Continuous Pseudorandom Longitudinal Velocity Perturbations in an Unsteady Low-Speed Wind Tunnel*

Longitudinal velocity perturbations have been studied experimentally using active control methods over the last 75 years. To generate these perturbations in a wind tunnel, a system of counter-rotating louvers can be utilized to vary the blockage ratio and impose fluctuations in the test-section airspeed. Such a system has been implemented in the low-speed wind tunnel at the University of Colorado Boulder which can be commanded to produce pseudorandom, longitudinal velocity perturbations. A pseudorandom louver motion was prescribed such that the test-section air speed would have a predicted energy decay rate proportional to the Kolmogorov energy cascade. Experiments were conducted to investigate the fluid system response to these pseudorandom louver motions. For an input signal with a prescribed energy decay rate proportional to the Kolmogorov energy cascade, the test-section airspeed decayed at the same rate but was attenuated above 7 Hz. Future work will investigate the coupling of these velocity perturbations with passive turbulence generation grids in the test-section.