Drag Reduction by Dimples on Surfaces in Plane-plane Contact Lubrication

An experimental system was designed to evaluate the drag reduction by dimples on surfaces in plane-plane contact lubrication.Because of the dimples on the surfaces,in some of the experiments,it was observed that gas bubbles existed stably in the lubricant film.The results of the experiments show that the existence of gas was decided by the depth of dimples and the supply volume of lubricant;the deeper the dimples were and the less lubricant there was,the higher the probability of gas existence was.The reason for the existence of gas,based on a model analysis,is the meniscus force of the gas-liquid interface,which caused the gas enclosed in the dimples.In low-oil lubrication,the friction force was reduced obviously because a mixed lubrication film of oil and gas existed,in which lubricant film and gas carried the load together.From the low-oil lubrication to the full film lubrication in plane-plane contact lubrication,an optimal depth of dimples existed,which obviously reduce the friction force.The theoretical analysis result shows that the optimal dimple depth is approximately proportional to the distance between the two surfaces,and it agrees with the experiments.