Session: 10-06-02: Fluid Measurements and Instrumentation

Paper Number: 145695

145695 - Evaluation of a 3d Printed Single Layer Polyvinylidene Fluoride-Trifluoroethylene (Pvdf- Trfe) Sensor as a Wall Shear Stress Measuring Device in High Frequency Oscillatory Flows 

Wall shear stress is a key performance parameter of near wall flow physics occurring on the
surfaces of aerodynamic vehicles and flow surfaces in physiological flow.  Robust methods for
characterizing the structure of turbulent boundary layers are currently needed to resolve engineering
issues such as viscous drag reduction, flow control method failure, and turbine boundary layer
characterization in aerodynamic applications. Over the last decade, there have been various forms
of WSS measuring devices that have been developed for a host of applications ranging from
aeronautics to medical applications. Of these applications, methods such as: oil film interferometry,
optical, floating element, and thermal microelectromechanical systems have been implemented with
a high level of invasiveness and sensitivity to operational environmental factors. For example,
floating element MEMS deliver direct measurement and a high frequency response, yet
measurement efficiency is limited to particulate induced environments for testing and gap
misalignment. These measurement inefficiencies occur after multiple use, exposure to pressure
gradients due to environmental factors, and exposure to cross-axis acceleration and surface
vibrations. Thermal MEMS are difficult to implement, insensitive to two and three-dimensional flow
directions, and have a frequency-dependent response. Optical MEMS, although delivering direct
non-invasive measurements with high frequency response, are difficult to implement, have a large
probe volume, and have accuracy that depends on the properties, size, and number of flow tracers.
Also, MEMS sensors are generally too brittle or fragile for repeated sample attachment or use under
violent flow conditions. Finally, ionic polymer transducers have also been evaluated for sensitivity in
measuring. It has been reported that the thickness of the electrode geometry drastically affects the
output signal. Additionally, these sensors require an exhaustive and expensive fabrication process.
Moreover, none of the existing technologies has demonstrated accuracy better than 10% under
fluctuating shear conditions or deliver direct, dynamic, time resolved WSS measurements with
sufficient frequency response and accuracy to resolve transitional or turbulent flows. Overall, all
existing technologies are incapable of meeting requirements imposed that are needed to resolve the
spatiotemporal unsteady flow characteristics of near wall flow behavior. There is an increasing need
for novel technologies that deliver easy to implement, accurate, robust, time-resolved measurements
of WSS in unsteady flows. PVDF materials have been evaluated for normal stress, pressure, and
WSS measuring studies.  PVDF-TrFe is a flexible polymer, which makes it unique when large
displacements are needed. Key contributions of the proposed work include the following items:
1. Design and fabrication methodology of a novel class of sensors that are produced via PVDF-
TrFe piezoelectric materials for use with dynamic time-resolved direct wall shear stress
measurements.
2. Preliminary evaluation and comparison of the proposed sensors fabrication feasibility and
performance characteristics.
This paper presents the first implementation of a novel class of dynamic time-resolved direct wall
shear stress (WSS) measurement sensors based on 3D printing active Polyvinylidene fluoride
(PVDF-TrFe) piezoelectric materials. These piezoelectric sensors have the advantage that they
contain no moving parts, perform a direct measurement of WSS, and can be mounted directly to the
surface of an existing vessel with no modification to the sensor and produces minimal to zero flow
disturbing effects to surrounding flow environment. The design and development methodology and
characterization of the sensor dynamic signal response are discussed. This work explores a
single layered PVDF-TrFe sensor with painted silver electrodes. The results demonstrate the
potential for using single layer 3D printed PVDF-TrFe sensors to perform accurate, high frequency
measurements of WSS in unsteady flows, especially turbulent boundary layers.

Presenting Author: Sunday Akanji University of North Carolina at Charlotte

Presenting Author Biography: Sunday Akanji is a graduate student in the Infrastructure and Environmental Systems (INES) at UNC Charlotte.
Sunday is involved in research challenges that include the interplay between infrastructure and the environment, contemporary sustainability issues, and renewable energy development. Recently his work has involved developing PVDF-TrFE, ionic polymer metal composites (IPMCs), and dielectric sensors (DEs) as wall shear measuring devices

Authors:

Sunday Akanji University of North Carolina at Charlotte
Dane Lalsen University of North Carolina at Charlotte
Mohammadrafi Marandi University of North Carolina at Charlotte
Tara Cavalline University of North Carolina at Charlotte
Michael Smith University of North Carolina at Charlotte
Rodward Hewlin, Jr. University of North Carolina at Charlotte