A Two-degree-of-Freedom Oscillator for Unsteady Aerodynamics Applications

摘要

Numerous wind tunnel studies of airfoil dynamic stall have been limited to harmonic model oscillations, but new microcomputers and hybrid servo systems have now been exploited to produce a mechanism which provides a high degree of flexibility in achieving arbitrary model motions in multiple degrees of freedom over a wide range of motion alternatives. A prototype apparatus has been fabricated to provide simultaneous motions of an airfoil or wing model in both pitch and translation. Drive motors provide independent motion in two axes under the control of servo-translator units which respond to pulse trains generated by the microcomputer, using analog position and feedback loops to smooth the pulses. Programs are developed in a higher-level language using a larger disk-based computer system and then the program task image is downline-loaded through a network communications link to the smaller computer. In addition to a thorough description of the experimental apparatus, the various elements of motion control, including servo-translator dynamic characteristics, software techniques for pulse train generation, and required computer interface circuitry are discussed. Measurements of constant rate, constant acceleration, and pure harmonic motions are examined for both drive axes over the entire range of drive parameters. (Author)