Numerical Study On Performance Of Bionomic Fin-like Wing

In the process of natural selection,fish evolved a series of physiological structures to hunt prey and avoid hunting.For example,most fish have fins.Fins often play a decisive role in the propulsion of fish motion.The study on fin motion and its flow control mechanism is not only of scientific significance but also provides a valuable idea for the design of underwater bionic vehicle.Most fins of fish are not smooth,the radial fin ray which connected by the collagen membrane forms a groove structure.However,there are only a few works about the influence of the groove structure on the flow field and flow performance.In this paper,the mechanical properties and flow control mechanism of fin-like wings are studied by comparing with ordinary wings.The flow characteristics and mechanical properties of finlike wings in pitching and heaving motion,its decomposition movement and C-start motion are numerically studied by solving the N-S equation of unsteady incompressible flow.We also analyzed the influence of the motion parameters and geometric parameters.In this paper,the results show that the drag force of the fin-like wing is larger than the ordinary wing when static,but in pitching and heaving motion and C-start motion,the fin-like wing achieves better mechanical performance than that of ordinary wing.In the pitching and heaving motion,the fin-like wing produces not only the span-wise vortices,but also the normal and flow direction vortices.These vortices significantly affect the pressure distribution and the backward jet in the wake.So the fin-like wing can gain higher thrust and propulsion efficiency than that of ordinary wing.In pitching motion,the fin-like wing produces the leading-edge vortices,and the propulsion advantages are more obvious.In heaving motion,the propulsion performance of fin-like wing is worse than the ordinary wing.When the flapping frequency increases,the fin-like wing achieves more advantages over ordinary wing,and gets better propulsion performance in higher frequency flapping.The fin-like wings with different groove sizes all show better propulsion performance than that of ordinary wing in pitching and heaving motion.Among these fin-like wings with different groove sizes,the one designed on the real measured data has the highest propulsion efficiency.In the C-start,the propulsion performance of fin-like wing is better than that of ordinary wing,and the lateral force is also greatly improved.Due to the inducement of vortices,the thrust and lateral force of the fin-like wing are significantly higher than those of the ordinary wing in the propulsion stage.However,the preparation stage and the stay stage are necessary for the formation of the vortices in the later propulsion stage.When the stay stage is shortened to half,the fin-like wing gets more advantages than the ordinary wing,while when the stay stage is removed,the fin-like wing loses its advantages.In the range of parameters selected in this paper,the fin-like wing produces greater the thrust and lateral force produced with the wider groove in C-start.