Study on the Effects of Hierarchical Wavy Morphology on Clearance Flow

Clearances broadly exist in hydraulic components, such as the matching clearances of piston/cylinder, swash plate/slipper pad and cylinder block/valve plate, etc., in which most of the energy is dissipated by friction and leakage [1]. With the increasing demand for an environmentally friendly, non-flammable, readily available and hygienic fluid medium in hydraulic systems, water used as a pressure medium has caused renewed interest. However, the kinematic viscosities of water and mineral oil are 1 m2/s and 29 m2/s at room temperature at atmospheric pressure, respectively. Lower viscosity is accompanied by poorer lubricity and larger leakage. For certain matching clearances, the leakage rate of water is larger than that of oil, which will cause more internal and external leakages for water hydraulic systems [2]. Therefore, smaller clearances have to be considered in order to achieve reduced leakage. However, narrower gaps in water hydraulic components will cause mechanical wear [1] and [3] and fluid erosion [4] due to the poor lubrication of water, which will enlarge gaps, leading to more leakage [5]. Surface topography technology has emerged in recent years as an effective method to reduce energy dissipation [6] to [8]. Recent works on various forms and shapes of surface texturing for high efficiency [9] and [10], energy-saving [11] and [12] and long performance life [13] and [14] have been carried out, which has already succeeded in many industrial applications [8], [15] and [16], such as seals [17] and [18], bearings [19] and [20] and gears [21] and [22]. An attempt to optimize piston topography to minimize energy dissipation within the piston cylinder interface was made by Wondergem and Ivantysynova [23] and Ivantysynova [24], who proposed a barrel-like piston. Ivantysynova and Lasaar [25] demonstrated the potential of an advanced gap design using computer simulation. The load carrying ability, piston friction force and gap flow were computed for all investigated surface variations, and then an improved barrel-like piston was proposed to reduce energy dissipation generated by piston/cylinder assembly. Kleist [26] also studied pistons with different shapes for radial piston Study on the Effects of Hierarchical Wavy Morphology on Clearance Flow Zhang, X. – Zhang, T. – Geng, X. – Hong, J. – Wu, J. Xi Zhang1,* – Tianlu Zhang1 – Xiangyu Geng1 – Jianfeng Hong1 – Jinjun Wu2 1China University of Mining & Technology, Beijing, School of Mechanical Electronic & Information Engineering, China 2China Academy of Machinery Science & Technology, China