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Active Flow Control system FOR improving HYDRaulic turbine performances at off-design Operation

Periodic Reporting for period 2 - AFC4Hydro (Active Flow Control system FOR improving HYDRaulic turbine performances at off-design Operation)

Reporting period: 2020-12-01 to 2021-11-30

AFC4HYDRO is a research and innovation project funded under the European H2020 programme which will develop a new solution to improve the performance of hydropower as a clean and renewable energy source. The main objective of AFC4Hydro is to design and validate an Active Flow Control system in actual hydraulic turbines that permits to operate the units at extreme off-design conditions,
sustain more frequent power ramp transients, achieve higher efficiencies and reduce the maintenance costs. More specifically, deleterious flow phenomena during steady and transient operation including ramping of produced load will be controlled and mitigated to increase turbine reliability and flexibility, and to reduced wear and tear.

This innovative and affordable AFC solution, allowing efficient utilization of existing hydraulic turbines, is planned to be validated at small scale in a model turbine and at large scale in two prototype turbines. For that, this multi-partner project will bring together the expertise and know-how of two universities, Universitat Politècnica de Catalunya in Spain and Luleå University of Technology in Sweden, two of the Europe’s largest renewable energy producers, Vattenfall in Sweden and Statkraft in Norway, a Small and medium-sized enterprise, Flow Design Bureau, in Norway and the Porjus Hydropower Center, in Sweden. This multidisciplinary team makes this project specially interesting because researchers will have the opportunity to test their ideas and concepts not only in laboratory reduced scales but also in full scale prototypes which are the real industrial environments.

A combination of technologies will be used to reduce the pressure and load fluctuations exerted on the machine induced by the draft tube flow using: (1) injection of pulsating momentum (IPM) with a specific frequency, amplitude and phase by means of actuators; (2) injection of continuous momentum (ICM) in the form of water jets with controlled speed and orientation directed against the swirling flow. A structural health monitoring (SHM) system will be developed to evaluate the effects of the injection systems in the structural response of the rotor, generator and bearings. These measurements will be used to optimise the machine performance. For that, a Controller will be programmed and tuned to reduce pressure fluctuations, structural loads and induced vibrations in real-time operation by continuously adjusting the injection systems. The final AFC system will also be tested against demanding transients like ramp up and ramp down. Special attention will be given to mitigate the powerful and dangerous flow instability provoked by the vortex rope breakdown.

The success of the proposal will permit to extend the operating range of already existing turbines beyond the stablished safety limits, to increase their efficiency at off-design operation, to be able to face more frequent transients and to reduce the maintenance and operating costs. As a result, the integration of hydropower in the European energy system will be enhanced, the renewable power system flexibility will be increased, the circular economy will be favoured and the negative effects of the climate change will be reduced.
For the IPM system, a down-scale test rig has been built to characterize the hydraulic behavior of the Porjus U9 downscale runner. The tests carried out have confirmed the appearance of a Rotating Vortex Rope (RVR) at part load as expected and its behavior has been mapped. Various IPM system configurations have been simulated numerically with Computer Fluid Dynamics (CFD) software. The obtained results indicate that the pressure pulsations induced by the RVR can be significantly reduced, which means that in some cases the RVR can be completely mitigated. The IPM has been designed for implementation on the model turbine at Vattenfall laboratory. The commissioning was successfully performed. The preliminary results indicate mitigation of the pressure pulsations in the turbine at different operating conditions. Numerical simulations of the IPM system have also been initiated for Porjus and Oksla prototype test cases.

The ICM development has started by reviewing the existing experience with the 1st generation ICM. An investigation into a specific feature of the ICM technology, namely a protruding nozzle exit, to be added through AFC4Hydro has been concluded positive partly based on modifications of the tools and models recovered in the mentioned review process. This design has met and even improved the objective of having a set of nozzles capable of changing orientation in two planes of rotation. ICM designs for downscale and laboratory scale testing have been manufactured and assembled. The laboratory scale ICM has been tested, and knowledge about ICM performance and operational experience have been gained.

For the SHM system, the UPC test rig has been used to carry out tests for a disk in rotation and submerged conditions. The experimental results have compared well with a numerical model. A set of instrumentation, including innovative fiber optics sensors based on Fiber Bragg grating (FBG) laser technology, has been configured and tested to monitor the fluid and the structure responses. Acquisition routines and online post processing tools have been developed as well as a controller strategy. A new disk has been built to detect cracks on turbine blades. A numerical model of the model turbine has been built and an experimental modal test has been carried out. The SHM has been tested in the turbine model and the preliminary measurements to evaluate the performance of the IPM and ICM systems have been carried. The Porjus prototype rotor has been simulated. The future SHM system for the prototypes is under design. An experimental modal test of the Oksla turbine runner has been carried out.

The development of the controller has started with several tests with the IPM in LTU and at the UPC test rig. In order to build the complete AFC4Hydro system, the interface and communication between the ICM, IPM, SHM and Controller has been defined and stablished. The AFC4Hydro system has been successfully implemented on the model turbine at Vattenfall. The preliminary results indicate mitigation of the pressure pulsations in the turbine at different operating conditions. Meetings have been initiated to discuss the implementation of the AFC4Hydro system in Porjus and Oksla.

The AFC4Hydro project website (www.afc4hydro.eu) and social networks are running with news and blog posts being updated regularly. Three newsletters have been launched and advertised. Two videos have been recorded and published on the website and the YouTube channel, and a third video about the actual measuring campaign has been planned. AFC4Hydro has already taken part in three conferences and has written one magazine article for Enginesoft and one popular science article for Energiteknikk. Two peer-reviewed articles and 11 conference contributions about AFC4Hydro topic have also been published. AFC4Hydro first internal technical meeting and workshop was held by teleconference. Two of the partners have joined national standard committees for initiating the IEC workshop agreement.
• A solution to mitigate the RVR has been experimentally investigated.
• Fiber optics sensors based on FBG technology have been successfully used.
• Novel features have been introduced at the design of the ICM system.
AFC4Hydro simple logo
AFC4Hydro complete logo
Outline of the AFC4Hydro concept with the subsystems