Spectral feedback control of turbulent spectra in a wind tunnel

Longitudinal flow velocity control was conducted in the Andrew Fejer Unsteady Wind Tunnel to produce velocity spectra that emulate atmospheric turbulence. A louver mechanism placed at the downstream end of the test section determines the resistance to the flow by varying the louver deflection angle, and hence changes the test-section velocity. The test-section flow velocity was decomposed into an adjustable mean flow u(0) and a fluctuation u', which were respectively controlled by the mean louver deflection angle and the oscillations of the louvers about that mean angle. A linear interpolation of the static map of the test-section flow speed with respect to the louver deflection angle was used as an open-loop controller for the longitudinal flow velocity. A feedback loop that measures the velocity spectrum over a short time interval constructed a closed-loop controller, which controls the mean flow speed as well as the amplitudes over a range of individual frequencies within the fluctuation spectrum. The spectral feedback approach was tested by generating the longitudinal velocity components of von Karman turbulence spectra and Dryden turbulence spectra. The controller proved to be capable of controlling the gust frequency with a bandwidth of 7 Hz given the current hardware configuration.