Evaluation of an Unsteady Yaw, Gust, and Broadband Turbulence Generation System for Closed-Loop Automotive Wind Tunnels

<div>This study investigates the flow characteristics in the test section of a model-scale, three-quarters open-jet, closed-loop return wind tunnel equipped with a novel device featuring three subsystems to generate transient yaw, gusts, and turbulence. The effect of each subsystem on the resulting turbulent and unsteady flows is evaluated individually and simultaneously. It is demonstrated that this new turbulence generation system can generate yaw distributions with standard deviations ranging from 2.1° to 8.0°. This replicates a wide range of on-road yaw behavior. Additionally, the subsystems can activate transient yaw events and unsteady gusts. Frequency sweeping was demonstrated to fill a wide range of low-frequency spectra, which helps recreate the on-road flow spectra in wind tunnels. Unsteady gusts of more than 15% of the mean flow velocity were achieved. The active turbulence subsystem generates turbulence levels from a few percent, passively, to over 20% intensity levels actively, with tailorable levels depending on input parameters to the active grid. Combined, the subsystems were demonstrated to achieve a wide range of yaw distributions with different standard deviations and features of the on-road turbulence spectrum, from low-frequency events to broadband turbulence with significant inertial subrange within the model-scale wind tunnel.</div>