Experimental study of the effect of helical grooves on an infinite cylinder

Abstract

A series of low-speed wind-tunnel investigation were conducted to determine the aerodynamic behavior of a grooved cylinder representing a long trailing wire antenna towed from an orbiting airplane. The large angle-of-attack range of the trailing wire required two different model configurations. The first configuration, using full-scale wire lengths suspended between steel stanchions, was mounted on a flush four-degree-of-freedom wall balance. The second configuration, used a 15-scale grooved cylinder model with an ogive nose mounted on a six-degree-of-freedom sting balance. Wall balance wire data, valid for higher angles of attack, were integrated with low angle-of-attack sting balance data. Empirical relationships for the normal and axial force coefficients were verified with historical references for tested clean circular cylinders and extended for the grooved configurations. Existence of a side force coefficient due to circulation caused by the helical grooves was discovered, expressed analytically, and verified with flow-visualization techniques. Finally, the experimental coefficients were used to improve an existing simulation model describing the static equilibrium conditions of a cable towed.by an airplane in a circular orbit. Inclusion of the side force influence in the static model proved consistent with the lateral skew angle and direction observed during flight test.