EAGER: A Novel 3-D Printed PVDF-TrFE Copolymer Wall Shear Stress Measuring Device for Measurement of Wall Shear Stress in Unsteady Flow Applications

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Wall shear stress measurements and the influence of shear stresses in aerodynamic and physiological flow applications are vital. Although there is widespread literature in aerodynamic and physiological fluid flow research, many of the basic properties of unsteady flows are poorly understood. A major limitation in the experimental validation of various unsteady flow models is insufficient flow measurement instrumentation, specifically a method of direct non-invasive measurement of wall shear stress. The sensitivity and accuracy needed to evaluate the wall shear stresses in complex unsteady flows is not attainable with the existing state-of-the-art measurement technologies. This research effort aims to investigate a multi-layered 3-D printed piezoelectric polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymer sensor as a wall shear stress measuring device candidate. The proposed technology has an advantage in that it contains no moving parts, can potentially perform a direct measurement of wall shear stress, can be mounted directly to the flow surface with no modification, and can be manufactured easily as compared to existing methods. Preliminary results demonstrate that PVDF-TrFE exhibits exceptional sensitivity to deflection with high accuracy and sensitivity.This research effort will focus on implementing this novel sensor technology to perform direct wall shear stress measurements in unsteady flow applications. This research effort will address issues related to sensitivity, installation of the sensor, validation of sensor measurements with particle imaging velocimetry wall shear stress measurements and with exact analytical solutions for Poiseuille, Womersley and Stokes flows, and issues of error introduced by the sensor thickness. If the proposed effort is successful, the proposed methodology will provide ease of fabrication and implementation for a range of sizes of flush mountable sensors that eliminate moving parts increasing robustness, provides a reduction of cost in flow instrumentation tools, and provides a non-intrusive wall shear stress measurement. PVDF-TrFE sensors have never been tested or used for wall shear sensing, thus the electromechanical coupling mechanism that provides shear transduction is not fully understood. This pioneering research effort will determine the fundamental sensing properties of PVDF-TrFE under wall shear, improve sensor fabrication and packaging, and will develop a methodology for high frequency dynamic calibration.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.