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  • 1
    Electronic Resource
    Electronic Resource
    Spherical bubble motion in a turbulent boundary layer (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2564-2577 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Monodisperse dilute suspensions of spherical air bubbles in a tap-water turbulent vertical boundary layer were experimentally studied to note their motion and distribution. Bubbles with diameters of 0.37–1.2 mm were injected at various transverse wall-positions for free-stream velocities between 0.4 and 0.9 m/s. The bubbles were released from a single injector at very low frequencies such that two-way coupling and bubble–bubble interaction were negligible. The experimental diagnostics included ensemble-averaged planar laser intensity profiles for bubble concentration distribution, as well as Cinematic Particle Image Velocimetry with bubble tracking for bubble hydrodynamic forces. A variety of void distributions within the boundary layer were found. For example, there was a tendency for bubbles to collect along the wall for higher Stokes number conditions, while the lower Stokes number conditions produced Gaussian-type profiles throughout the boundary layer. In addition, three types of bubble trajectories were observed—sliding bubbles, bouncing bubbles, and free-dispersion bubbles. Instantaneous liquid forces acting on individual bubbles in the turbulent flow were also obtained to provide the drag and lift coefficients (with notable experimental uncertainty). These results indicate that drag coefficient decreases with increasing Reynolds number as is conventionally expected but variations were observed. In general, the instantaneous drag coefficient (for constant bubble Reynolds number) tended to be reduced as the turbulence intensity increased. The averaged lift coefficient is higher than that given by inviscid theory (and sometimes even that of creeping flow theory) and tends to decrease with increasing bubble Reynolds number. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388051
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  • 2
    Electronic Resource
    Electronic Resource
    Forces on ellipsoidal bubbles in a turbulent shear layer (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 178-188 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The objective of this research was to gain fundamental knowledge of the drag and lift forces on ellipsoidal air bubbles in water in a turbulent flow. This was accomplished by employing a cinematic two-phase particle image velocimetry (PIV) system to evaluate bubbly flow in a two-stream, turbulent, planar free shear layer of filtered tap water. Ellipsoidal air bubbles with nominal diameters from 1.5 to 4.5 mm were injected directly into the shear layer through a single slender tube. The cinematic PIV allowed for high resolution of the unsteady liquid velocity vector field. Triple-pulsed bubble images were obtained in a temporal sequence, such that the bubble size and bubble trajectory could be accurately determined. The bubble's oscillation characteristics, velocity, acceleration, and buoyancy force were obtained from the trajectory data. A bubble dynamic equation was then applied to allow determination of the time-evolving lift and drag forces acting upon bubbles within the shear layer. The results indicate that for a fixed bubble diameter (and fixed Bond and Morton numbers), the drag coefficient decreases for an increasing Reynolds number. This is fundamentally different than the increasing drag coefficient trend seen for ellipsoidal bubbles rising in quiescent baths for increasing diameter (and increasing Bond number), but is qualitatively consistent with the trend for spherical bubbles. A new empirical expression for the dependence of the drag coefficient on Reynolds number for air bubbles in tap water for both quiescent and turbulent flows is constructed herein. Finally, the instantaneous side forces measured in this study were dominated by the inherent deformation-induced vortex shedding of the bubble wake rather than the inviscid lift force based on the background fluid vorticity. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869557
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  • 3
    Electronic Resource
    Electronic Resource
    High-speed cinematography of compressible mixing layers (1994)
    Springer
    Experiments in fluids 17 (1994), S. 179-189 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Experiments are performed using high-speed film cinematography to temporally resolve compressible planar mixing layer structures using shadowgraphs and planar light sheet visualization. The technique is relatively inexpensive and allows multiple images. The time-dependent shadowgraph and Mie scattering images are documented with a rotating mirror camera operating at approximately 350 kHz. The results show the presence of large scale structures in the mixing layer which flatten as they convect downstream. Both spatial and temporal covariances have been obtained through digital image processing which yield, on average, elliptical structures with convective speeds above the isentropic prediction, and non-isotropic streamwise and transverse scalar transport fluctuations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00190915
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of plane underexpanded air jets into water (1990)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 36 (1990), S. 818-826 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An experimental and numerical investigation of the structure of plane underexpanded turbulent air jets in water was conducted to characterize their structure and mixing properties. Measurements included void fraction profiles, static pressure distributions, entrainment rates, and high speed flow visualization. A locally homogeneous flow model was also developed with compressibility effects treated using an effective adapted jet condition. Static pressure measurements confirmed the presence of a shock-wave-containing external expansion region for underexpanded air jets in water, similar to results observed for underexpanded air jets in air. In addition, the plane jets exhibited half-widths (based on void fractions) that were two to three times greater than half-widths (based on scalar properties) observed for single-phase jets. This behavior follows from the strong sensitivity of void fraction to mixing levels due to the large density ratio of the flow. Predictions of void fraction and mass entrainment were encouraging, but performance was found to be sensitive to initial conditions and effects of large-scale unsteadiness near the jet exit.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690360603
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  • 5
    Electronic Resource
    Electronic Resource
    Forces on a large cylindrical bubble in an unsteady rotational flow (1996)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 42 (1996), S. 638-648 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The full Navier-Stokes equations were employed with a single-fluid model and a front tracking scheme to study a large cylindrical bubble in a free shear layer. A general formulation based on work by Auton et al. of the hydrodynamic forces on a finite Reynolds number large bubble in an unsteady, nonuniform and rotational flow was then used to investigate the effects of nonlinear spatial and temporal gradients on dispersion. The resulting bubble dispersion in the full Navier-Stokes solution significantly differ from that by a conventional bubble dynamic equation based on linear spatial gradients and quasi-steady flow. This was due to the adjunct forces not accounted for by such a formulation, which are related to regions of high nonuniformity and unsteadiness. These adjunct forces in the drag/lift direction were correlated with rapid variations of relative bubble velocity and high gradients of the liquid velocity.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690420305
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