This proposal addresses the grand challenge of enabling, for the first time, direct and simultaneous full-field measurement of the instantaneous pressure and velocity in a fluid flow. The proposed methodology will transform current experimental fluid mechanics practices by providing US academic, industrial, and government institutions with the capability of performing local sensing in real time of kinematics and kinetics of fluid flow fields. While the proposed framework is transformative in nature, its practical implementation requires minimal upgrades to established fluid mechanics measurement systems. Specifically, this proposal encompasses the formulation and incorporation of novel pressure-sensitive tracer particles into traditional Particle Image Velocimetry (PIV) systems towards a novel Particle Image Baro-Velocimetry (PIBV) system. The proposed microcapsules will comprise air encapsulated in highly compliant biocompatible hydrogel shells that are specifically formulated to fluoresce with different wavelength distributions, that is, to change color, depending on the strain of the hydrogel shell. Pressure acting upon the particle modifies its volume, which, in turn, results in a measurable change in the fluorescent response. The response time of the probes to a step change in pressure is expected to be on the order of a microsecond. Further, the hydrogel microprobe design can be tailored to the experiment to optimize sensitivity over a prescribed pressure range and detect pressure levels as low as the order of ten pascals. Utilizing these novel microscale particles as tracers, the velocity field within a fluid can be measured using traditional PIV techniques without a loss of flow tracing fidelity or an increase in overall measurement uncertainty.
Intellectual Merit : The intellectual merits of this project include: (i) establishing a novel measurement system that will enable full characterization of the pressure and velocity fields of complex fluid flow scenarios; (ii) designing, synthesizing, and calibrating a new class of biocompatible pressure microprobes based on hydrogels; (iii) formulating and experimentally validating mechanics-based theoretical and computational models of air-encapsulated hydrogel spheres in fluids; and (iv) assessing PIBV potential through direct pressure measurement in state of the art studies on biomimetic propulsion, hydrodynamic damping, and internal flows.
Broader Impacts : Effective technologies for simultaneous characterization of flow kinematics and kinetics will benefit multiple scientific and engineering communities within academic, industrial, and government institutions and positively impact several applied and fundamental research fields. This project will reinforce technical training and education of the socioeconomically diverse student body in Brooklyn, New York. A suite of teaching modules for middle and high school students demonstrating various principles of fluid mechanics will be developed and implemented in classroom education through synergy with current NSF programs (RET site and GK-12 program). The project will also contribute to the removal of mental barriers across the extremal student populations defining the spectrum of metropolitan versus rural backgrounds in Brooklyn and Waterloo, Ontario by supporting the summer research experience for US students in the University of Waterloo. A one-day instructional short course on PIBV systems will be hosted at the Polytechnic Institute of New York University with emphasis on the measurement principle and uncertainty, data acquisition and processing, and integration into PIV systems. A wiki page about the project will be developed for outreach to the public and promoting PIBV.
