Wind turbine aerodynamics using an incompressible overset grid method

    Research output: Book/ReportPh.D. thesis

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    Abstract

    This thesis presents 3D Navier-Stokes simulations of unsteady flow around the two bladed NREL Phase VI wind turbine. The computations are carried out using the structured grid, incompressible, finite volume flow solver EllipSys3D, which has been extended to include the use of overset grids. To handle the relative movement between the rotor and the tower, the domain is decomposed into a number of topologically simple grids that overlap each other arbitrarily. Relative movement of bodies is thus possible without the need for re-meshing. Coupling between overlapping grids is achieved through non-conservative interpolation of the flow variables onto the internal overset boundaries. To satisfy the implicit incompressibility constraint of the pressurecorrection equation an explicit correction of the mass fluxes is employed. The grid assembly and exchange of flow field information is carried out in a fully parallelised environment using MPI.

    Results are presented on the isolated rotor, isolated tower, and on the downwind configuration of the turbine, which includes modelling of the rotor, tower and tunnel boundary layer. The results are compared to previously published computations as well as experimental data from the NREL UAE wind tunnel tests, and are shown to agree very well with both. It is demonstrated that the solver is capable of acurately capturing the unsteady interaction between the rotor and the tower for the downwind configuration. The aerodynamic response of the rotor is characterised by high transient loads on the blades that are strongly influenced by the occurences of blade-vortex interaction. The rotor has a strong effect on the tower shedding, causing vortex lock-in to take place on the upper part of the tower. This lock-in is characterised by a synchronisation of the shedding frequency with the blade passage frequency and a spanwise correlation of the wake.
    Original languageEnglish
    PublisherImperial College of Science, Technology and Medicine
    Number of pages149
    Publication statusPublished - 2006

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