Rigid, guyed masts of a proposed type for supporting meteorological instruments would be designed to withstand considerably stronger winds than those conventionally used. The proposed fairings would also help minimize perturbations of airflows and thereby minimize the contaminating effects of the masts on measurements taken by instruments mounted on the masts.
The masts would be constructed in modular sections, each 3.3 m long, that could be connected together to achieve the desired overall height. Typically, three sections would be used (see figure) to obtain the standard wind-sensor height of 10 m as specified by the World Meteorological Organization. The base of the mast would be mounted rigidly in the ground.
The main structural member in each section of a mast would be a cylindrical tube. The fairing would be a vertically finned, neutral-lift airfoil that would surround the tube. The airfoil would be free to pivot azimuthally around the tube to align itself with the wind as directed by the vertical fin section. The airfoil would pivot on bearings mounted on circular flanges at the ends of the tube. The circular flanges above each section would provide attachment points for guy wires. The flanges at the lower end of the sections could serve as bearing surfaces.
To minimize aerodynamic drag caused by vertical winds acting on the circular flanges, the size and shape of the flanges should be kept to a minimum but consistent with the need to provide clearance between the guy wires and the airfoils. The airfoil ends should be trimmed to eliminate mechanical interference with the flanges or guy wires. If there is a need for further reduction of the wind load on the entire structure, then the guy wires could also be faired with airfoils in a manner similar to that of the sections of the mast.
When a cylinder is faired with a neutral-lift airfoil which is free to pivot with the wind, the effect is equivalent to dividing the drag coefficient, diameter, or length of the cylinder by approximately a factor of 8. Conversely, it could be viewed as reducing the equivalent speed of the wind acting on the cylinder to 8 -½(≈1/2.8) of its actual value. This approach can result in substantial improvements of non-aerodynamically-faired conventional towers and masts, which can typically withstand winds of no more than about 125 mi/h (56 m/s). Simply by changing the structural members to self-aligning, neutral-lift airfoils, wind loads would be reduced enough to enable the structures to withstand winds up to 350 mi/h (156 m/s).
This work was done by Jan A. Zysko of Kennedy Space Center. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Mechanics category, or circle no. 141 on the TSP Order Card in this issue to receive a copy by mail ($5 charge).
Inquiries concerning rights for the commercial use of this invention should be addressed to
the Patent Counsel
Kennedy Space Center; (407) 867-6225.
Refer to KSC-11741.