Performance improvement of the biradial self-rectifying impulse air-turbine for wave energy conversion by multi-row guide vanes: Design and experimental results

• Published in: Energy (Oxford) 2021-02, Vol.216, p.119110, Article 119110
• Main Authors: Gato, L.M.C., Maduro, A.R., Carrelhas, A.A.D., Henriques, J.C.C., Ferreira, D.N.
• Format: Article
• Language: English
• Subjects: Air turbine; Axial flow; Biradial turbine; Cascade flow; Converters; Design; Design optimization; Design techniques; Energy conversion; Evolutionary algorithms; Guide vanes; Guide-vane design; Impulse turbine; Misalignment; Outflow; Rotors; Stalling; Topology; Turbines; Water circulation; Water wells; Wave energy; Wave power; Wells turbines
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2020.119110

Self-rectifying impulse turbines are a popular alternative to the Wells turbine for oscillating-water-column wave energy converters. Self-rectifying impulse turbines have two sets of guide-vanes, one set placed symmetrically on each side of the rotor, instead of a single set as in unidirectional turbines. The efficiency of self-rectifying turbines with fixed guide-vanes is known to be severely affected by the large aerodynamic losses due to the inherent misalignment between the outflow from the rotor and the downstream guide-vanes. The biradial turbine is an advanced, more efficient, version of the impulse self-rectifying turbine, as compared with the conventional axial-flow type. The paper presents a new topology for the radially-set guide-vane system arranged into multiple, rather than simple, rows, aiming to increase the turbine efficiency by reducing the losses by aerodynamic outflow stalling at the exit guide-vane system while ensuring the required inflow deflection by the inlet guide vanes. The design method combines an evolutionary optimisation algorithm with cascade-flow CFD RANS calculations. Experimental results are presented to validate the design method and to assess the performance and flow-losses of the single and double-row guide-vane system configurations. •Single-row stator configuration high blockage severely penalises turbine efficiency.•Multiple-row guide-vane systems reduce rotor outflow obstruction.•Turbine peak efficiency increased by using a novel double-row guide-vane system.