Flow Characteristics Considering the Temperature Viscosity of Oils in the Gap based on Micro Geometric Roughness Fractal Surface

Due to the limitation of manufacturing conditions in China, the valve core will always exhibit random, disordered and multi-scale micro geometric characteristics in recent years. Based on the fractal features of the micro-scale surfaces of the cores and the chambers of a multi-way valve, this research establishes3-danisotropic models for the surface shapes of the valve cores and chambers using the Weierstrass-Mandelbrot (W-M) function. Then, the boundary conditions of the Navier slip model and computational fluid dynamics (CFD) are used to analyse the flow characteristics of the hydraulic oil in the gap and the wall slip. The research results demonstrate that the surface roughness of the solid walls exerts a significant influence on the flow characteristics of the hydraulic oil as it flows in the gaps: the greater the surface roughness, the higher the probability of occurrence of slip between the surfaces of the solid walls. With varying surface roughness of the solid walls, the greater the slip coefficient b is, the larger the slip velocity on the walls, and the greater the flow velocity of the hydraulic oil in the whole gap; meanwhile, this phenomenon occurs when the temperature difference between the upper and lower walls increases as well, and the flow velocity of the hydraulic oil increases significantly.