Minu Jeon

Unsteady vortex lattice method coupled with a linear aeroelastic model for horizontal axis wind turbine

Many aerodynamic phenomena on wind turbines are extremely complicated, such as the ground boundary layer effects, directional and spatial variations in wind shear, unsteady yaw effects, and unsteady aerodynamics due to the platform motion of offshore floating wind turbines. Thus, it is unclear whether prediction of the aerodynamic load of a turbine using conventional blade element momentum theory is accurate. On the other hand, this method does not consider unsteady wake effect behind the rotor, the unsteady vortex lattice method can treat non-uniform flow effects derived from the trailing wake from the turbine. Moreover, the aeroelasticity of wind turbines is significant because of the recent scaling up of the turbine size. This induces unsteady aerodynamic phenomena because of fluctuations in the geometrical relative velocity and induced velocity. In the present work, we developed a fully coupled simulation code and analyzed the unsteady aerodynamics of wind turbines by substituting aerodynamic model fr...

Wake Influence on Dynamic Load Characteristics of Offshore Floating Wind Turbines

Because the flow conditions of an offshore floating wind turbine and onshore fixed wind turbine differ, it is debatable whether the aerodynamic load predictions of an offshore floating wind turbine using the conventional blade-element momentum theory, which does not consider the dynamic wake effects, are accurate. Although a generalized dynamic wake method has been developed to consider the dynamic wake effect, it is only stable for lightly loaded wind turbines at high wind speeds. In contrast to the blade-element momentum theory and generalized dynamic wake method, the unsteady vortex lattice method can inherently represent the nonuniform flow effects of the trailing wake from the turbine blades. This paper aims to determine the wake influence of offshore floating wind turbines at low-wind-speed conditions by comparing three wake models: the blade-element momentum theory, generalized dynamic wake method, and unsteady vortex lattice method. The Offshore Code Comparison Collaboration Hywind model is chosen...

Numerical Investigation of Serration Effect on the Helmholtz Resonance

ABSTRACT The flow-excited Helmholtz resonance phenomenon was investigated numerically using Reynolds averaged Navier-Stokes approach. The fundamental cause of the Helmholtz resonance phenomenon is known as shedding of a single discrete vortex from orifice edge that travels during one period of the oscillation. In this study, serrated deflector, which is biomimetic design of the owl’s feather, is used to split a single vortex into small vortices. Rectangular deflector and serrated deflector are com-pared with numerical results of pressure and streamline inside the cavity. Consequently, the serration breaks the shedding period of vortex core and eliminates the resonance. Also, it changes the flow pattern in according to the location of different serration height. By making inflows and outflows occur simultaneously in spanwise direction in the cavity, the period of Helmholtz resonance disappears. Comparing between rectangular deflector and serrated deflector, the serrated deflector can deal with the Helmholtz resonance more effectively.