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ISBN 9783843947992

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978-3-8439-4799-2, Reihe Ingenieurwissenschaften

Eva Schwarz
CFD-based studies of active wind turbine load control by means of trailing edge flaps

186 Seiten, Dissertation Universität Stuttgart (2020), Hardcover, A5

Zusammenfassung / Abstract

One of the main challenges in the development of large wind turbines of 10 to 20 MW size is to reduce the high rotor blade mass. Load alleviation systems are needed in order to enable the construction of lighter blades. An aerodynamic approach for the reduction of fatigue loads is trailing edge flaps on the outer rotor blade part. The local lift can be increased or decreased by deflecting the flap aiming at a constant rotor loading. Several studies have been performed on the concept showing the high potential. Higher-fidelity approaches like CFD were, however, rarely used but are important with regard to the unsteady and 3D effects. This is where the present thesis takes up. The characterization of the dominant aerodynamic effects is performed on simulations of the rigid DTU 10 MW rotor blade with a harmonically oscillating flap. Unsteady airfoil aerodynamics cause the typical amplitude reduction and hysteresis of the load response. The 3D effects on the rotor blade cause a further reduction of the load amplitude due to the influences of flap edge vortices. The decreased efficiency in the flap section is, however, partly compensated by an increased efficiency of adjacent blade sections. Another aerodynamic effect that is of influence at small flap frequencies in the order of 1p is dynamic inflow. An overall assessment of concept requires the incorporation of aero-elasticity since the flap deflection influences the moment coefficient strongly leading to additional blade torsion. The flap influence on thrust and the blade root bending moment is reduced by 20% including blade flexibility in cases with static flap deflection. Two generic inflow scenarios are selected in order to quantify the load alleviation potential in CFD. Load alleviation ranging from 26% to 42% of the blade root bending moment is found. However, these values need to be critically assessed since the simulations miss a power controller and are performed with fixed operational settings.