Direct measurement of delta wing vortex circulation using ultrasound

The circulation around a closed path encompassing the primary vortex of stationary delta wings is investigated through the use of ultrasound. Ultrasonic pulses were propagated clockwise and counterclockwise along a fixed, closed path which was positioned perpendicular to the delta wing root chord lines. Circulation in the plane of the closed path was then determined from the transit time difference between the clockwise and counterclockwise pulses. Half-delta wings of 60- and 70-deg sweep angle were tested over a range of angles of attack from 2 to 38 deg and from 2 to 52 deg, respectively, in 20 increments, and at distances of 35, 50, 65, and 80 percent root chord from the wing apexes. Circulation behavior was examined as it relates to these parameters and to primary vortex burst location. Circulation was measured to grow nonlinearly with angles of attack for which the burst point remained downstream of the wing planform; circulation then increased in an approximately linear manner with increasing angle of attack until the burst point reached the vicinity of the wing apex. Circulation was found also to increase approximately linearly with increasing chordwise location at constant angles of attack. (Author)