A well-known problem with open-jet wind tunnels are low-frequency pulsations, which affect the flow quality and thus the quality of the measured data. This so-called wind tunnel buffeting is caused by large-scale vortices in the shear layer, which excite acoustic resonant modes of the wind tunnel circuit.
This paper presents a novel approach to control low-frequency pulsations by means of active flow control at the nozzle exit. The final setup consists of oscillated flaps which are actuated by electrodynamic shakers. Single-frequency sinusoidal signals and band-limited random signals were used for excitation. The oscillated flaps prevent the synchronization of vortex shedding with acoustic resonance by generating forced perturbations in the shear layer at a frequency that is different from the acoustic resonance.
The flaps - which were named FKFS-flaps by the authors - were installed at the IVK 1:4 model-scale wind tunnel. Experimental results from an ongoing experimental study are presented showing the reduction of low-frequency pulsations and the influence of the flaps on pressure distribution and force measurements.
The small space requirements of the FKFS-flaps allows retrofit of existing wind tunnels without major modifications to the tunnel. The installation cost is considerably lower than that of other active systems. Very simple open-loop control is used, which is easier to implement and more stable than a closed-loop system.