49 research outputs found
Tropical cyclone low-level wind speed, shear, and veer: sensitivity to the boundary layer parametrization in the Weather Research and Forecasting model
Mesoscale modeling can be used to analyze key parameters for wind turbine load assessment in a large variety of tropical cyclones. However, the modeled wind structure of tropical cyclones is known to be sensitive to the boundary layer scheme. We analyze modeled wind speed, shear, and wind veer across a wind turbine rotor plane in the eyewall and outer cyclone. We further assess the sensitivity of wind speed, shear, and veer to the boundary layer parametrization. Three model realizations of Typhoon Megi are analyzed over the open ocean using three frequently used boundary layer schemes in the Weather Research and Forecasting (WRF) model. All three typhoon simulations reasonably reproduce the cyclone track and structure. The boundary layer parametrization causes up to 15â% differences in median wind speed at hub height between the simulations. The simulated wind speed variability also depends on the boundary layer scheme. The modeled median wind shear is smaller than or equal to 0.11 used in the current IEC (International Electrotechnical Commission) standard regardless of the boundary layer scheme for the eyewall and outer cyclone region. However, up to 43.6â% of the simulated wind profiles in the eyewall region exceed 0.11. While the surface inflow angle is sensitive to the boundary layer scheme, wind veer in the lowest 400âm of the atmospheric boundary layer is less affected by the boundary layer scheme. Simulated median wind veer reaches values up to 1.7Ă10-2°âmâ1 (1.2Ă10-2°âmâ1) in the eyewall region (outer cyclone region) and is relatively small compared to moderate-wind-speed regimes. On average, simulated wind speed shear and wind veer are highest in the eyewall region. Yet strong spatial organization of wind shear and veer along the rainbands may increase wind turbine loads due to rapid changes in the wind profile at the turbine location.</p
Modal Properties and Stability of Bend-Twist Coupled Wind Turbine Blades
Coupling between bending and twist has a significant influence on
the aeroelastic response of wind turbine blades. The coupling can arise from
the blade geometry (e.g. sweep, prebending, or deflection under load) or from
the anisotropic properties of the blade material. Bendâtwist coupling can be
utilized to reduce the fatigue loads of wind turbine blades. In this study
the effects of material-based coupling on the aeroelastic modal properties
and stability limits of the DTU 10âŻMW Reference Wind
Turbine are investigated. The modal
properties are determined by means of eigenvalue analysis around a
steady-state equilibrium using the aero-servo-elastic tool HAWCStab2 which
has been extended by a beam element that allows for fully coupled
cross-sectional properties. Bendâtwist coupling is introduced in the
cross-sectional stiffness matrix by means of coupling coefficients that
introduce twist for flapwise (flapâtwist coupling) or edgewise (edgeâtwist
coupling) bending. Edgeâtwist coupling can increase or decrease the damping
of the edgewise mode relative to the reference blade, depending on the
operational condition of the turbine. Edgeâtwist to feather coupling for
edgewise deflection towards the leading edge reduces the inflow speed at
which the blade becomes unstable. Flapâtwist to feather coupling for
flapwise deflections towards the suction side increase the frequency and
reduce damping of the flapwise mode. Flapâtwist to stall reduces frequency
and increases damping. The reduction of blade root flapwise and tower bottom
foreâaft moments due to variations in mean wind speed of a flapâtwist to
feather blade are confirmed by frequency response functions