Jet flow simulations of Baihetan hydropower station’s discharge surface spillways
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
This project was performed in order to determine if numerical simulations can be used to predict the spreading of a water jet that exits the discharge surface spillways of Baihetan hydropower station. If the spreading ranges can be predicted correctly using numerical simulations, the pressure distribution in the plunge pool downstream the dam can be determined. By being able to determine the pressure distribution, the spillways’ design can then be modified in order to optimize the pressure distribution and thereby minimize the damage on the plunge pool’s river bed. If the spreading ranges can be predicted correctly using numerical simulations it means that numerical simulations can be used as a tool to design future hydropower stations’ discharge surface spillways as a substitute to scale models which are commonly used to optimize the spillway design today.
A simulation model of Baihetan Hydropower station’s discharge surface spillways was constructed. The model was constructed as two separate parts using the pre-processing software Gambit and then imported to the computational fluid dynamics software Fluent for numerical simulation of the water flow. The numerical simulations were performed with a transient flow, the k-ε turbulence model and the Volume of Fluid multiphase model. The models were simulated with a water level in the dam corresponding to when a massive flood has occurred which happens approximately once every hundred years. The results from the numerical simulation were then analyzed with the post-processing software Tecplot 360. Results in form of water spreading ranges when the jet stream hits the plunge pool were obtained from the numerical simulation and compared to data from an earlier performed experimental study where a scale model was used. The water spreading ranges were measured using a water volume fraction of 0-5 percent. The comparison was done to be able to determine if the results from the numerical simulations were accurate enough so that numerical simulations could be used as a substitute to expensive scale models when designing hydropower stations’ discharge surface spillways. A sensitivity analysis was performed where different mesh sizes were used and the Fluent setting double precision mode.
The numerical results were acceptable when checking for convergence, meaning that the equations involved in the simulations were solved properly. The relative difference in water spreading range in the direction of the flow for the Medium mesh size was below 20 percent and thereby considered acceptable while the relative difference in water spreading range perpendicular to the flow was 60 percent for the Medium mesh size and thereby far from acceptable. Possible reasons for these deviations from the experimental results are the approximated uniform velocity profile at the inlet of the spillway and the used k-ε turbulence model. Considering the results obtained in this project, without more detailed study, the numerical simulations using k-ε turbulence model are not advised as a substitute for the experimental methods to determine water flow out of the discharge spill ways of hydropower plants. With more information about the conditions at the inlet and the use of a different turbulence model more accurate results may be obtained.
Place, publisher, year, edition, pages
CFD, Baihetan, spillway, hydropower
IdentifiersURN: urn:nbn:se:umu:diva-106718OAI: oai:DiVA.org:umu-106718DiVA: diva2:844204
Subject / course
Master of Science Programme in Energy Engineering
Nair, Gireesh, Universitetslektor
Eklund, Robert, Universitetslektor