This paper presents a comparison between the results from numerical modelling and
experiments to
shed light on the mechanisms by which surface texture can reduce friction when applied to an
automotive cylinder liner. In this configuration, textured features move relative to th
e piston-liner
conjunction and to account for this our approach is to focus on the transient friction response to
individual pockets as they pass through, and then leave, the sliding contact. The numerical approach is
based on the averaged Reynolds’
equat
ion with the Patir & Cheng’s flow factors and the
p-
θ
Elrod-
Adams mass-conserving cavitation model. The contact pressures that arises from the asperity
interactions are solved simultaneously to the fluid flow solution using the Greenwood and Tripp
method. The experimental data is produced using a pin-on
-disc set up, in which laser textured pockets
have been
applied to the disc specimen. Under certain conditions
in the mixed and boundary lubrication
regime
s, both model and experimental results show
i
) an increase in friction as the pocket enters the
contact, followed by
ii
) a sharp decrease as the pocket leaves the contact, and then
iii
) a gradual decay
back to the pre-entrainment value. From the evidence obtained for the first time from the proposed
combined modelling and experimental investigation conducted under carefully controlled conditions,
w
e suggest that these three stages occur due
to the following mechanisms:
i
) a reduction in fluid
pressure due to the increased inlet gap,
ii
) inlet suction as the cavitated fluid within the pocket draws
lubricant into the contact, and
iii
) film thickness decay as oil is squeezed out of the contact.
The
interplay of these three mechanisms is shown to control the response of micro-textured surfaces under
all lubrication regimes.