The aim of the project is to perform experimental tests on a new morphable mini Wells turbine which is particularly suitable to operate in presence of waves with limited energy content. This is the typical scenario which present a high frequency of occurrence along the Mediterranean coasts.
The strengths of this mini Wells are: (i) extremely light rotor; (ii) no need of actuators to morph the rotor blades; (iii) low construction and maintenance costs; (iii) capability to produce energy starting from low wave heights in the order of a few decimetres; (iv) turbine rotors made with non-metallic material. Furthermore, the small size and low investment costs of the turbine make it particularly suitable to be installed either in existing structures, such as anti-reflective perforated caissons (often used in the Mediterranean harbours), or in devices for the coastal defense from erosive phenomena located on shallow water conditions (1.5 ÷ 2.0 m on s.w.l.).
The need to carry out experimental tests derives from the impossibility to handle in a virtual Computational Fluid Dynamics environment the huge difference in time-scale of the turbine (that spins at 1500-3000 rpm) and the wave period (in the order of some seconds). Properly designed lab tests, executed in controlled realistic sea conditions, are therefore mandatory to fully characterized the behavior of morphable WT and its capability to self-starting, that is necessary for operations in the Mediterranean sea.
Technology of Wells turbine is nowadays fully advanced for ocean installation. Plants operating between UK, Ireland and Portugal have reached a reliable level of technology, that unfortunately cannot easily be advanced to exploit scale economies as the OWC-Wells turbine system optimization needs to be tailored to the local sea conditions.
In Mediterranean operations the major open questions are related to:
- self-start capability of the turbine;
- exploitation of morphable rotors to increase efficiency at lower flow rates;
- composite materials required to reach the desired performance;
- coupling with local sea conditions;
- definition of scaling laws for morphable blade rotors;
- definition of scaling laws for OWC-Wells turbine coupling.
The proposed project aims at exploring all these issues and deriving solutions with morphable rotors and a sound design method tailored to various sea conditions. In particular, here the use of a fully-coupled in-house FSI code is completely innovative with respect to the current state of the art of Wells turbine design and verification. Moreover, it is expected that the project will allow to further validate and improve the code by providing reliable experimental data to be compared with the simulation results.
Furthermore, the adoption of fully coupled FSI simulations in turbomachinery is still at its early stages, and the field is still susceptible to further advance and innovations: so far, most of the FSI research was focused on large devices (i.e. wind turbines, large axial fans) manufactured with relatively stiff materials. Indeed, a "weak coupling" approach or modal-based analysis is often preferred in turbomachinery FSI analysis, because the stiffness of the blades is in general very high and the aeroelastic feedback is therefore a secondary effect with respect to the inertial forces. However, some innovative application strictly require a fully coupled technique, which is crucial in order to be able to catch consistently the feedback between the unsteady aerodynamic field and structural response when the structure is particularly flexible: the adoption of this strategy allows us to highlight a large number of unsteady aeroelastic effects, such as flow induced vibration, the insurgence of flutter, and in general, a physically-consistent feedback between the flow and the structure at the interface.
Finally, low stiffness materials are required to obtain a passive adaptive Wells turbine blade, and an early (virtual) evaluation at the design stage of the dynamic behavior for a candidate material can dramatically increase the amount of information available at the design stage, for a given structural configuration, or operating condition, reducing time and costs of the design and test processes.
The main strengths of this research project are made up of:
- the highly interdisciplinary research group from two different departments of the Faculty of Engineering of Sapienza (DICEA and DIMA) able to provide the main technical-scientific skills required for the development of the proposed research. In fact, the research project includes both civil engineering aspects inherent to hydraulics and maritime constructions, and mechanical engineering aspects related to energy aspects and turbines. The research group is composed of professors and researchers who carry out their research activities on issues related to those covered by the request for funding. The research group is completed by two technicians belonging to DICEA (Fabio Sammartino, technical manager of the Hydraulic Construction Laboratory, and Monica Moroni, technical manager of the Hydraulics Laboratory) with proven experience in the experimental field. Both technicians have extensive experience in the field of physical modeling in the hydraulic field and Monica Moroni also in the field of development of measurement techniques;
- the advanced state of development of the proposed device makes it potentially closer to the application/commercial phase;
- the possibility of developing a device for the conversion of wave energy which appears economical, simple and particularly suitable for the wave conditions in the Mediterranean sea. Furthermore, it seems to be easily installable and adaptable to existing port structures which therefore will not require significant investment costs;
- the possibility of including the energy conversion device into coastal protection systems from erosion.