Study On Surface Microstructure Fabricating And Drag Reduction Of Titanium Alloy

Drag reduction technology,as one of the important technical means to achieve energy saving and emission reduction,is a very competitive scientific research,and it is also a research hotspot in various countries.A large number of experimental studies have shown that shark skin has excellent drag reduction performance,so how to replicate the bionic shark skin in a large area,low cost,and efficiently and control its structural parameters after processing is the focus of this research.This paper proposes an efficient,low-cost,environmentally-friendly,and controllable manufacturing method for machining bionic shark skin structures on the surface of titanium alloys based on CNC wire cutting machining technology.1)The principle and advantages of EDM were expounded.Based on the research status of shark skin structure characteristics,a shark skin sample was used as a bionic prototype and its parameters were used to design a bionic shark skin structure.First,through the optimization experiments of electro-machining parameters and analysis of the main electro-machining parameters'impact on surface forming and surface quality,reasonable electro-machining parameters were determined as:pulse width 34us,pulse interval:7,current:2A,feed speed 80mm~2/min.The cutting fluid concentration is 10%.Secondly,three factors are selected to design the sharkskin shield scale structure.Each factor is selected to three levels to study the effect of different structural parameters on the drag reduction effect of the sharkskin surface.The wire cutting machine tool combined with the designed special fixture to process on the surface of titanium alloy,successfully realized the manufacturing of bionic shark skin.2)The characteristics of the surface of the manufactured shark skin were characterized by means of an ultra-depth depth of field electron microscope,SEM,laser confocal,and contact angle measuring instrument.The results show that the morphology,wettability,and chemical composition of the manufactured surface have changed.Combined with the existing theories,the causes of the surface wettability changes are calculated and analyzed in detail,and it is proved that the wetting state is a transition state from C model to W model.In addition,the stability test proves that the surface after manufacturing has good use value.3)Based on Fluent software,numerical simulations of drag reduction were performed on smooth flat plates and three sharkskin-like structures with different parameters.It was found that the existence of the ribbed structure changed the original flow field flow state,which was the main reason for the drag reduction effect on the surface of the shark-like structure.4)A set of macro drag reduction test rigs based on differential pressure resistance measurement method was set up to realize the drag reduction performance test on the surface of titanium and aluminum alloy bionic shark skin.The test bench includes a water inlet device,a macro channel,a pressure measurement device,and a flow measurement device.The flow state was controlled to be laminar,and the drag reduction effect of the bionic shark skin surface under different Reynolds numbers was explored.The test results show that compared with the ordinary smooth surface,the surface of the bionic shark skin has a good drag reduction effect,and the drag reduction rate can reach about 14%under laminar flow.