Influencing rule of accelerating flow's key parameters on unsteady aerodynamic forces of a 3:2 rectangular prism

Direct measurements of aerodynamic forces on a segmental model of a rectangular section with 3:2 side ratio were conducted for varying accelerating flows. The findings indicate that the unsteady characteristic of lift force is more pronounced than that of drag force, particularly at the wind attack angle of 10 degrees. Both the time-varying mean and dynamic components of the lift force exhibit unsteadiness at this angle. A novel approach employing the discrete wavelet packet transform is then proposed to decompose the time-varying mean and dynamic components of the lift force. Subsequently, the influencing rule of accelerating flow's key parameters on these force components is discussed and validated through comparison with the experimental data. The results highlight that the key parameters of accelerating flow governing the unsteady characteristics of lift force are starting wind velocity, average acceleration, and acceleration rising time. For the time-varying mean of lift force, the maximum inertial force is observed to increase linearly with average acceleration. Decreasing starting wind velocity and reducing acceleration rising time accentuate the magnitude of the time lag. Regarding the dynamic component of lift force, a shorter acceleration rising time and lower starting wind velocity amplify its amplitude. Additionally, the frequency of lift force is found to be lower than that predicted by the quasi-steady theory, with a reduction in acceleration rising time and starting wind velocity resulting in a further decrease in the frequency of lift force.