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    On the Impact of Spheres onto Liquid Pools and Ultra-viscous Films

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    Name:
    PhD_Thesis_final_-_Mohammad_Mujtaba_Mansoor.pdf
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    7.916Mb
    Format:
    PDF
    Description:
    Mansoor Final Dissertation
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    Type
    Dissertation
    Authors
    Mansoor, Mohammad M. cc
    Advisors
    Thoroddsen, Sigurdur T cc
    Committee members
    Farooq, Aamir cc
    Sun, Shuyu cc
    Sigurdson, Lorenz
    Program
    Mechanical Engineering
    KAUST Department
    Physical Science and Engineering (PSE) Division
    Date
    2016-06
    Embargo End Date
    2017-07-10
    Permanent link to this record
    http://hdl.handle.net/10754/615877
    
    Metadata
    Show full item record
    Access Restrictions
    At the time of archiving, the student author of this dissertation opted to temporarily restrict access to it. The full text of this dissertation became available to the public after the expiration of the embargo on 2017-07-10.
    Abstract
    The free-surface impact of spheres is important to several applications in the military, industry and sports such as the water-entry of torpedoes, dip-coating procedures and slamming of boats. This two-part thesis attempts to explore this field by investigating cavity formation during the impact of spheres with deep liquid pools and cavitation in thin ultra-viscous films. Part I reports results from an experimental study on the formation of stable- streamlined and helical cavity wakes following the free-surface impact of heated Leidenfrost spheres. The Leidenfrost effect encapsulates the sphere by a vapor layer to prevent any physical contact with the surrounding liquid. This phenomenon is essential for the pacification of acoustic rippling along the cavity interface to result in a stable-streamlined cavity wake. Such a streamlined configuration experiences drag coefficients an order of magnitude lower than those acting on room temperature spheres. A striking observation is the formation of helical cavities which occur for impact Reynolds numbers Re0 ≳ 1.4 × 105 and are characterized by multiple interfacial ridges, stemming from and rotating synchronously about an evident contact line around the sphere equator. This helical configuration has 40-55% smaller overall force coefficients than those obtained in the formation of stable cavity wakes. Part II of this thesis investigates the inception of cavitation and resulting structures when a sphere collides with a solid surface covered with a layer of non-Newtonian liquid having kinematic viscosities of up to v0 = 20,000,000 cSt. The existence of shear-stress- induced cavitation during sphere approach towards the base wall (i.e. the pressurization stage) in ultra-viscous films is shown using a synchronized dual-view high-speed imaging system. In addition, cavitation by depressurization is noted for a new class of non-contact cases whereby the sphere rebounds without any prior contact with the solid wall. Horizontal shear rates calculated using particle image velocimtery (PIV) measurements reveal the apparent fluid viscosity to vary substantially as the sphere approaches and rebounds away from the base wall. A theoretical model based on the lubrication assumption is also solved for the squeeze flow in the regime identified for shear-induced cavity events to investigate the criterion for cavity inception in further detail.
    Citation
    Mansoor, M. M. (2016). On the Impact of Spheres onto Liquid Pools and Ultra-viscous Films. KAUST Research Repository. https://doi.org/10.25781/KAUST-B4EN1
    DOI
    10.25781/KAUST-B4EN1
    ae974a485f413a2113503eed53cd6c53
    10.25781/KAUST-B4EN1
    Scopus Count
    Collections
    PhD Dissertations; Physical Science and Engineering (PSE) Division; Mechanical Engineering Program

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