Numerical simulation of part load resonance: comparison of 1D-3D and 1D models

Abstract Partial load resonance, caused by rotation of the draft tube vortex, is investigated using a 1D hydro-acoustic model and a coupled 1D-3D CFD model. Within the 1D model the influence of the draft tube wave speed, the excitation frequency, and the cavity compliance on the amplification factor is investigated. A range of cavity compliance values, corresponding to resonance, is determined. The same operating point was computed using the 1D-3D model for different Thoma numbers. The value of identified cavity compliance, corresponding to the maximum pressure pulsations amplitude is approximately the same as in the 1D model. However, the amplification factor in the 1D-3D model is much lower, than that found in 1D. Two approaches for CFD-based identification of cavity compliance are discussed, and its oscillating nature is highlighted.