Published in 26th AIAA Fluid Dynamics Conference: San Diego, CA, June 19, 1995, pages 1-11. AIAA 95-2269. Reprinted with permission of the American Institute of Aeronautics and Astronautics, Inc. Publisher website: http://www.aiaa.org/content.cfm?pageid=2.
NOTE: At the time of publication, the author William W. Durgin was not yet affiliated with Cal Poly.
An ultrasonic system was developed to measure the circulation about a sinusoidally pitching NACA 4418 airfoil. The system consisted of two opposing ultrasonic ranging modules arranged such that the differences between the sound propagation times in opposite directions could be related to the instantaneous circulation. For the stationary airfoil, the measured lift coefficient was within 5% of the tabulated data while the observed stall angle was 2° less than the tabulated value. Measured hysteresis loops verified the applicability of the ultrasonic system to the dynamic stall problem. Measured maximum lift coefficients increased linearly with reduced frequency up to a value of 0.05. Beyond this value, a slower increase of maximum CL with reduced frequency was observed. Nomenclature coefficients are primarily dependent on the angle of observed.