Study On Drag Reduction Characteristics And Optimization Of The Riblet Structure For Centrifugal Fan Aerofoil Blade Surface

The energy problem is one of the most important problems accompanied by the national economic development of China and even the world. Energy conservation measures itself, has been regarded as "the fifth energy" by experts, which can greatly reduce the the investment in conventional energy exploitation. While for the fluid machinery, because of the viscous effects, there would be friction produced on the mechanical surface when the fluid flowing through the flow passage, causing the flow loss, affecting the mechanical performance.Drag reduction technology by the riblet structure is derived from the bionics research. It can effectively reduce the frictional resistance by arranging a certain shaped riblet-like structure on the object’s surface. In this paper, by using numerical simulation methods, the drag reduction characteristics of the riblet structure on the surface of flat and the aerofoil blade of the G4-73 centrifugal fan are studied. And based on the analysis and optimization results of drag reduction data on flat surface, the drag reduction characteristics of the riblet structure on the surface of centrifugal fan aerofoil blade are analyzed and optimized.The research results show that the riblet structure on the flat surface can achieve good drag reduction effects. When the "h=s=0.1mm, d=0", the drag reduction effect of the riblet structure is most obvious, the maximum drag reduction rate can reach 3.02%, with the corresponding viscous drag reduction rate of 40.53%. Compared to the smooth surface, the riblet surface increases the pressure resistance and reduces the viscous resistance. As the size of the riblet structure interval increasing, the pressure resistance decreases and the viscous resistance increases. In the riblet structure grooves on the flat surface, there are some stable secondary vortexes formed, acting just like "rolling bearing" effect, which achieve the effect of drag reduction. The vorticity and turbulent kinetic energy and turbulent intensity and wall shear stress and pressure loss of the riblet surface are all lower than the smooth surface, qualitatively reflecting its drag reduction effect. The drag reduction effect would be better when the size of the riblet structure is smaller. And reducing the size of the interval can significantly reduces the wall shear stress and increases the number of the vortices, and the corresponding viscous resistance reduction effect is also enhanced.The riblet structures on the aerofoil blade surface can also achieve good drag reduction effects, and its mechanism of action is similar to the flat surface. Wherein the maximum drag reduction rate is obtained when the riblet structure size is "h=s=d=0.1mm", achieving up to 9.65%, and the corresponding viscous resistance reduction rate is 30.84%, but when the size of the interval "d=0", the universality of the riblet structure is better. Furthermore, when the "h=s=0.2mm", the riblet structure also has a good drag reduction effect. The drag reduction data and various turbulence parameters of the aerofoil blade model all shows that the riblet structure can achieve better drag reduction effects on aerofoil surface than the flat surface.The results of this study can provide a reference for the optimization modification and performance improvement of the mechanical working surface.