Analytical and numerical validation of a plate-plate tribometer for measuring wall slip

TL;DR

This paper validates a tribometer model both analytically and numerically, confirming the Navier-Slip boundary condition's effectiveness for simulating wall slip and demonstrating minimal impact of inlet variations on measurements.

Contribution

The study provides a comprehensive validation of the DSLT model, confirming the Navier-Slip boundary condition's suitability and showing inlet effects are negligible for accurate slip length measurements.

Findings

Navier-Slip boundary condition effectively models wall slip.

Inlet radius variations have minimal impact on flow results.

Numerical simulations align with analytical predictions.

Abstract

We model the Darmstadt Slip Length Tribometer (DSLT), specially designed to measure viscosity and slip length simultaneously for lubrication gaps in the range of approximately 10 micrometres at relevant temperatures and surface roughness. We investigate the inlet effect of the flow on the results by varying the inner radius of the fluid inlet pipe. The outcomes of numerical simulations suggest that variations in the diameter of this inner radius have minimal impact on the results. Specifically, any alterations in the velocity profile near the inlet, brought about by changes in the diameter, quickly revert to the profile predicted by the analytical model. The main conclusion drawn from this study is the validation of the Navier-Slip boundary condition as an effective model for technical surface roughness in CFD simulations and the negligible influence of the inlet effect on the fluid dynamics between the tribometer's plates.