New insights on rotor and stator interactions induced by unstable flows during the turbine runaway transients of three pumped-storage units

Rotor and stator interactions are common unstable phenomena in rotational machinery that can induce complex pressure fluctuations; however, the formation mechanism of some low-frequency rotor and stator interactions between the unstable flow (backflow vortices) and the structural components in the static zone (guide vane) and rotational zone (impeller) is yet to be revealed. To investigate this issue, turbine runaway transients for three pump turbines with different specific speeds were simulated employing one-dimensional and three-dimensional coupled flow simulation methods. The formation mechanisms of pressure fluctuations were revealed by combining time-frequency and internal flow field analyses. The results suggest that, besides the frequency components of the pressure fluctuations induced by the conventional rotor and stator interactions between the structural components (a rotating impeller and a static guide vane), the pressure fluctuations also contained two new frequency components. They were induced by the new rotor and stator interaction between the unstable flow (backflow vortices) and the structural components in the static zone (guide vane) and rotational zone (impeller). The new rotor and stator interaction between the unstable flow and the structural components is defined as the generalized rotor and stator interaction. Consequently, all the frequency components of the pressure fluctuations during the turbine runaway transients of the three pump turbines were attributed to the proposed generalized rotor and stator interaction. They found an important theoretical value in understanding and suppressing the pressure fluctuations in pumped storage units.