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Accueil > Actualités > Séminaires > Séminaires 2021

Mardi 5 Octobre 11h00 - LEGI Salle K118

Stefan Hoerner, Laboratory of Fluid Mechanics and Technical Flows University Otto-von-Guericke Magdeburg

Title : Cross-flow tidal turbines with flexible rotor blades – an experimental approach

Contact : Pierre-Luc Delafin

Abstract : Cross-flow tidal turbines, also called vertical-axis turbines, suffer from alternating structural loads and a low turbine efficiency due to cyclic flow separation and dynamic stall. This is the major drawback of this otherwise promising technology for the exploiting tidal streams with highest area-based power density in farm installations. It can be seen as key challenge to be solved for a broad industrial application.

In order to investigate the highly dynamic processes at the blades, a large number of experiments were performed. It was shown that a hyperflexible blade structure leads to an adaptation of the blade morphology to the flow and enables passive flow control. By mitigating stall, this leads to lower structural loads and higher blade thrust. However, successful implementation requires blade stiffness well matched to hydrodynamic loads, and the benefits depend on the operating point. The experiments characterize the underlying fluid-structure interaction, based on a surrogate model of a pitching hydrofoil in the closed-loop hydrodynamic tunnel at the LEGI lab in a parametric study. Three blade stiffnesses were investigated for two operating points and multiple designs of varying turbine solidity. In addition to a 2D2C high-speed PIV measurement, tech niques to measure the structural deformations and hydrodynamic loads were developed and embedded in a fully automated experimental design. The methods include structured-light based 3D deformation tracking, 2D cross-section tracking from PIV raw data (both were included in the fluidimage framework) and hydrodynamic load acquisition using a six-axis load cell.

The findings allow for linking hydrodynamic forces with structural deformation and flow field. They show a promising approach for an improved rotor design with longer life-cycles (due to reduced loads) and higher turbine efficiencies.