Stability and Drag Reduction in a Boundary Layer with Microbubbles.

Abstract

When microbubbles are injected in a turbulent boundary layer, they promote a reduction of the local skin friction and a sharp mean velocity gradient between the two microbubble free regions in the boundary layer, i.e., the outer edge and the near wall region. In connection with the apparent stability of the bubbles in the boundary layer, the stability of a hollow vortex sheet in an infinite expanse of fluid as well as in the presence of a wall are studied. We concluded that the simple hollow vortex sheet is unconditionally unstable while a stability range was found for a hollow vortex sheet perturbed in the presence of a wall. In all cases, however, the computations suggest that the hollow vortex radius is invariably a destabilizing factor. Regarding the second aspect of the problem, a heuristic, but physically sound explanation of the mechanisms of the drag reduction is proposed. Based on these ideas and using a phenomenological approach, the flat plate boundary layer is numerically analyzed.

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Document Details

Document Type
Technical Report
Publication Date
Feb 01, 1988
Accession Number
ADA191975

Entities

People

  • Joao M. Neves

Organizations

  • Pennsylvania State University

Tags

Communities of Interest

  • Air Platforms
  • Energy and Power Technologies

DTIC Thesaurus Topics

  • Boundary Layer
  • Buoyancy
  • Computational Fluid Dynamics
  • Computational Science
  • Drag
  • Drag Reduction
  • Equations
  • Fluid Dynamics
  • Fluid Mechanics
  • Hydrodynamics
  • Mechanical Properties
  • Skin Friction
  • Stratified Fluids
  • Turbulent Boundary Layer
  • Turbulent Flow
  • Turbulent Mixing
  • Two Dimensional

Fields of Study

  • Physics

Readers

  • Fluid Mechanics and Fluid Dynamics.