Impact of Active Turbulence Generation System in 3/4 Open-Jet Wind Tunnel: Flow Structures, Shear Layer, and Low-Frequency Fluctuations

With increasing attention to complex aerodynamic conditions such as crosswinds, gusts, road turbulence, and vehicle queuing, accurately reconstructing these unsteady and turbulent environments in automotive wind tunnels has become a significant challenge. Addressing this challenge is crucial for broadening experimental conditions and advancing research in unsteady aerodynamics. However, the integration of turbulence generation systems impacts low-frequency fluctuation phenomena, leading to pressure and velocity inaccuracy, and also affects the flow structure in the test section as well, especially in the jet shear layer. In this paper, the impact of an active turbulence generation system on turbulence characteristics and flow structures within jet shear layer in a wind tunnel is numerically investigated. By comparing the flow structure among the blank wind tunnel, and wind tunnel with static and dynamic active turbulence generation system, the mechanisms underlying these configurations are analyzed. In addition, low-frequency fluctuations with the presence of active turbulence generation system are compared to those observed in the blank wind tunnel. The results indicate that while the turbulence generation system effectively produces the desired turbulent components, it also increases the non-uniformity of the jet shear layer, and hence intensifies low-frequency fluctuations in the test section.