoyant laminar diffusion flames, and thus in a large class of practical turbulent diffusion flames through the application of the laminar flamelet concept.

INVESTIGATION OF NONBUOYANT LAMINAR JET DIFFUSION FLAMES: A PARADIGM FOR SOOT PROCESSES IN TURBULENT FLAMES

The structure and soot properties of steady nonbuoyant round laminar jet diffusion flames at microgravity were studied based on measurements obtained on orbit during three flights of the Space Shuttle Columbia (Flights STS-83, 94 and 107). The test conditions included ethylene- and propane-fueled flames burning in still air at ambient temperature of 300 K and ambient pressures of 35-130 kPa, for jet exit diameters of 0.40- 2.70 mm and jet exit Reynolds numbers of 46-1186, to yield steady nonbuoyant round laminar jet diffusion flames with most of the flames near the laminar smoke- point. The first phase of the study involved evaluation of the classical analysis of the structure of steady nonbuoyant round laminar jet diffusion flames due to Spalding (1979), after empirically extending it to account for the presence of luminosity due to the presence of soot within the flames. It was found that the extended Spalding (1979) analysis provided excellent predictions of the flame shape properties of the test flames when radiative heat losses were small so that quenching and flame-tip opening were avoided. This analysis also shows that flame properties are identical functions of time for nonbuoyant laminar *