Kenny Chung-Siu Kwok

Wind tunnel testing has undergone a significant transformation. Traditionally, it focused on generating uniform, low-turbulence flows for clean aerodynamic testing of aircraft models. Early advancements broadened this scope to include homogeneous and isotropic turbulence, as well as atmospheric boundary layers, which are crucial for civil engineering applications. However, modern demands, ranging from civil engineering to the low-altitude economy (e.g., drones), now require the ability to reproduce complex, spatiotemporally rich turbulence. This need has driven the emergence of novel approaches that enable more precise, adaptable, and programable flow generation. The review is structured to examine advances in active turbulence generation methods, multi-fan driving modes, control system architectures, and the emerging role of artificial intelligence in flow modulation. As a representative realization, we present a detailed case study of the Harbin Institute of Technology-Shenzhen (HIT-Sz), multi fan wind tunnel (MFWT), a high-resolution 768-fan array system capable of hybrid modulation, gust replication, and real-time feedback-driven control. These advancements position MFWTs as critical experimental platforms for next-generation aerodynamic testing, marking a significant shift toward robust and adaptable simulation of realistic atmospheric conditions for unmanned aerial vehicles (UAVs) and civil structures operating in complex, turbulent environments.

The scope of the ERIES-SSTURBO project is reviewed in this work, emphasizing the importance of gaining a deeper understanding of the effects that turbulence in general, and turbulent length scale in particular, have in the flow-induced response of bluff bodies. The planned experimental campaign at the Giovanni Solari Wind Tunnel of the University of Genoa is described, testing a 3:2 rectangular prism in smooth flow, as a reference flow-induced response assessment. The effects of large-scale turbulence will be studied based on grid-induced turbulence, while those of small-scale turbulence will be analyzed using rod-induced turbulence, as proposed by Gartshore in 1973. Details are provided about the experimental facility and the instrumentation. Aiming at highlighting the complementarity between the wind tunnel data and high-fidelity 3D LES simulations in the study of turbulent flow effects on the response of bluff bodies, computational results obtained in the frame of an independent project are briefly introduced. It is expected that the results of this experimental campaign will shed light on our understanding of the role played by the turbulent length scale in the interaction between the flow and flexible structures prone to suffer flow-induced excitation. Furthermore, this experimental dataset will be instrumental for the detailed validation of CFD simulations addressing this highly complex problem, allowing to assess the accuracy of computational results.

This study uses two wind tunnel testing approaches: a sole high-frequency pressure scanning (HPS) approach, and a synchronized particle image velocimetry (PIV) and multipoint pressure scanning (SPMPS) approach, to investigate aerodynamic characteristics of a rectangular cylinder. HPS and SPMPS share identical experimental settings and device arrangements, while the SPMPS sampling frequency is much lower than HPS because the PIV system has a low sampling frequency in this study. SPMPS can simultaneously capture the flow field and surface pressure information. PIV measurement provides instantaneous flow field information, helping to analyze flow characteristics, and surface pressure taps offer both high- and low-frequency surface pressure information. It was found that for the rectangular cylinder, the zones of high turbulent kinetic energy and turbulent shear stress are associated with the lower negative pressure coefficient. In addition, diverse coherent structures in the instantaneous flow field resemble different critical points such as the saddle point, the repelling focus, and the attracting focus, and these coherent structures are associated with drastic changes in the pressure distribution or extreme pressure values. In particular, there is a visible flow reattachment, and the lift coefficient is more sensitive to the pressure distribution around the trailing edge of the rectangular cylinder. The convective velocity of wall pressure fluctuations is calculated based on the spatial temporal correlation of HPS information, and the convective velocity on the upper surface of the cylinder of SR = 3.25 is around 3.1 m/s providing evidence that Taylor's hypothesis breaks down for wall pressure fluctuations.