Study on the Effects of Hierarchical Wavy Morphology on Clearance Flow

This paper aims to explore the influences of multilevel sinusoidal structures on clearance flow by using numerical and experimental methods. A hierarchical sinusoidal morphology was proposed to design the gap between matching surfaces in water hydraulic systems. The specimens with the 0th order, the 1st order and the 2nd order sinusoidal structures were machined by a three dimensional (3D) printer, and their clearance leakage flow was tested on a water hydraulic annular clearance test rig. An extensive simulation study on the effects of waved surfaces with varying amplitudes and wavelengths on leakage was presented. Both the experimental and numerical results show that introducing hierarchical morphology on clearance surfaces will reduce leakage. Moreover, it was found that the leakage decreases with the increase of the ratio of the amplitude to wavelength. Further study of the flow field reveals that the leakage reduction of the 2nd order sinusoidal model is obtained due to the extra vortexes of various scales and the narrower width of the main flow and lower velocity. Moreover, our results indicate that the waved surface induces a micro-hydrodynamic effect that creates an additional load carrying capability, which is helpful for separating the matching surfaces to reduce wear. The study is beneficial to investigate the potential for improving efficiency through the optimization of gap design. Keywords: hierarchical sinusoidal morphology, clearance flow, water, leakage