Applications of CFD for Flow Rating at Complex Water Control Structures

In this study, computational fluid dynamics (CFD) was used to complement field flow measurements to study discharge capacity of water control structures having complex geometries. The CFD approach described herein is based on solving Reynolds-Averaged Navier-Stokes equations using k-epsilon turbulence model with the free-surface resolved by the volume of fluid method. Two groups of complex water control structures have been investigated as case studies with this hybrid flow rating approach. The first group are the Golden Gate structures which are hinged crest gated structures, also known as pivot weirs. In this paper, a new broad crest weir flow equation which includes a parameterized pivot angle and a modified Villemonte submergence coefficient was proposed. CFD data, in conjunction with field measurement, was used to calibrate the proposed flow rating equations. The methodology proved to be very accurate with an overall error between measured and estimated flows of less than 6% for all three structures. The same approach was applied to Kissimmee River ship locks. In this case, a Villemonte-equation based submergence correction was added to a standard Parshall Flume flow equation for discharge estimation. CFD simulation was then applied to further calibrate the coefficient of this rating formula. Despite limited number of field measurements, a reasonably accurate flow rating equation was obtained. The above cases showed that CFD can be a cost effective, and powerful complementary tool to field measurements to accurately rate water control structures of complex geometries.