Swirling flow with the formation of a precessing vortex core (PVC) in the draft tube model of a hydroturbine was studied. Experiments were performed on an aerodynamic setup under transient operating conditions of the hydroturbine. The turbine operating conditions were varied by continuously changing the flow rate at a constant runner speed. The transition from the partial load regime, when a precessing vortex core is formed, to the best efficiency point without a core is considered. Applied to this task, a comparison of the windowed Fourier transform with wavelet analysis is given. The dependence of the PVC lifetime in the transient regime correlates with the transient time. It is shown that the velocity profiles and the spectrum of pressure pulsations in transient regimes change quasistatically between part-load operation and the best efficiency point of the turbine. The phase-averaged velocity distributions in the transient regimes show that a transient regime is a sequence of quasisteady regimes.

This article is devoted to study the swirling flow with the formation of the precessing vortex core (PVC) in the cone of the model of the draft tube of the hydraulic turbine. The experiments were carried out on the aerodynamic set-up both in stationary and in transient regimes of operation of the hydraulic turbine. The hydraulic turbine operating conditions were varied by continuously changing the flow rate at a constant rotor speed. The formation of the PVC in the flow and the maximum level of pressure pulsations in the regime modeling the partial load regime of a turbine are revealed. The boundaries of the occurrence of the PVC effect are determined with varying rotor speed and air flow rate. It was found that the dependence of the PVC lifetime in transition regimes correlate with the transition time. It was shown that the velocity profiles in transient conditions change quasistatically between the operation regime with partial loading of the turbine and the regime of the highest efficiency of the turbine.

This review addresses the current state of research into active control and suppression of vortex rope in hydroturbines under off-design operating conditions. Only active control methods that can be “switched on” when required under off-design operating conditions are considered in this work. The review focuses on air addition into the flow, as well as various auxiliary fluid jets. It includes all the best practices for vortex rope suppression in numerical and experimental studies. It can be inferred from the review that a modern flow control system should be comprehensive, designed for a specific hydroturbine geometry, and obtain feedback from the flow. Injecting ~2% of air from the impeller fairing cone appears optimal for suppressing pressure pulsations without significant efficiency loss. The cost of air injection is rarely estimated, but the use of an automatic venting system can minimize overheads and potentially improve efficiencies at low gas contents. Fluid jets ranging from 3% to 12% of the main flow rate can efficiently suppress pressure pulsations, but their high energy requirements limit their use. Azimuthal perturbation of the flow appears promising as it does not require significant energy loss, but practical implementation remains challenging as one needs to accurately know the system dynamics and be capable of real-time manipulation of the flow.