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  • 1
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    Surface-tension-induced mixing following coalescence of initially stationary drops (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The momentumless coalescence of drops of the same liquid, separated by an immiscible host, is studied experimentally. Observations show that for low-viscosity drops of unequal sizes, there is considerable mixing following coalescence, with the smaller drop penetrating the larger drop as a vortex. The extreme case of coalescence of a small drop with the bulk of the same liquid at a flat interface with an immiscible liquid is studied in detail. The penetration depths of small drops (1-5 mm) following coalescence are measured and correlated with theoretical predictions. It is found that in the range of the investigation, the penetration depth is proportional to the 5/4 power of drop diameter and inversely proportional to the square root of the drop viscosity.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 3; 2587-259
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Static shape and instability of an acoustically levitated liquid drop (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Dynamical aspects of a drop drastically flattened by acoustic radiation stress are considered. Its static equilibrium has been studied, starting with a dislike shape and modeling the sound field and the associated radiation stress according to this geometry. It is suggested that, at low viscosity, the ripples are capillary waves generated by the parametric instability excited by the membrane vibration, which is driven by the sound pressure. Atomization occurs whenever the membrane becomes so thin that the vibration is sufficiently intense. Buckling occurs when an existent equilibrium is unstable to a radial oscillation of the membrane because of the Bernoulli effect. The radiation stress at the rim of the flattened drop is also destabilizing and leads to horizontal expansion and subsequent breakup.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 3; 2497-251
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  • 3
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    A theoretical model for the annular jet instability (1986)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The instability of an annular gas-core liquid jet is modeled theoretically by treating the liquid layer as a membrane moving under the influences of its own inertia, surface tension, and the gaseous hydrostatic pressure difference between its two sides. Essential physical mechanisms are reconstructed without making any attempt to fit experimental data with model constants. The results compare favorably with those of experiment.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 29; 2076-208
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  • 4
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    Viscous damping of the oscillations of a rotating simple drop (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The viscous damping of the small-amplitude capillary oscillations of a rotating simple drop is calculated in the small viscosity limit. The calculation concerns the case of a liquid drop in a gaseous medium, which is relevant to the space processing of materials using acoustic levitation. The method used is that of Lamb in which the inviscid solutions of the problem are used as trial functions in the energy equation to find the damping coefficient.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids (ISSN 0031-9171); 28; 3187
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  • 5
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    The theoretical model for the annular jet instability - Revisited (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The theoretical model of Lee and Wang (1986) for the instability of an annular jet, in which the jet's liquid layer is treated as a thin liquid sheet, is examined. It is suggested that the model should be altered so that when the envelope is closing its bottleneck during collapse, the new envelope experiences a sharp pressure pulse from its gaseous core, reversing the normal velocity of the sheet enough to maintain continuous constant gas flow. Using this improved version of the model, it is shown that if the liquid velocity is high enough and the gas velocity is greater than the liquid velocity, the bubble-formation frequency varies linearly with the difference between the two velocities, but not with their individual values.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Physics of Fluids A (ISSN 0899-8213); 1; 967-974
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  • 6
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    Longitudinal and transverse modes of slosh wave excitation in rotating dewar associated with gravity jitters (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Characteristics of slosh waves based on the dynamical behavior of oscillations at the liquid-vapor interface have been investigated. Twelve case studies of slosh wave excitation due to various frequencies of gravity jitters under different rotating speeds of the propellant tank and different levels of background gravity environment have been simulated. The study shows that slosh waves excited inside the spacecraft propellant tank are characterized by the lowest frequency of the waves initiated, frequencies of the gravity jitters imposed on the propellant system, the levels of background gravity environment, and dewar rotating speeds. Conditions for suppression and amplification of the slosh waves are discussed.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: IAF PAPER 91-404
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  • 7
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    A simple circular-polarized antenna: Circular waveguide horn coated with lossy magnetic material (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A circular waveguide horn coated with a lossy material in its interior wall can be used as an alternative to a corrugated waveguide for radiating a circularly polarized (CP) field. To achieve good CP radiation, the diameter of the structure must be larger than the free-space wavelength, and the coating material must be sufficiently lossy and magnetic. This device is cheaper and lighter in weight than the corrugated one.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA-CR-177092 , NAS 1.26:177092 , UILU-ENG-86-2554 , ELSR-86-8
    Format: application/pdf
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  • 8
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    Gravity-jitters and excitation of slosh waves (1990)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The instability of liquid and gas interface can be induced by the pressure of longitudinal and lateral accelerations, vehicle vibration, and rotational fields of spacecraft in a microgravity environment. Characteristics of slosh waves excited by the restoring force field of gravity jitters have been investigated. Results show that lower frequency gravity jitters excite slosh waves with higher ratio of maximum amplitude to wave length than that of the slosh waves generated by the higher frequency gravity jitters.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 90-0655
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  • 9
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    Fluid stress disturbance activated by gravity jitters induced slosh waves in microgravity (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A full scale Gravity Probe-B (GP-B) Spacecraft propellant dewar tank subjected to various frequencies of gravity jitter have been investigated. Excitation of slosh waves induced by gravity jitter are simulated. Results show that fluid stress distribution exerted on the walls of the rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank. Slosh wave excitations shift the fluid mass distribution in the dewar tank which impose time dependent variations in GP-B Spacecraft moment of inertia, angular momentum, and torque produced by imbalance fluid stresses. This can provide a set of data leading toward the control of spacecraft imbalance caused by the uneven fluid stress distribution from slosh waves.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 92-0880
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  • 10
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    Effect of asymmetric gravity jitter excited slosh waves at liquid-vapor interface under microgravity (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The dynamical behavior of fluids affected by the asymmetric gravity jitter oscillations, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor) in a sub-scale Gravity Probe-B Spacecraft propellant dewar tank imposed by time-dependent various directions of background gravity environment have been investigated. Results show that lower frequency gravity jitter imposed on the time-dependent variations of the direction of background gravity induced a greater amplitude of oscillations and a stronger degree of asymmetry in liquid-vapor interface geometry than that made by the higher frequency gravity jitter. Furthermore, the greater the components of background gravity in radial and circumferential directions will provide a greater contribution in driving more to the increasing amplitude and degrees of symmetry of liquid-vapor interface profiles which, in turn, modify the disturbance of moment of inertia and angular momentum of spacecraft.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: AIAA PAPER 92-0247
    Format: text
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