Fish-like swimming in oblique flows: A numerical investigation

Abstract

Although being a common situation for fish and underwater vehicles, limited research has been reported for a fish-like body swimming in oblique incoming flows. The present work employs the immersed boundary-lattice Boltzmann method to numerically study the dynamics of this problem. A more comprehensive analysis method, which utilizes the effective force parameters that consolidate the angle of attack (AOA) into the traditional force parameters, is proposed for investigating the dynamics of cases with non-zero AOA. Several distinct features in terms of the dynamic performance, the periodic features, and the flow field characteristics are presented. For the dynamic performance, undulation amplitude plays a more dominant role than the undulation form in thrust generation. The periodic features revealed by the Fourier spectra present increasing complexity with larger AOA. Besides, three flow regimes are identified, one of which observes hierarchical vortex structures with different orders in time and space. The small-scale vortex street generated by undulation is “local” in both time and space, and it is embedded in the large scale vortex street generated by the body and the free-stream.