Two-component instantaneous wall shear rate measurements in reversing flows

TL;DR

This paper validates a two-component inverse algorithm for measuring wall shear rates in reversing flows using electrodiffusion probes, demonstrating good agreement with laser Doppler anemometry and addressing flow unsteadiness.

Contribution

It introduces a nondimensionalization process for ED probes and validates their effectiveness in high-amplitude unsteady flow conditions.

Findings

ED probe measurements agree with LDA results in reversing flows.

The nondimensionalization improves the link between measurements and the inverse model.

The linear velocity approximation is examined in unsteady flow conditions.

Abstract

Validation experiments of the two-dimensional inverse algorithm are performed in a pulsed Poiseuille flow exposing shear reversal phases. The method is applied to the three-segment electrodiffusion (ED) probe for which a specific nondimensionalization process is suggested, allowing to better link measurements from a real ED probe to the modeled one in the inverse problem. This approach provided a two-component wall shear rate in good agreement with the one obtained from laser Doppler anemometry (LDA) measurements, thus validating the ability of ED probes to deal with high-amplitude unsteady flows. The classic linear velocity approximation ($u=sy$) in the probe vicinity is also investigated in such a flow.