A water turbine runner is exposed to several perturbation sources with different frequencies, phases, and amplitudes both at the design and off-design operations. Rotor-stator interaction, cavitation, rotating vortex rope, and blade trailing edge vortices are examples of such perturbations which can disturb the runner. The rotor dynamic coefficients require being determined to perform a reliable dynamic analysis. Fluid added inertia, damping, and stiffness have previously been investigated for individual perturbation frequencies for the torsional vibration of a Kaplan turbine model runner. However, a number of perturbation sources mostly take place simultaneously and alter the dynamics of the runner. Soltani et al. [1] have evaluated the torsional added parameters for a Kaplan turbine runner using numerical simulations considering single perturbation frequency. In the present work, the fluid added parameters are assessed in the presence of multiple perturbation sources. A similar methodology is used. A single-degree-of-freedom (SDOF) model for the dynamic model and unsteady Reynolds-averaged Navier-Stokes approach for the flow simulations are assumed. Perturbations with different frequencies are applied to the rotational speed of the runner to determine the fluid added parameters for the torsional vibration. A number of previously investigated frequencies are chosen and their combinations are investigated. In addition, two different phase shifts are considered between the applied perturbations to study the effect of phase. Two more test cases with higher perturbation amplitude are also conducted to investigate its influence on the fluid added inertia and damping. The results are compared with the previous study and the interaction of multiple perturbations on the added parameters is investigated.
