Spherical Balloon Wind Sensor Behavior

James R. Scoggins NASA-Marshall Space Flight Center, Huntsville, Ala.

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Abstract

Response characteristics of freely rising superpressured spheres of different configurations are discussed. Wind profile data measured by the superpressured balloon method, the smoke trail method, the AN/GMD-1 rawinsonde system, and from low-level oper-air tests were used in the analysis. Results are reported on data measured at Huntsviile, Alabama, at night during stable conditions to an altitude of 120 m and at Cape Kennedy to an attitude of 12 km. The results show that: (1) the average drag curve for a freely rising 2-m diameter, smooth superpressured sphere differs considerably from the drag curve obtained in wind tunnels using smaller spheres; the average value of the drag coefficient is larger over all Reynolds numbers except near the transition region; (2) the drag coefficient for roughened spheres is nearly independent of the Reynolds number but decreases slightly as the Reynolds number decreases; (3) the addition of surface roughness elements reduces the aerodynamically induced horizontal motions of the smooth sphere; and (4) the average aerodynamic lift force, which acts primarily in the horizontal direction and is responsible for the aerodynamically induced horizontal motions, is negligible indicating that it does not act in any preferred direction.

Abstract

Response characteristics of freely rising superpressured spheres of different configurations are discussed. Wind profile data measured by the superpressured balloon method, the smoke trail method, the AN/GMD-1 rawinsonde system, and from low-level oper-air tests were used in the analysis. Results are reported on data measured at Huntsviile, Alabama, at night during stable conditions to an altitude of 120 m and at Cape Kennedy to an attitude of 12 km. The results show that: (1) the average drag curve for a freely rising 2-m diameter, smooth superpressured sphere differs considerably from the drag curve obtained in wind tunnels using smaller spheres; the average value of the drag coefficient is larger over all Reynolds numbers except near the transition region; (2) the drag coefficient for roughened spheres is nearly independent of the Reynolds number but decreases slightly as the Reynolds number decreases; (3) the addition of surface roughness elements reduces the aerodynamically induced horizontal motions of the smooth sphere; and (4) the average aerodynamic lift force, which acts primarily in the horizontal direction and is responsible for the aerodynamically induced horizontal motions, is negligible indicating that it does not act in any preferred direction.

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