Research On Hydrodynamic Performance Of The Bionic Oscillating Foil In Vortex Flow Field

In natural water, a variety of creature moving and barrier results in the existance of amass of vortex. In this kind of complex vortex flow field, the fish can still keep goodpropulsion performance with high maneuverability, high efficiency, low noise. The researchon hydrodynamic performance of fish swimming can contribute to development and designof new bionic thruster and it has great significance on the national defense military,environmental protection and economic development.Based on fish swimming propulsion of carangiform combined with crescent caudal fin,the two-dimension oscillating foil is used as the research model, and CFD method is usedfor numerical calculation of the oscillating foil hydrodynamic performance in the karmanvortex street flow field and reverse karman vortex street flow field. This thesis reveals theinteraction between the vortex in flow field and the oscillating foil trailing vortex.Through the numerical simulation of the oscillating foil moving in the steady flow field,this dissertation studies the relationship between control parameters and the oscillating foilhydrodynamic performance. Result shows that the oscillating foil movement processes vortexin the leading edge. The vortex can be thrown in the wake flow field to form the reversekarman vortex street, and it is advantageous to the oscillating foil for obtaining higher thrustforce. St. number is an important parameter which is supposed to reflect the propulsionperformance of the oscillating foil. Within the scope of the parameters studied in the thesis,when the St. number is0.25~0.25, pitching amplitudeθ0is30°~35°, and the phase between the heave and pitch movement is around90°, the oscillating foil can obtain goodpropulsion performance. In this thesis, the highest propulsive efficiency of the oscillating foilcan reach0.65in steady flow field.As for the research on the hydrodynamic performance of the oscillating foil in the vortexflow fields, this thesis mainly studies the effect that the karman vortex street and reversekarman vortex street have on the propulsion performance of the oscillating foil in the flowfield. Results show that compared to the reverse karman vortex street in the flow field, thekarman vortex street is more favorable for the improvement of the oscillating foil propulsionperformance. It is concluded that the highest efficiency of oscillating foil can reach92.5%andthrust coefficient can reach up to2.2times under the influence of karman vortex street. Under the influence of reverse karman vortex street, the maximum propulsive efficiency ofoscillating foil is52.8%and the maximum thrust coefficient can increase by50%.In the vortex street flow field, there are three kinds of interaction modes between thevortex in flow field and the oscillating foil trailing vortex: constructive interaction mode,vortex pairing mode, destructive interaction mode. In constructive interaction mode, which isgood for improving the propulsion efficiency of oscillating foil, the oscillating foil trailingvortex and the vortex in the flow field have the same sense of rotation and merge into a morestrength vortex. In destructive interaction mode, the oscillating foil movement breaks thevortex structure in the flow field and needs to consume more energy. This mode is notconducive to the improvement of the propulsion efficiency of oscillating foil.