Mach Number Control for Continuous Mode Tests in Wind Tunnel Using Feed Forward Algorithm

For a closed-circuit wind tunnel driven by a multiple-stage compressor, continuous mode test can achieve higher efficiency and better data density in comparison of pitch/pause mode test, but fulfilling flow accuracy requirement using the rotation speed of compressor as the only actuator during pitch variation is a challenging task because of the system lag caused by the fluid transport delay. A new method which integrates feed forward and feedback algorithms to accomplish continuous mode test in a 0.6 m × 0.6 m transonic wind tunnel is introduced in this paper. Feed forward parameters is deduced from ‘compressor speed-pitch angle’ curve based on either calculation or empirical data. In the experiments using the new method under the required conditions (Mach number range: 0.6–0.9, speed of pitch angle: 0.2°/s or 0.1°/s, pitch range: −4°–10°), Mach number is well controlled within the error band of ±0.001 in the continuous mode test, and the duration of continuous mode test is much less in comparison of pitch/pause mode test.