Effect of Flow Oscillations on Cavity Drag and a Technique for Their Control.
Abstract
Experiments to relate the state of the shear layer to cavity drag have been performed in a water channel using 4-in. axisymmetric cavity model. Detailed flow measurements in various cavity flow oscillation phases, amplitude amplification along the flow direction, distribution of shear stress, and other momentum flux obtained by laser Doppler velocimeter are presented. Measurements show exponential dependence of cavity drag on the length of the cavity. A jump in the cavity drag coefficient is observed as the cavity flow shows a bluff body wake type behavior. Natural and forced oscillations are introduced by a sinusoidally heated thin-film strip which excites the Tollmein-Schlichting waves in the boundary layer upstream of lthe gap. For a large gap, self-sustained periodic oscillations are observed, while for smaller gaps, which do not oscillate naturally, periodic oscillations can be obtained by external forcing through the strip heater. The drag of the cavity can be increased by one order of magnitude in the non-oscillating case through external forcing. Also, itis possible to completely eliminate mode switching by esternal forcing. For the first time, it is demonstrated that amplitude of cavity flow Kelvin-Helmholtz wave is dampened or cancelled by introduction of external perturbation of natural flow frequency but different phase. Keywords: Aerodynamics; Cavity flows, Active fluid control.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 30, 1985
- Accession Number
- ADA165732
Entities
People
- A. Roshko
- M. Gharib
- V. Sarohia
Organizations
- Jet Propulsion Laboratory