Frequency characteristics of axisymmetric conical boattail models with different slant angles

This study focuses on the unsteady behavior of the flow around axisymmetric conical boattail models under low-speed conditions. Particle image velocimetry was conducted on the symmetric plane for four boattail models with angles of 0°, 10°, 16°, and 22°. Different data processing techniques, including variational mode decomposition (VMD), fast Fourier transform, proper orthogonal decomposition (POD), and multiscale proper orthogonal decomposition (mPOD), were applied to understand the effects of boattail angles on the characteristic frequency of the wake flow. Our results indicated that vortex shedding, bubble pumping, and the rotation of vortex shedding are the three dominant modes for four boattail configurations. However, the energy of vortex shedding mode becomes comparable to that of bubble pumping for the model with the boattail angle of 22°. The orientation of the shear layer remarkably changes near the boattail surfaces for different angles, which is connected to the flow behavior on the surface. This study also suggests that VMD and mPOD are advantageous data-driven methods for analyzing turbulent flows. © 2023 Author(s).