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

Handle URI:
http://hdl.handle.net/10754/615877
Title:
On the Impact of Spheres onto Liquid Pools and Ultra-viscous Films
Authors:
Mansoor, Mohammad Mujtaba ( 0000-0001-9196-0960 )
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.
Advisors:
Thoroddsen, Sigurdur T ( 0000-0001-6997-4311 )
Committee Member:
Farooq, Aamir ( 0000-0001-5296-2197 ) ; Sun, Shuyu ( 0000-0002-3078-864X ) ; Sigurdson, Lorenz
KAUST Department:
Physical Sciences and Engineering (PSE) Division
Program:
Mechanical Engineering
Issue Date:
Jun-2016
Type:
Dissertation
Appears in Collections:
Dissertations

Full metadata record

DC FieldValue Language
dc.contributor.advisorThoroddsen, Sigurdur Ten
dc.contributor.authorMansoor, Mohammad Mujtabaen
dc.date.accessioned2016-07-10T11:47:50Z-
dc.date.available2016-07-10T11:47:50Z-
dc.date.issued2016-06-
dc.identifier.urihttp://hdl.handle.net/10754/615877-
dc.description.abstractThe 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.en
dc.language.isoenen
dc.subjectImpacten
dc.subjectCavitationen
dc.subjectLeidenfrosten
dc.titleOn the Impact of Spheres onto Liquid Pools and Ultra-viscous Filmsen
dc.typeDissertationen
dc.contributor.departmentPhysical Sciences and Engineering (PSE) Divisionen
thesis.degree.grantorKing Abdullah University of Science and Technologyen_GB
dc.contributor.committeememberFarooq, Aamiren
dc.contributor.committeememberSun, Shuyuen
dc.contributor.committeememberSigurdson, Lorenzen
thesis.degree.disciplineMechanical Engineeringen
thesis.degree.nameDoctor of Philosophyen
dc.person.id118496en
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