Diagnostics of the fluctuating wall shear rate components using an uncalibrated three-segment electrodiffusion sensor

An inverse problem is used to significantly improve the frequency response of a three-segment electrodiffusion (ED) sensor subjected to strong inertial effects in high-amplitude unsteady flows. It is shown that the fluctuating component of the wall shear rate’s magnitude and direction can be accurately determined when both variables exhibit simultaneous large-amplitude variations, even when using an uncalibrated probe. Measurements are performed in the vicinity of a rotating cylinder in motion in a highly viscous fluid with poor electrochemical diffusivity, thus establishing a harsh environment for an ED sensor. Results using the inverse problem showed strong concordance with PIV complementary measurements in most cases and further expose the potential of this non-intrusive technique for thorough wall shear stress diagnostics.