Modeling and Computation of Batoid Swimming Inspired Pitching Impact on Wake Structure and Hydrodynamic Performance

Abstract

Abstract Through direction numerical simulation (DNS) of a model manta ray body, pectoral fin scaled pitching effect on hydrodynamic performance and wake is investigated. The manta ray model is derived from high-speed video of manta ray swimming with motion of the model prescribed to match the actual manta ray. Rotation angles of the model skeletal joints is altered to scale the pitching. This results in four manta ray models with different pectoral fin pitching ratios. The models are simulated using an in-house developed immersed boundary method-based numerical solver. Notable discrepancies in thrust production during the downstroke are observed, with the θR = 1.0 case producing instantaneous thrust peak that is 19% higher than the θR = 0.72 model. Cycle averaged thrust is highest for the θR = 0.72 model case, however, which can be attributed to extended reverse thrust for the θR = 1.0 model. Through analysis of the near-body wake structures produced during the downstroke, late leading-edge vortex (LEV) formation is discovered to be primarily responsible for the detrimental reverse thrust seen for the θR = 1.0 model. Surface pressure contours confirm this finding. Meanwhile the upstroke possesses less pronounced force production.