VISUALIZATION OF QUASI-PERIODIC FLOWS

A self-synchronizing Schlieren flow visualization technique has been developed to study unsteady periodic flows that may result from aeroelastic effects. The technique allows the experimentalist to stroboscopically “freeze” the streak line pattern at any phase in one period of the motion by driving the Schlieren light source with an electronically processed synchronizing signal that is derived by measuring a periodic flow variable with a convenient sensor. Results for the visualization of the near wake behind an oscillating airfoil at low speeds, which show an ordered series of discrete vortices and a curious short-wavelength wake disturbance are examined. Results are also presented for edge tone sound generation. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.