Liquid breakup at the surface of turbulent round liquid jets in still gases (original) (raw)

Turbulent primary breakup of round and plane liquid jets in still air

40th AIAA Aerospace Sciences Meeting & Exhibit, 2002

The formation of drops at the surface of turbulent liquids, e.g., turbulent primary breakup, was studied experimentally. Pulsed shadowgraphy and holography were used to observe the properties of the liquid surface and the drops formed by turbulent primary breakup. Measured properties included liquid surface velocities, conditions at the onset of ligament and drop formation, ligament and drop sizes, ligament and drop velocities and rates of drop formation. Phenomenological theories were used to help interpret and correlate the measurements. Present results show that the onset of ligament formation occurs once the kinetic energy of the turbulent eddies that form the ligaments exceeds the required surface tension energy of a ligament of comparable size. Subsequently, the onset of drop formation occurs once drops form at the tips of ligaments due to Rayleigh breakup. This same mechanism controls the subsequent variation of drop sizes due to turbulent primary breakup as a function of distance from the jet exit. In addition, ligament and drop velocities were associated with mean and fluctuating velocities of the liquid, and rates of drop formation could be expressed by surface efficiency factors defined as the fraction of the maximum cross stream liquid mass flux. B let-Water 13.5 Water 7.1 Round free jet: Water 8.0 Water 4.8

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

44th AIAA Aerospace Sciences Meeting and Exhibit, 2006

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. Nomenclature d i = streamwise jet diameter at onset of drop formation d j = liquid jet diameter at jet exit d li = diameter of ligaments at liquid jet surface d p = diameter of drops formed by primary breakup Oh = Ohnesorge number, µ L /(ρ L d j σ) 1/2 q = flow momentum ratio, ρ L v j 2 /(ρ G u ∞ 2 ) Re = Cross stream Reynolds number, ρ G u ∞ d j /µ G Re Ld = liquid jet Reynolds number, ρ L V

Primary Breakup of Turbulent Round Liquid Jets in Uniform Crossflows

AIAA Journal, 2007

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.

Primary Breakup of Round Turbulent Liquid Jets in Uniform Gaseous Crossflows

43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005

Drop formation at the surface of plane turbulent liquid jets in still gases

International Journal of Multiphase Flow, 1999

An experimental study of drop formation at the free surface of plane turbulent jets in gases (i.e., turbulent primary breakup) is described. Test conditions consisted of fully-developed turbulent plane water jets injected into still air at standard temperature and pressure with Reynolds numbers of 91,000± 424,000, Weber numbers of 13,000±151,000 and Ohnesorge numbers of 0.0009±0.0012. Pulsed shadowgraphy was used to measure mean liquid surface velocities, mean and¯uctuating drop velocities after primary breakup, drop sizes after primary breakup and the location of the onset of primary breakup. Drop velocities were related to the average streamwise velocity in a relatively simple manner, while drop size properties could be related to earlier ®ndings for turbulent primary breakup of round liquid jets in still gases using hydraulic diameter concepts.

Breakup of turbulent liquid jets in still gases

30th Fluid Dynamics Conference, 1999

An investigation of the breakup lengths of. turbulent-liquid jets in still -gases is described. Different ~breakup modes were visualized and mean and fluctuating breakup lengths were measured for round turbulent free jets of water and ethanol in still air at standard temperature and pressure. Jet exit conditions were limited to non-cavitating flows with long length/diameter ratio constant area injector passages and jet exit Reynolds numbers of 6,000-140,000, Two turb.ulent liquid column breakup modes were observed: a turbulent primary breakup ,, mode observed at small Weber numbers and a bag/shear breakup mode observed at large Weber numbers. The turbulent primary breakup-mode was

Breakup of Round Nonturbulent Liquid Jets in Gaseous Crossflow

AIAA Journal, 2004

An experimental investigation of the primary breakup of round nonturbulent liquid jets in gaseous crossflow is described. Pulsed shadowgraph and holograph observations were made to determine the following breakup properties: primary breakup regimes, conditions required for the onset of ligament and drop formation, ligament and drop sizes along the liquid surface, drop velocities after breakup, rates of liquid breakup along the liquid surface, conditions required for the breakup of the liquid column as a whole, and liquid column trajectories. These observations were made for round nonturbulent liquid jets in subsonic crossflow at normal temperature and pressure. The results suggest qualitative similarities between the primary breakup of nonturbulent round liquid jets in gaseous crossflow and the secondary breakup of drops subjected to shock wave disturbances. Phenomenological analyses were effective to help interpret and correlate the new measurements of the primary breakup properties of nonturbulent round liquid jets in gaseous crossflow.

An analysis of the distortion and breakup mechanisms of high speed liquid drops

International Journal of Multiphase Flow, 1997

A study was performed of the distortion and breakup mechanisms of liquid drops injected into a transverse high velocity air jet at room temperature and atmospheric pressure. The investigation included the use of ultra-high magnification, short-exposure photography to study the three drop breakup regimes previously referred to as the bag breakup regime, the shear or boundary-layer stripping breakup regime, and the ‘catastrophic’ breakup regime. In the experiments the initial diameters of the injected diesel fuel drops were 69, 121 and 198 μm, and the transverse air jet velocity was varied from 68 to 331 m/s. The experimental conditions correspond to drop initial Weber numbers of 56, 260 and 463 for the three breakup regimes. The drop Reynolds numbers (based on gas properties) ranged from 509 to 2488. It was found that the drop breakup process occurs in two stages. During the first stage, under the action of aerodynamic pressure, the drop distorts from its undisturbed spherical shape and becomes flattened, or disk shaped, normal to the air flow direction. This feature exists in all three drop breakup regimes. A dynamic drag model that is a modified version of the DDB (Dynamic Drag and Breakup) model and accounts for the increase of both the drop's frontal area and its drag coefficient as a function of its distortion was used to analyze the drop trajectory and its distortion during the first stage of the drop breakup process. During the second stage of the drop breakup process, the three drop breakup regimes display different breakup features. In the bag breakup regime the appearance and growth of holes on the bag sheet blown out of the center of the flattened drop is the dominant reason for the breakup; in the so-called shear or boundary-layer stripping breakup regime the results indicate that bending of the flattened drop's edge under the action of aerodynamic pressure, followed by production of folds on the bent sheet results in production of ligaments aligned in the direction of the air flow; and in the ‘catastrophic’ breakup regime the growth of capillary waves on the flattened drop surfaces, combined with the bending and folding of the sheet edge makes the breakup process demonstrate ‘catastrophic’ breakup characteristics. In addition, the experimental results confirm that for drops with different sizes, the same breakup regimes appear when the Weber number is held constant, and the Reynolds number does not play a dominant role. These results thus cast considerable doubt on the validity of the widely used ‘shear’ or ‘boundary-layer stripping’ drop breakup theories in which viscous effects would be important.

Liquid breakup at the surface of turbulent round liquid jets in still gases (original) (raw)

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