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

Periodic Reporting for period 1 - AFC4Hydro (Active Flow Control system FOR improving HYDRaulic turbine performances at off-design Operation)

Reporting period: 2019-06-01 to 2020-11-30

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.
In order to develop the IPM system, a new down-scale test rig consisting of a reduced scale turbine has been built which improves the performance of an old one already existing. The hydraulic behavior of the Porjus U9 downscale runner has been characterized. 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 in both the new and the old down-scale test rigs. 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 same IPM designs have been developed and tested at the old test-rig and the results have confirmed the simulations.

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. A conclusion partly based on modifications of the tools and models recovered in the mentioned review process. Based on this 1st ICM design, and possibly the one to be favored in several iterations through the project lifetime, has come to life. This design has met and even improved the objective of having a set of nozzles capable of changing orientation in two planes of rotation. Most parts have been ordered and the manufacturing and assembling tasks have already started. As soon as the ICM is ready it will be tested in the new down-scale test rig.

In order to develop the SHM system, a new test rig to study fluid structure interaction phenomena in submerged rotating systems has been designed, manufactured and built. The new platform is now operational. A complete set of instrumentation to monitor the desired magnitudes for both the fluid and the structure domains has been chosen, purchased, configured and tested. In particular, an experimental validation of innovative fiber optics sensors based on Fiber Bragg grating (FBG) laser technology for dynamic tests of submerged structures has been performed. A numerical model of the system under study in the new test rig has been built. In addition, a complete numerical model of the Vattenfall turbine test stand has been built and the modes of vibration have been obtained. Finally, the Porjus U9 generator has also been modeled and simulated. To validate the numerical models, several experimental modal analyses are starting to prepared and some tests have been carried out.

The development of the controller has started with several tests with the IPM at the old down-scale test rig in LTU and at a simple beam submerged in water at UPC. 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 project web-site and social networks are running with news and blog posts being updated regularly. The first newsletter has been launched and advertised. Two videos have been recorded and published on the web-site and the YouTube channel. AFC4Hydro has already taken part in three conferences. And finally, two of the partners have joined national standard committees for initiating the CEN/CENELEC workshop agreement.
At the end of month 18, the following progress has been achieved:
• Better understanding of the needs to mitigate the RVR has been acquired.
• A solution to mitigate the RVR has been proposed and defined.
• Fiber optics sensors based on FBG technology have been successfully used in a dynamic test of a submerged structure.
• Novel features have been introduced at the design of the ICM system that might enable a more compact and less expensive control.
These improvements, some of them exceeding the project proposal, will guarantee the achievement of the objectives to control the flow and will make the results ready for higher TRLs.
AFC4Hydro simple logo
AFC4Hydro complete logo
Outline of the AFC4Hydro concept with the subsystems