Junsuke Murata

LDV measurement of boundary layer on rotating blade surface in wind tunnel

Wind turbines generate electricity due to extracting energy from the wind. The rotor aerodynamics strongly depends on the flow around blade. The surface flow on the rotating blade affects the sectional performance. The wind turbine surface flow has span-wise component due to span-wise change of airfoil section, chord length, twisted angle of blade and centrifugal force on the flow. These span-wise flow changes the boundary layer on the rotating blade and the sectional performance. Hence, the thorough understanding of blade surface flow is important to improve the rotor performance. For the purpose of clarification of the flow behaviour around the rotor blade, the velocity in the boundary layer on rotating blade surface of an experimental HAWT was measured in a wind tunnel. The velocity measurement on the blade surface was carried out by a laser Doppler velocimeter (LDV). As the results of the measurement, characteristics of surface flow are clarified. In optimum tip speed operation, the surface flow on leading edge and r/R=0.3 have large span-wise velocity which reaches 20% of sectional inflow velocity. The surface flow inboard have three dimensional flow patterns. On the other hand, the flow outboard is almost two dimensional in cross sectional plane.

Aerodynamic Models and Wind Tunnel for Straight-bladed Vertical Axis Wind Turbines

This paper has attempted to compile the main aerodynamic models that have been used for performance prediction and design of straight-bladed vertical axis wind turbine. Firstly, momentum models (specified as Rotor Blade Model and Streamtube Model) are basically based on calculation of flow velocity through turbine by equating the streamwise aerodynamic force on the blades with the rate of change of momentum of airflow, which is equal to the overall change in velocity times the mass flow rate. And then, according to this theory, Laser Doppler Velocimeter (LDV) was used to investigate two dimensional unsteady flow around Vertical Axis Wind Turbine at three different low tip speed ratios in wind tunnel. In order to clear the characteristics of power coefficient curve, the pressure distribution on the surface of rotor blade were also measured during rotation. Comparing the results, it is concluded that the power coefficient which is calculated from momentum models quantitatively agrees well with the experimental data, except when the blade is at a high tip speed ratio.

Aerodynamic Loads on Horizontal Axis Wind Turbine Rotors Exerted by Turbulent Inflow

†† Wind turbines, which are installed under the natural wind conditions, suffer complicated loads on the rotor blades due to the turbulent wind. The present paper describes a numerical method for calculating the effects of turbulence characteristics on the aerodynamic loads, and shows the numerical results. The turbulent wind field is simulated with the Veers ’ model. This model is based on a Fourier synthesis method and capable of considering spatial crosscorrelations between any two points in the rotor plane, where the turbulent wind is generated. For the calculation of aerodynamic loads on the rotor blades, an inviscid aerodynamic model based on the asymptotic acceleration potential method is adopted.

A numerical method for three-dimensional vortical structure of spiral vortex in wind turbine with two-dimensional velocity data at plural azimuthal angles

A numerical method is presented to extract three-dimensional vortical structure of a spiral vortex (wing tip vortex) in a wind turbine, from two-dimensional velocity data at several azimuthal angles. This numerical method contributes to analyze a vortex observed in experiment where three-dimensional velocity field is difficult to be measured. This analysis needs two-dimensional velocity data in parallel planes at different azimuthal angles of a rotating blade, which facilitates the experiment since the angle of the plane does not change. The vortical structure is specified in terms of the invariant flow topology derived from eigenvalues and eigenvectors of three-dimensional velocity gradient tensor and corresponding physical properties. In addition, this analysis enables to investigate not only vortical flow topology but also important vortical features such as pressure minimum and vortex stretching that are derived from the three-dimensional velocity gradient tensor.

Flapwise and Edgewise Blade Loads Analysis of HAWT Rotor by Using Fluid-Oscillation Coupled Calculation Model

A horizontal axis wind turbine suffers fluctuating aerodynamic loads, which result in oscillations of the rotor blades. Since the blade oscillation has considerable effects on the blade fatigue life, the influence on the fatigue loads from the interaction between the aerodynamic loads and the structural oscillations should be considered in the design process of the wind turbine rotor. The objective of this work is to analyze the aerodynamic effects on the fatigue loads of rotor blade due to structural oscillation and inflow conditions, by using numerical calculation method. This paper explains a calculation model which can estimate the aerodynamic loads on the rotor blade of the horizontal axis wind turbine in the inflow conditions with the turbulence and yawed misalignment. The fluid-oscillation coupled calculation has been performed for the geometry of the NREL test turbine. The calculated results are compared with the experimental results to evaluate the validity of the calculation model.Copyright