Study On Large Area Molding Technology And Drag Reduction Performance Of Bionic Shark Skin

With the deepening of the research on reducing energy and energy conservation,it has become a hot topic in the drag reduction field that the micro-riblet of shark skin can reduce drag.However,due to the complex structure of the shark skin,it is a great challenge to fabricate high-precision and low-cost bionic shark skin.The micro-riblet structure of bionic shark skin has a better effect on drag reduction.And the roll-to-roll embossing technology has brought great convenience to the large-scale molding of micro-riblet structure.In this paper,the largescale molding of the micro-riblet structure of bionic shark skin has been studied.Firstly,introducing the roll-to-roll embossing experimental principle and experiment equipment,the roll-to-roll embossing experiments of shark-skin-inspired micro-riblet on the surface of PVC and PET films were completed combined with wire winding process.The riblet structure of different sizes can be embossed by using different diameters of steel wire.The experiment uses stainless steel wire with a diameter of 0.5mm and 0.2mm.The results showed that wire winding method can save the development time of the mold,and the roll-to-roll embossing technique realized the continuous large area molding of the micro-riblet structure of the bionic shark skin.Secondly,the influence of process parameters,such as roller temperature,roller speed and compression ratio on the roll-to-roll embossing deforming of polymer films were studied.Combined with materials properties of PVC and PET films,the differences between the two materials were analyzed.The results showed that the roll-to-roll embossing deforming process was dynamic and progressive.The polymer films could emboss better riblet structure under the conditions of suitable temperature,low speed and high pressure.Thirdly,the numerical simulation of micro-riblet drag reduction was performed on basis of the riblets with different depth obtained by roll-to-roll embossing process and the ideal semicircular riblet structure with different diameters.The effect of micro-riblet drag reduction was also analyzed in terms of external disturbances.The results showed that the micro-riblet structure of bionic shark skin performed the effect of drag reduction under a certain flow conditions.And it is the main reason that the vortex structure was uplifted by the micro-riblet structure.Finally,the experiments of drag reduction were conducted in a water tank to verify the effect of drag reduction on the micro-riblet bionic shark skin surface.The micro-riblet bionic shark skin films and smooth films were applied to the surface of the drag reduction model.The resistance on the drag reduction model was measured under different flow velocity and the reduction rate of the micro-riblet bionic shark skin surface was calculated.Results showed that the micro-riblet bionic shark skin surface can perform the drag reduction effect.