Author(s): Daqing Zhou, Jie Zhang
Linked Author(s): Daqing Zhou
Keywords: Francis turbine, labyrinth seals, multi-scale, leakage flow, transition process.
Abstract: For the sake of simplified geometric model and reducing the amount of calculation, labyrinth seals are usually not included in the numerical model of a hydraulic machinery, which consequently affects the results due to the regardless of disc friction losses and volume losses, as well as the pressure fluctuation in the labyrinth clearances. In this paper, we took all the geometrical details of labyrinth seals into consideration and performed multi-flow simulation under the load reduction condition upon a kind of high head Francis turbine using commercial software Ansys Fluent 17. 0. Dynamic mesh and UDF programs were used to realize the motion of guide-vane from 9. 84� to 0. 8�. Firstly, main parameters of the turbine at reduction-load condition were investigated. By comparing numerical results and testing data, we found that calculation values of both torque and discharge were slightly less than the model test with the average value 20 N. m and 10 kg/s, so gap flow through the labyrinth seals needed to be conducted. Secondly, by comparing consequences of Francis turbine with and without labyrinth, the consideration of gap flows in labyrinth seals was proven to have great significance. The prediction of pressure fluctuation of Francis turbine with labyrinth in the vane-less zone and draft tube appears more close to the test data. Moreover, the research found that the maximum force on the top cap and sudden change of pressure in the gap may increase the risk of turbine-lifting and vibration accidents in a hydro plant
Year: 2017