Abstract
In any hydraulic machine there are lubricated couplings that could become critical beyond certain operating conditions. This paper presents the simulation results concerning textured surfaces with the aim of improving the performance of lubricated couplings in relative motion. The texturing design requires much care to obtain good improvements, and it is essential to analyze both the geometric features of the dimples and the characteristics of the coupled surfaces, like the sliding velocity and gap height. For this purpose, several CFD simulations have been performed to study the behavior of the fluid bounded in the coupling, considering dimples with different shapes, size, and spatial distribution. The simulations consider the onset of gaseous cavitation to evaluate the influence of this phenomenon on the pressure distribution generated by the textured surface. The analyses have pointed out that it is critical to correctly predict the behavior of the textured surface in the presence of local cavitation, in fact, when cavitation occurs, the characteristic time of the transient in which the phase of the fluid change is very rapid and it is comparable to the time taken by the fluid to move from one dimple to the next.
Highlights
In hydraulic machines, metallic surfaces in relative sliding motion are widespread and hydrodynamic effects are useful to support heavy loads, due to operating conditions and to limit surface wear
To analyze the behavior of a textured surface, the investigation has been initially focused on a single dimple case to understand what dimple geometry permits to obtain better improvements
A square-shaped dimple has been assumed as reference geometry
Summary
Metallic surfaces in relative sliding motion are widespread and hydrodynamic effects are useful to support heavy loads, due to operating conditions and to limit surface wear. Texturing a surface means to realize a precise and ordered micro-geometry on a surface to increase the tribological properties [1]. The geometric effect generates a greater hydrodynamic bearing capacity, due to an increase in the average pressure that is established between the moving surfaces. A lower friction coefficient could be obtained, since there is a smaller contact area and a greater average gap, reducing the overall surface wear. Yu et al [2] have presented a numerical study on the influence of dimples’ shape and orientation on the load capacity and the friction coefficient, reaching good results in terms of tribological improvements
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