  Direct dry-cooled power plants typically operate numerous large-diameter
axial flow fans in air-cooled condensers to facilitate the condensation of
steam in the plant thermodynamic cycle. Enhanced fan efficiency may, at scale,
lead to significant parasitic power reductions and subsequent increases in
plant power output. The performance of these fans may be increased by adding
blade tip modifications which act to control blade tip leakage flow. Previous
studies have shown that manipulating the tip leakage vortex increases the
blade-to-air momentum transfer and stabilizes the air flow structures as it
traverses the fan blade. This paper takes a step towards the development of
improved tip vortex manipulators for an ACC fan. Three-dimensional
computational fluid dynamic simulations, and experimental testing of the
modified and unmodified fan within an ISO test facility is performed. The
results are then utilized to assess the accuracy of the simulation model,
visualize the manipulated flow structures at the blade tip, and ultimately
quantify the effect of the endplate designs on fan performance. Excellent
correlation between numerical and test results for the unmodified fan is
observed, and the benefit of blade tip modification on fan performance is again
confirmed experimentally. The simulation model however fails to predict
improvements in fan performance under modification, and simulated tip leakage
flows are investigated for clarification. It is hypothesized that deflection of
tip endplates under operation account for differences between simulation and
experiment, and that fluid-structure interaction analyses could potentially
resolve discrepancies.
