An Overview of Active Control Techniques for Vortex Rope Mitigation in Hydraulic Turbines

Abstract

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.

Passive Control of Vortices in the Wake of a Bluff Body

“…The interaction of vortices with suspended bridges can cause vortex induced vibrations, unless proper mitigating measures are implemented [1]. Rotating vortex ropes in hydraulic turbines at partial load are known to exert pressure pulsations with the risk of detrimental effects on longevity [2]. Secondary flows in blade channels and over blade tips impact negatively the aerodynamic efficiency of turbines [3].…”

Francis Turbine Draft Tube Troubleshooting during Operational Conditions Using CFD Analysis

“…This method has been traditionally used to derive empirical equations for calculating the dimensions of hydropower turbines [4,5]. After significant development in numerical techniques and software since the 2000s, this approach has been widely used not only in the hydropower industry but also in a wide range of mechanical problems from water engineering to mechatronic and even non-Newtonian fluids due to its lower cost and faster results in comparison to experimental techniques [6][7][8][9][10]. Computational tools are particularly suitable for investigating flow distribution, vortex formation, and draft tube vibration in hydropower turbines.…”

Flow Instability Control in a Model Swirl-Stabilized Combustor with Central Jet Injection

“…In the latter case, the effect is referred to as the precessing vortex core (PVC) [3]. The PVC is known to play an important role in the steady or unsteady operation of gas turbine combustion chambers [4][5][6][7], hydro-turbines [8] and other devices with flow rotation.…”