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On the Manipulation of a Turbulent Boundary Layer by Unsteady Boundary Conditions

Citation

Wang, Cong (2019) On the Manipulation of a Turbulent Boundary Layer by Unsteady Boundary Conditions. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/FT8M-PM75. https://resolver.caltech.edu/CaltechTHESIS:06072019-114300433

Abstract

Reducing the frictional drag generated by a turbulent boundary layer (TBL) is critical for many engineering applications. Motivated by existing turbulent drag reduction methods, this study explores the possibility of sustaining wall-attached air-films and manipulating the near-wall turbulence in hydrodynamic TBL. An innovative air-retaining system is designed to sustain and dynamically modulate the wall-attached air-films in TBL. In still water, the oscillating air-films induce vortical motions in the near-region of air-films. In TBL, phenomena such as Stokes-type oscillatory motion, zero- shear-stress layer, 'inactive' turbulence and reduced viscous shear stress are observed in the vicinity region of air-films. The analysis shows that TBL momentum transfer toward the wall is suppressed and a turbulence re-laminarization mechanism is induced in the near-wall region. One potential physical mechanism points to the process of vorticity generation in the near-region of oscillating air-films, which 'pushes' the TBL near-wall vortical structures away from the wall. With this viewpoint, the phenomena mentioned above can be explained. The modified momentum transfer mechanism and turbulence re-laminarization process are shown to be the potential cause of suppressed viscous shear stress in the near-wall region. Estimated using the Clauser chart method, the turbulent wall-skin friction shows a noticeable decrease in the presence of air-films.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Turbulent boundary layer, flow manipulation, turbulent wall-skin friction reduction
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Awards:Donald Coles Prize in Aeronautics, 2019. The Ernest E. Sechler Memorial Award in Aeronautics, 2018. Standback Fellowship, 2014.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Gharib, Morteza
Group:GALCIT
Thesis Committee:
  • Pullin, Dale Ian (chair)
  • Colonius, Timothy E.
  • Brown, Garry L.
  • Gharib, Morteza
Defense Date:29 May 2019
Non-Caltech Author Email:wangcongxcl (AT) gmail.com
Funders:
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-15-1-2479
Record Number:CaltechTHESIS:06072019-114300433
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:06072019-114300433
DOI:10.7907/FT8M-PM75
ORCID:
AuthorORCID
Wang, Cong0000-0002-8271-5637
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:11710
Collection:CaltechTHESIS
Deposited By: Cong Wang
Deposited On:10 Jun 2019 22:28
Last Modified:12 Dec 2019 21:35

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