Abstract
Laboratory-based particle image velocimetry (PIV) was used to measure current-driven hydrodynamics within and around a collection of complex obstacles. These obstacles were fabricated using a specialty superabsorbent hydrogel produced through the free-radical copolymerization of sodium acrylate and acrylamide. The optical properties of this gel were found to be nearly identical to those of liquid water. Because of refractive index matching (RIM) of both the fluid and solid media, PIV laser light sheets passed through the obstructions without significant degradation or modification. As a result, all tracer particles suspended in the flow were uniformly illuminated, regardless of their position or proximity relative to individual obstacle features. PIV light sheets were also successfully imaged through the hydrogel, enabling accurate velocity measurement in regions that would otherwise be optically inaccessible. These outcomes were reached without reliance on unconventional fluids or specialized flow facilities. For many experimenters interested in fluid–solid interactions, hydrogel-based RIM may thus be less costly and more adaptable than methods that rely on the existing suite of techniques.
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Acknowledgments
The authors would like to acknowledge ML Byron and EA Variano for their help and generosity. Thanks also go to AB Boehm, CH Fox, R Kopperud, AP Robertson, and B Sabala for their assistance in the laboratory. Support for JSW and RBZ was provided by the Stanford Woods Institute for the Environment. LCS was supported by a DARE Doctoral Fellowship sponsored by the Stanford Office of the Vice Provost of Graduate Education. AEC was supported by a Stanford Graduate Fellowship and a National Science Foundation Graduate Research Fellowship.
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Weitzman, J.S., Samuel, L.C., Craig, A.E. et al. On the use of refractive-index-matched hydrogel for fluid velocity measurement within and around geometrically complex solid obstructions. Exp Fluids 55, 1862 (2014). https://doi.org/10.1007/s00348-014-1862-x
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DOI: https://doi.org/10.1007/s00348-014-1862-x