Regimes with high levels of pressure pulsations in the model of Francis-99 hydro-turbine draft tube
The paper reports on the regimes of flow with high level of pressure pulsations in a laboratory air model of the Francis-99 hydro turbine draft tube. Variation of velocity distributions at the model inlet represented 866 regimes under different conditions of turbine load, including regimes with maximal coherent pulsations of pressure on the model walls. We used contact and contactless methods: acoustic sensors to measure pressure pulsations on the model walls and the laser-Doppler anemometer "LAD-06i" to measure averaged velocity distributions. Analysis of the results showed that in the draft tube cone the precessing vortex core (PVC) is formed. PVC is accompanied by a high increase in the amplitude of the coherent pressure pulsations on the walls and the transformation of the averaged velocity field. It is shown that PVC appears when the integral swirl parameters becomes larger than 0,5.