Flow field performance analysis of the multi-fan wind tunnel based on a modular partitioned rotational speed control strategy

To address the critical demand for highly stable flow fields required in the wind field simulation for urban low-altitude operations of small unmanned aerial vehicles, and to systematically solve the inherent problems of insufficient flow field uniformity and weak resistance to environmental crosswind interference typically observed in multi-fan wind tunnel flow fields, multi-fan wind tunnels with 3 × 3 and 4 × 4 array configurations are selected as the primary research objects. Specifically, two novel rotational speed control strategies based on dual-module and three-module partitioning are developed to actively manipulate the flow characteristics. Comprehensive computational fluid dynamics numerical simulations, alongside scaled physical experiments conducted specifically on the 3 × 3 array configuration prototype, were systematically carried out. These methods aim to deeply analyze, thoroughly verify and ultimately optimize the streamwise velocity uniformity as well as the dynamic resistance to crosswind interference within the generated flow fields. The quantitative results demonstrate that in the dual-module rotational speed control strategy, configuring the rotational speed of the outer module to be moderately higher than that of the inner module can effectively compensate for the natural diffusion attenuation occurring in the outer flow field. Consequently, compared with the conventional integral control strategy, under the dual-module rotational speed control strategy, the effective distances required for the flow fields of the 3 × 3 and 4 × 4 array configurations to successfully meet the rigorous coefficient of variation (the ratio of the standard deviation of velocity to the mean velocity) control standard are significantly extended by 200% and 150%, respectively. Furthermore, the three-module rotational speed control strategy can further improve the flow field uniformity specifically at medium and long distances; compared with the dual-module strategy, under the three-module rotational speed control strategy, the average coefficients of variation of the flow field at medium and long distances for the 3 × 3 and 4 × 4 array configurations are reduced by an average of 1.13% and 3.11%, respectively. Finally, increasing the rotational speed of the outer module in both configurations can significantly enhance the resistance to crosswind interference. Compared with the integral control strategy, under 3 m/s crosswind interference, the dual-module rotational speed control strategy reduces the wind velocity deviation ratios in the central regions of the 3 × 3 and 4 × 4 array configurations by an average of 2.08% and 3.62%, respectively.