Efficiency improvement of centrifugal pump with function surface imitating dolphin skin structure

Abstract: In the present study, 2 bionic functional surfaces mimicking from shark skin and dolphin skin respectively were designed and constructed. The simplified riblet mimicking from shark skin was sculptured on the cast iron, and such model was called Model 1 in this study. The riblet was controlled by 3 parameters: the depth of riblet, the aspect ratio and the spacing of riblet. The Model 2 was designed on the basis of Model 1. A layer of elastic material was coated on the Model 1, and this kind of bionic surface was called Model 2. The 200 QJ50-26 type centrifugal pump which was produced by Jilin Aojitong Pump Company, Limited was selected as the implementation carrier of the 2 bionic models, and the study on pump efficiency enhancement by above 2 models was performed in the present paper. There were 3 groups of pumps selected in the experiment. The samples 1 and 2 were the pumps whose impeller surface adopted Model 1, the samples 3 and 4 adopted Model 2 on the pumps impeller, and the sample 5 was a pump with ordinary impeller. The experimental results showed that compared to the sample 5, the pump efficiency of the samples 1, 2, 3 and 4 was all improved effectively in the effective working flow range. The pump efficiency of the samples 1 and 2 was increased by 2%-3%, and the samples 3 and 4 by about 5%. However, the difference was that for the samples 1 and 2, the pump efficiency was enhanced only during the effective working flow range (40-60 m3/h), while the pump efficiency of the samples 3 and 4 was increased in all the flow range from 0-60 m3/h. Above experimental results indicated that the efficiency enhancement effect of the pump mimicking from dolphin skin was obvious. According to the structure of Model 1 and 2, 2 experimental samples were designed and prepared in the flow visualization test, which was performed at the flow speed of 5 cm/s and water temperature of 20℃. The experimental results showed that the distance between wake attachment point and tail for Model 2 was shorter than that for Model 1, which indicated that the negative pressure of Model 2 was lower than that of Model 1. That was to say, the pressure drag of Model 2 was smaller than that of Model 1. In addition, during the experiment, the surface elastic deformation of Model 2 produced by the flow pressure was clearly observed. Furthermore, it was found that the wake vortex spacing of Model 2 was shorter than that of Model 1, which indicated that the wake vortex of Model 1 was generated frequently, and the energy dissipation was higher than that of Model 2. The drag reduction effect of Model 2 was better than that of Model 1. Therefore, the pump efficiency enhancement effect of Model 2 is more effective than Model 1, that is to say, the bionic functional surface mimicking from dolphin skin structure is more effective to improve pump efficiency. The reasons to pump efficiency improvement are that the elastic deformation of surface material which is coupling with the bionic structure together can control fluid medium effectively, inhibit the spread and development of fluid medium disturbance, and reduce the vortex generation density and speed. So, the dissipation of energy is reduced and the drag reduction is achieved.