Transient LDV-measurements in the draft tube of a high head Francis turbine
Francis-99 is a series of upcoming workshops aimed at determining the state of the art of high head Francis turbine simulations. The scope of this essay is to provide empirical data to serve as validation for the CFD simulations.
Axial and tangential velocity profiles were measured for a model of the Tokke runner while operating in part load, best efficiency, and full load, at two different locations in the draft tube cone: 64mm and 382mm below the draft tube inlet. The results were phase resolved in order to calculate normal Reynolds stresses at the different operating conditions, and the results have been compared with computer simulations. The resulting velocity profiles have been evaluated with respect to the governing equations, and the correlation between velocity profiles, pressure gradients and normal stresses has been discussed. The effect of head on the velocity profiles has been evaluated, and found to have only a small impact on the reduced velocity profiles, both axially and tangentially. The repeatability of the test rig was also tested, and found to be within acceptable limits.
The reliability of the measured velocity profiles is considered high enough to be admissible as validation data for the Francis-99 workshop.
The simulated results show good agreement with the measured velocity profiles for axial flow, but show great discrepancies for the tangential velocity profiles. How- ever, some similarities can be seen between the simulated and measured results, and further work is required in this area.
Place, publisher, year, edition, pages
Institutt for energi- og prosessteknikk , 2014. , 81 p.
IdentifiersURN: urn:nbn:no:ntnu:diva-26064Local ID: ntnudaim:11396OAI: oai:DiVA.org:ntnu-26064DiVA: diva2:744073
Dahlhaug, Ole Gunnar, Professor