23 June 2006 Vortex shedding from a 12-m antenna
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Abstract
Periodic vortex shedding from a 12-m parabola antenna has been found in the wind of 9 m s-1 and an attack angle of 26 degrees. The measurements have been made at the NRAO VLA site. The periodic yaw motion of an elevation axis has been detected with linear gauges mounted on a reference structure that was built in each side of the yoke. It has also been observed in the angle difference of two encoders installed at both ends of the elevation axis. The frequency of yaw motion was 0.15 Hz. The same periodicities have been found in both the wind direction and wind velocity measured with an ultrasonic anemometer in the wake downstream of the antenna. Such periodicities have been seen in neither common displacement of the bearing housings nor rotation of the elevation axis. The Reynolds number of the flow was 6 x 106 (hypercritical), suggesting the vortex shedding be periodic, which is consistent with our observations. The Strouhal number of parabola has been found to be 0.19 that is comparable to those of cylinder, inverse triangle, and other similar geometric shapes. The coefficient for oscillatory lateral force exerted on the antenna by shedding vortices has been estimated to be about 1.
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Nobuharu Ukita, Nobuharu Ukita, Masao Saito, Masao Saito, Bungo Ikenoue, Bungo Ikenoue, Jeffrey G. Mangum, Jeffrey G. Mangum, Nicholas J. Emerson, Nicholas J. Emerson, Angel C. Otarola, Angel C. Otarola, Stefano Stangellini, Stefano Stangellini, } "Vortex shedding from a 12-m antenna", Proc. SPIE 6267, Ground-based and Airborne Telescopes, 62673P (23 June 2006); doi: 10.1117/12.670755; https://doi.org/10.1117/12.670755
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