Experimental evidence of cavitational effects in a Rayleigh step slider

Abstract

The objective of this article is the study of the load-carrying capacity of a Rayleigh step slider (RSS) for both direct motion (+RSS – which generates lifting effects) and reverse motion (−RSS – which generates suction or cavitational effects). Normal force was measured on a pin-on-disc test rig, with two lubricants (SAE-20 W-50 oil and glycerin) at four speeds and three values of film thickness. During reverse motion (−RSS), cavitational effects have been observed for some test cases. It is supposed that surface tension influences the appearance of cavitational effects, and a modified capillary number, Ca+, is proposed as indicator of cavitation inception. Close-up views taken near the trailing edge of the pin show the occurrence of several streamers, typical for cavitational effects, only when Ca+ > 2. Numerical simulation as well as approximate analytical models are presented for both directions of motion. The comparison of predicted theoretical results with the experimental data is satisfactory.