Lessons learned in stepped chute research instrumentation

Authors: Hunt, Sherry; Kadavy, Kem

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2021
Publication Date: 5/21/2021
Citation: Hunt, S.L., Kadavy, K.C. 2021. Lessons learned in stepped chute research instrumentation. Applied Engineering in Agriculture. 37(3):513-521. https://doi.org/10.13031/aea.14333.
DOI: https://doi.org/10.13031/aea.14333

Interpretive Summary: Instrumentation plays a vital role in developing design criteria for embankment dam structures. All instruments have their advantages and disadvantages. For instance, one instrument may be used in water flow without the presence of air, while another requires air to be in the water. Research conducted on a staircase type concrete structure was tested with three types of instrumentation. One instrument could only record data if no air was present in the flow. Another one performed well with no more than 30% air present, and the last instrument could only collect reliable data when air was in the water. Lessons were learned on the operation and performance of these instruments through data comparison. These findings are intended to help other researchers interpret their data.

Technical Abstract: Design procedures for hydraulic structures like stepped chutes has depended on quality data from physical model studies. While designers have turned to computational fluid dynamic (CFD) models in more recent years as a cost saving method over physical models, data from physical models are necessary for engineers to feel confident with CFD models. For decades, researchers worldwide have been examining non-aerated and aerated flow conditions in stepped chutes, and the impact these flows have on stepped chute design, associated stilling basins, and downstream rock aprons. A variety of instruments have been used in these structures to capture clear water and bulked flow depths, velocities in non-aerated and aerated flow regions, and air concentration data. The objective of this paper is to provide some lessons learned on the operation and performance of these instruments, and how data compares between differing instruments, operators, and physical model facilities with varying design parameters (e.g. chute slope, step height, unit discharge, etc). Significant findings are 1) an acoustic Doppler velocimeter, a standard Pitot tube, and a RBI fiber optic probe performed as expected, 2) a Pitot tube is not suitable for aerated flows where air concentration, C > 0.3, 3) errors observed in the dimensionless velocity data near the pseudo-bottom for a Pitot tube and fiber optic probe occur at y < 0.25ks, and 4) data throughout stepped chute literature appear to show similar trends indicating the repeatability in comparable instrument performance.