• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    A numerical investigation of the unsteady flow and heat transfer in a forced and unforced confined laminar impinging

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_td_9957930_sip1_w.pdf
    Size:
    46.26Mb
    Format:
    PDF
    Download
    Author
    Chiriac, Victor Adrian
    Issue Date
    1999
    Keywords
    Engineering, Aerospace.
    Engineering, Mechanical.
    Advisor
    Ortega, Alfonso
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Abstract
    A numerical finite-difference model, derived using a control-volume approach, is used to compute the flow and heat transfer characteristics of a confined laminar air jet impinging on an isothermal surface. Four cases are considered, with Re = 250, 500, 650 and 750, and nozzle-to-plate spacing, H/W = 5. At Re = 250, the boundary layer developing on the target plate separates. At Re = 500, the boundary layer develops without separation off the target wall, the jet momentum is sufficient to overcome the adverse outer field and wall effects. The flow is symmetric at these Reynolds numbers, and maximum values for pressure, friction and heat transfer coefficients occur at the stagnation point. The flow at Re = 650 displays asymmetry as the jet buckles, both flow and heat transfer indicate a transition to an unsteady regime. The critical Reynolds number for the onset of unsteady flow is between 585 and 610. When Re is further increased to 750, the jet "buckles" severely and vortices are shed in the high shear regions. The spectral distribution of the velocity in the jet streamwise and spanwise directions at three distinct locations in the jet, point out three dominant frequencies. The lowest frequency, at 3.66 Hz, is associated with the jet "sweeping" the wall, identified as the "flapping" motion. The highest frequency, 12.96 Hz, is related to the "buckling" motion of the jet at the frequency at which vortices are formed in the jet shear layer. As a result of the two combined unsteady modes, the peak heat transfer is enhanced and the lateral extent of the effective cooling is broadened. A distinct demarcation in time averaged Nusselt number was observed between the steady behavior for Re < 600, and the unsteady behavior for Re > 600. The jet subjected to twenty-four types of forcing reveals two cases relevant in terms of flow and heat transfer control. The out-of-phase forcing at the dominant frequency of 10.68 Hz, Re = 650, stabilizes one side of the confined impinging jet. This results in an enhanced wall heat transfer and peculiar behavior of the hydrodynamic field. When forcing out-of-phase at a dominant frequency of 12.96 Hz, Re = 75 0, the jet is stabilized completely. The forcing suppresses the high-amplitude low-frequency "flapping" jet motion, and the jet tip displacement on the target wall captures only the high-frequency low-amplitude oscillatory motion of the jet. The suppression of the jet "flapping" motion leads to a smaller "patch" heat transfer coefficient. However, since the jet washes the target wall without separation, the wall-averaged heat transfer is much higher than the unforced cases. For the out-of-phase forcing at 12.96 Hz, the "patch" heat transfer is 24% lower than the unforced case, while the wall-averaged heat transfer is 35% higher.
    Type
    text
    Dissertation-Reproduction (electronic)
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Aerospace and Mechanical Engineering
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.