Relations Between The Vortex And Pressure Fluctuation In Draft Tube Of The Hydraulic Turbine

This dissertation adopts fluid motion simplification method to study and qualitatively analyze the inception of draft tube pressure fluctuation and influential factors. Use CFX5.5 software to simulate steady and unsteady turbulence flows in Francis model turbine. At last the results of draft tube flow field characteristics, vortex distribution condition, amplitude and frequency of pressure fluctuation.were obtainedBased on the fluid motion simplification method, this dissertation analyzed the inception of draft tube fluctuation, took the flow state, before and after runner, as simulation objects, simplified the Euler equation, thus found out the location of fluctuation energy. Furthermore qualitatively analyzed the inception of draft tube pressure fluctuation, simplified the outlet circulation calculation equation which cause the draft tube pressure fluctuation, also simplified the frequency and amplitude equations of pressure fluctuation. The experimental results showed that this dissertation has certain practical importance for qualitatively analyze draft tube pressure fluctuation. Besides, introduced the simulation method of 3D simulation of draft tube flow, constructed the geometric model of draft tube, obtained draft tube pressure fluctuation time domain chart also the shape and frequency characters of vortex, the results showed that the simulation is resemble to practical condition, also proved the correctness of the simplified equations.This dissertation simplified and derived the frequency and amplitude calculation equations of pressure fluctuation character parameters. After calculating practical examples and comparing the simulation results and experimental results, this method has been proved to be feasible. Under partial load conditions the draft tube 3D simulation results showed that the climax of pressure fluctuation of draft tube vortex incepted at the underside of cone part closed by bend and the frequency of the pressure fluctuation accorded with times frequency rule very well.