Direct Measurement of Circulation Using Ultrasound

Hamid Johari, Worcester Polytechnic Institute
William W. Durgin, Worcester Polytechnic Institute

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Article DOI: http://dx.doi.org/ 10.1007/s003480050250

NOTE: At the time of publication, the author William W. Durgin was affiliated with Worcester Polytechnic Institute. Currently, March 2008, he is Provost and Vice President of Academic Affairs at California Polytechnic State University - San Luis Obispo.

Abstract

Ultrasound time-of-flight methods employing counter-propagating ultrasonic pulses are utilized for the direct measurement of circulation in vortical flows. Two schemes are described here which involve either a single straight path or a closed path. Both techniques are shown to result in time differences, between the counter-propagating pulses around the path, linearly proportional to the circulation enclosed by the ultrasound path. The ultrasound methods of circulation measurement do not require calibration constants and can be non-invasive. The reliability of the closed path ultrasound method was assessed by comparing the measured circulation values with those calculated from the lift measurements of a NACA 0012 airfoil. Two examples are also presented where the closed path ultrasound method has been applied to the flow over a delta wing and a free-surface vortex in a cylindrical tank.