| Bionics is a new edge discipline, appeared in the middle of last century,that studies the structure, function and working principle of organism, and applies these in engineering technology to create a brand new technology. With the rapid economic development, energy problem is becoming increasingly severe, and resistance is a key factor which causes energy loss. So, drag reduction means energy saving, and all kinds of research of drag reduction technology are constantly being accelerated at home and abroad. Considering all these two effects, inspired by the jet phenomena of shark gills, drag reduction of jet surface is explored based on bionics principle. With the subsidizing of the national science fund project: theory studies on drag reduction characteristics of bionic jet surface (51275102), the thesis mainly studies the related problems of shark gills' structure and bionic jet drag reduction characteristics.First of all, data on the respiratory system of shark were organized, and useful information was extracted. The structure of shark gills and water resistance were analyzed, its respiratory mechanism was researched. Shark swimming in water is similar to submarine, so the resistance of shark could be analyzed by the way in which submarine resistance is calculated. It is found that the resistance of shark in water primarily includes surface friction resistance, viscous pressure resistance and appendage resistance, among which surface friction resistance accounts for more than 80% of the total resistance, and viscous pressure resistance is determined by shark's shape.Then, the jet prototype of shark gills was researched, sharks gills were dissected and analyzed. Through a variety of experimental methods, data related to the thesis was extracted,including shark's breathing rate, the change rule of jet exit, jet angle and velocity, which were obtained from observation experiments, shark's shapes and characteristics, shark gills'characteristics, especially the size, position and arrangement of gill cleft, which were obtained from anatomy experiments. The structure of data was analyzed, and the intrinsic relationship was abstracted to build mathematical model. In addition, the internal structure of gill cleft was observed to extract data. Compared with the existing information, shark's breathing process,channel and mechanisms were analyzed. According to the data collected, a 3D geometric models of shark was built through Proe modeling technology.Next, shark jet model was simulated through CFD technology to analyze the influence of jetting on surrounding flow field. According to the results of numerical simulation, including the value of surface friction resistance, cloud chart of static pressure, shear stress and velocity,static pressure curve of the specified section, the additional functions of shark jet was analyzed. Results show that the jet does have drag reduction effect.At last, the related factors, which influence jet drag reduction effect, were extracted.Combining with the engineering application, plate jet model was put forward based on the shark jet model extracted from experiments. The reliability of numerical simulation is proved through the comparison between theoretical calculation and simulation result. The influence of the changes of the related factors which were obtained from experiments about shark jet on resistance was analyzed to extract the factors that influence drag reduction effect, through numerical simulation technique. Results show that, jet hole position, shape, configuration,angle, and jet velocity will influence drag reduction effect, when the velocity of main fluid field is constant. Among them, the effect of jet hole position, configuration and velocity is more obvious, and it is found that mainstream velocity determines the optimum jet velocity.The research above lays a foundation for further research and application. |
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