Boundary Layer Disturbances Caused by Periodic Heating of a Thin Ribbon.
AIR FORCE INST OF TECH WRIGHT-PATTERSON AFB OH SCHOOL OF ENGINEERING
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Wind tunnel tests were conducted to generate velocity perturbations in a laminar boundary layer using periodic heating of a flush-mounted ribbon. A thin strip of Nichrome ribbon, flush-mounted on a flat plate, was heated by pulsed voltage of various frequencies with spring tension and used to take up the slack caused by thermal expansion. Vibration of the ribbon was excited by the periodic thermal expansion and contraction due to the pulsed voltage. Sinusiodal velocity fluctuations were detected by a hot wire anemometer when the ribbon was allowed to vibrate during pulsed heating. No effect on the amplitude of the flow disturbances was detected with the spring tension removed and segments of the ribbon firmly fixed to the surface such that no vibration of the ribbon occurred during periodic heating. Pulsed heating of a thin ribbon caused detectable flow disturbances only when the ribbon was allowed to vibrate. The AFIT 9-in wind tunnel had sufficiently low turbulence to detect fluctuations when pulsed voltage was applied to the ribbon. Experiments conducted in AFITs 14-in wind tunnel were not able to show effects of heating because of the large amount of free-stream turbulence. Theses
- Fluid Mechanics