Analysis of pressure oscillations in a Francis hydraulic turbine with misaligned guide vanes

Abstract

Three-dimensional unsteady turbulent flow in the entire flow passage of a model Francis turbine is simulated by adopting the realizable k-ε turbulence model. Using experimental data, the validity of the mathematical model is verified. Pressure oscillations are calculated for a model turbine attached with a misaligned guide vanes (MGV) device. Two MGV with five different MGV opening angles are selected for analysing the influence of MGV on pressure oscillations in the spiral case, guide vanes, runner, and draft tube. The computational results show that (a) the rotational frequency of the vortex rope remains unchanged despite different MGV openings, (b) the MGV device changes the peak-to-peak amplitude in a similar way as aligned guide vanes, (c) with increasing MGV opening, the amplitude of various frequency components in the draft tube vary in different ways, (d) a new frequency that is the product of the runner frequency and the number of MGV appears in the runner, and (e) with increasing difference between the MGV opening and the other guide vane openings, the amplitude of this new pressure oscillation increased.