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Experimental Studies on 2D Fluid System

KIM, ILDOO (2011) Experimental Studies on 2D Fluid System. Doctoral Dissertation, University of Pittsburgh.

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    Abstract

    A von Kármán vortex street is two rows of counter-rotating vortices which is observed behind an obstacle in a uniform flow. In two-dimensional soap films, laminar vortex streets were generated using obstacles of various shapes. The Strouhal number St=fD/U, where f is the shedding frequency, D is the size of the obstacle and U is the mean flow speed, is measured and compared to a recently proposed St-Re relationship, St=1/(A+B/Re), where the Reynolds number Re=UD/ν, where ν is the kinematic viscosity of the fluid. Our measurements show that in the asymptotic limit (Re→∞), St_{∞}=1/A≈0.21 is constant independent of rod shapes. This suggests that the potential flow is dominant at high Re and that the potential flow around different shaped rods are all strongly affected by the dipolar field. Another coefficient B, which is connected to the thickness of the boundary layer, remains shape-dependent, indicating that for intermediate Re, the St-Re relation is effected by the geometric shape of the rod.An interaction between a soap film and a droplet is also studied. When a micron-sized water droplet impacts on a soap film with speed v_{i}, there exists a critical impact velocity of penetration v_{C}. Droplets with v_{i}<v_{C} merge and flow with the film after impacts, whereas droplets with v_{i}>v_{C} tunnel through it. In all cases, the film remains intact despite the fact that the droplet radius (R_{0}=26μm}) is much greater than the film thickness (0<h≤10μm). The critical velocity v_{C} is measured as a function of h, and interestingly v_{C} approaches a non-zero value v_{C0}≈520 cm/s in the limit h→0. This indicates that in addition to an inertial effect, a deformation or stretching energy of the film is required for penetration.


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    Item Type: University of Pittsburgh ETD
    ETD Committee:
    ETD Committee TypeCommittee MemberEmail
    Committee ChairWu, Xiao-Lunxlwu@pitt.edu
    Committee MemberJasnow, Davidjasnow@pitt.edu
    Committee MemberLevy, Jeremyjlevy@pitt.edu
    Committee MemberGaroff, Stephensg2e@andrew.cmu.edu
    Committee MemberSavinov, Vladimirvladimirsavinov@gmail.com
    Title: Experimental Studies on 2D Fluid System
    Status: Unpublished
    Abstract: A von Kármán vortex street is two rows of counter-rotating vortices which is observed behind an obstacle in a uniform flow. In two-dimensional soap films, laminar vortex streets were generated using obstacles of various shapes. The Strouhal number St=fD/U, where f is the shedding frequency, D is the size of the obstacle and U is the mean flow speed, is measured and compared to a recently proposed St-Re relationship, St=1/(A+B/Re), where the Reynolds number Re=UD/ν, where ν is the kinematic viscosity of the fluid. Our measurements show that in the asymptotic limit (Re→∞), St_{∞}=1/A≈0.21 is constant independent of rod shapes. This suggests that the potential flow is dominant at high Re and that the potential flow around different shaped rods are all strongly affected by the dipolar field. Another coefficient B, which is connected to the thickness of the boundary layer, remains shape-dependent, indicating that for intermediate Re, the St-Re relation is effected by the geometric shape of the rod.An interaction between a soap film and a droplet is also studied. When a micron-sized water droplet impacts on a soap film with speed v_{i}, there exists a critical impact velocity of penetration v_{C}. Droplets with v_{i}<v_{C} merge and flow with the film after impacts, whereas droplets with v_{i}>v_{C} tunnel through it. In all cases, the film remains intact despite the fact that the droplet radius (R_{0}=26μm}) is much greater than the film thickness (0<h≤10μm). The critical velocity v_{C} is measured as a function of h, and interestingly v_{C} approaches a non-zero value v_{C0}≈520 cm/s in the limit h→0. This indicates that in addition to an inertial effect, a deformation or stretching energy of the film is required for penetration.
    Date: 29 June 2011
    Date Type: Completion
    Defense Date: 07 December 2010
    Approval Date: 29 June 2011
    Submission Date: 10 December 2010
    Access Restriction: No restriction; Release the ETD for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    URN: etd-12102010-014259
    Uncontrolled Keywords: fluid; droplet; vortex street; turbulence; soap film; time series
    Schools and Programs: Dietrich School of Arts and Sciences > Physics
    Date Deposited: 10 Nov 2011 15:10
    Last Modified: 25 May 2012 11:22
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-12102010-014259/, etd-12102010-014259

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