Bionic Squid Propulsor And Research On Its Hydrodynamic Simulation And Experiments

After millions years of evolution, aquatic animals possess superb swimming skills and incredible efficiency, squid is the outstanding kind. With the development of machinery, materials and control theory, development of bionic underwater robot imitating aquatic animals as squid becomes possible. Squid is the main research object, including their biological morphology, physiology structure and movement characteristics. Bionic squid underwater propulsors actuated by shape memory alloy (SMA) wires are investigated. Experimental testing and computational fluid dynamics simulations are use to study its hydrodynamic performance. The research not only helps to understand the mechanism of swimming squid, but also can provide components and theoretical basis for bionic squid underwater robots.Vortex ring is a common phenomenon which plays an important role in aquatic animal propulsion. Aquatic animals have several propulsive modes. Vortex formation mechanism and its effect on swimming efficiency are analyzed. Squid possess composite propulsive modes including level fin and jetting. It can adopt different swimming modes according to different conditions, with a strong ability to generate and control vortex ring. It has many merits: high speed, good maneuverability and high efficiency. One reason why squid can achieve high-speed is perfect streamlined body. Three-dimensional squid model was established according to the anatomy of the physical parameters of squid. Squid's swimming strategy and its hydrodynamics are comprehensively analyzed. Turning control is a important measure to scale mobility and squid possess several turning patterns. Its flexible turning control surface based drag is detailed analyzed, which has better performance comparing with rigid steering.As a new actuator material, SMA wires begin to be widely used. In order to verify the feasibility of using SMA wires to simulate squid or fish muscles, SMA wires is initially tested on a performance testing platform. The strain (close to 4%) and stress (800 Mpa) are sufficient to meet the design requirements. Flexible bending with large amplitude is basic movement for fins in fish or squid. Based on their muscle action principles, a caudal fin propulsor and a triangular pectoral fin actuated by SMA wires are investigated. The open-loop control experiments on these two propulsors show that they have merits: high degree of flexibility, smooth action with large amplitude and zero noise. Then the unsteady propulsive forces of the propulsors are measured. The maximum instantaneous thrust for caudal fin propulsor is up to 15.8 mN, and 102.5 mN for the pectoral fin. The unsteady thrust variation with bending angle is obtained, and the impact of bending angle, frequency, shape and size on propulsive performance is researched.As the experimental testing, CFD simulation is another effective mean to study the mechanism of biological swimming. Firstly, CFD simulations are used to verify the perfect body shape of squid and their ascendant flexible turning control surface. Secondly, approximate kinematics models are set up based on the action experiment on the caudal fin propulsor and trigonal fin propulsor. Dynamic mesh technique is used to simulate the movement of the propulsor in 2D and 3D respectively. Though the simulation, the change character of unsteady force and the impact of bending parameters on average thrust force are received. The simulation results accord with the experimental results well. The phenomenon of vortex ring is found in the 2D simulation of caudal fin, just similar with live fish. Quantitative analysis is carried out on the vortex ring. Strouhal number (St) characterizes the unsteady effect of fluid. Fish can achieve most effective propulsion when 0.2≤St≤0.3. In simulation, the background flow is used to replace the forward movement of the caudal fin. The effect of St on the vortex wake is simulated. The wake presents intermediate state between drag wake and thrust wake when 0.2≤St≤0.3. To further verify the the visual flow field generated by numerical simulation, a flow level visualization system is built based on modified PTFE powder. A visual research on vortex ring formation process generated by tail propulsor is carried out on the system, which can provide accurate flow field.The power source of rapid swimming squid is jetting water. A bionic squid pulse jet propulsor actuated by SMA wires is investigated and experimentally tested. The experiments explore the impact of the amplitude of bionic mantle, action speed and nozzle diameter on propulsive performance. .Then a similar jetting model is established and simulated by CFD. The simulation focuses on the formation process of vortex ring jet from the mantle. The impact of the vortex formation number (L/D) on jetting wake and the change character of thrust force are analyzed. The results verify vortex ring mechanism and jetting strategies in squid propulsion.In summary, the experimental testing and simulation on the bionic squid propulsor provide effective theoretical and experimental research platform.