Yasunari Kamada

Rotor Blade Sectional Performance Under Yawed Inflow Conditions

This study shows the results of pressure distribution measurements on a rotor blade of a horizontal axis wind turbine under various yawed operations. The experiments are carried out in a wind tunnel with a 2.4 m diameter test rotor. In the measurements, the power curve and pressure distributions are measured for different azimuth angles. By increasing yaw angle, the maximum value of power coefficient of the rotor decreases. The sign of the yaw angle does not have any effect on power performance. The aerodynamic forces are discussed using the axial and rotational force coefficients for each azimuth angle. In the case of higher tip speed ratios, the blade section passing on the upstream side in yawed operations has a greater contribution to the rotor torque than that on the downstream side. In this tip speed range, the aerodynamic forces at the 70% radius section appear proportional to the angle of attack. In the case of the lower tip speed ratios, the blade on the downstream side does not contribute to rotor torque, which appears to result from separation.

Studies on a horizontal axis wind turbine with passive pitch-flap mechanism (performance and flow analysis around wind turbine)

We describe the development of a passive system to control the output power of a horizontal axis wind turbine. This pitch-flap coupling mechanism can reduce rotor power above rated wind speed. This mechanism has two kinds of blade motions: the flapping and the pitching motions. Braking effects are investigated experimentally

Power Augmentation of a HAWT by Mie-type Tip Vanes, considering Wind Tunnel Flow Visualisation, Blade-Aspect Ratios and Reynolds Number

Wind tunnel results are reported concerning the effects of blade aspect ratio and Reynolds number on the performance of a horizontal axis wind turbine (HAWT) with Mie-type1 tip attachments. The flow behaviour around the blade tips and the Mie-type tip vanes is presented. Detailed surface oil film visualization and velocity measurements around the blade tips, with and without Mie vanes, were obtained with the two-dimensional, Laser-Doppler Velocimetry method. Experiments were performed with rotors having blades with different aspect ratio and operating at different Reynolds numbers. The properties of the vortices generated by the Mie vanes and the blade tips were carefully studied. It was found that increased power augmentation by Mie vanes is achieved with blades having smaller aspect ratio and smaller Reynolds number.

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.

Surface Pressure Distribution on a Blade of a 10 m Diameter HAWT (Field Measurements versus Wind Tunnel Measurements)

This paper exploits blade surface pressure data acquired by testing a three-bladed upwind turbine operating in the field. Data were collected for a rotor blade at spanwise 0.7R with the rotor disc at zero yaw. Then, for the same blade, surface pressure data were acquired by testing in a wind tunnel. Analyses compared aerodynamic forces and surface pressure distributions under field conditions against analogous baseline data acquired from the wind tunnel data. The results show that aerodynamic performance of the section 70%, for local angle of attack below static stall, is similar for free stream and wind tunnel conditions and resemblances those commonly observed on two-dimensional aerofoils near stall. For post-stall flow, it is presumed that the exhibited differences are attributes of the differences on the Reynolds numbers at which the experiments were conducted.

Rotor Configuration Effects on the Performance of a HAWT With Tip-Mounted Mie-Type Vanes

In this paper, the relationships between the power augmentation of a HAWT due to Mie-type tip vane application and other factors influencing the efficiency of a wind turbine such as the blade aspect ratio, number of blades, blade pitch angle and Reynolds number are investigated. Experiments were carried out in a wind tunnel with an open, 3.6 m diameter, test section. Rotor models included two- and three-blade upwind turbines with four sets of blades with different aspect ratios. With the rotor blades tested, a maximum power augmentation of about 14.5% was achieved due to Mie vane application. The relationships between power augmentation due to the Mie vane and the above factors are investigated. It is found that the application of a tip-mounted Mie vane results in a larger increase in maximum power coefficient for rotors with smaller aspect ratios and for lower wind speeds. Surface oil film and surface tuft visualization methods were used to detect the flow patterns at the blade tip. Addition of the Mie vanes causes significant changes in flow behavior near the blade tip, resulting in additional blade lift.

Experimental Study of a Straight-Bladed Vertical Axis Wind Turbine With a Directed Guide Vane Row

The objective of this study is to show the effect of guide vane geometry on the performance of wind turbine. In order to overcome the disadvantages of vertical axis wind turbine, a straight-bladed vertical axis wind turbine (S-VAWT) with a directed guide vane row has been proposed and tested by the authors. According to previous studies, it was clarified that the performance of the turbine can be improved by means of the directed guide vane row. However, the guide vane geometry of S-VAWT has not been optimized so far. In order to clarify the effect of guide vane geometry, the effects of distance between the guide vanes and the number of guide vanes on power and torque coefficients were investigated in the experiments. The experimental study was carried out by a wind tunnel. The wind tunnel with a diameter of 1.8m is open jet type. The wind velocity is from 5 to 9 m/s in the experiments. The rotor has three straight blades with a profile of NACA4518 and a chord length of 100 mm, a diameter of 0.6 m and a blade height of 0.7 m. The guide vane row consists of some arc plates.Copyright

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.

Method of Electric Power Compensation for Wind Power Generation Using Biomass Gas Turbine Generator and Flywheel

The power generation using natural energy contains electric power fluctuation. Therefore, in order to put such power generation system to practical use, compensation system power fluctuation is necessary. In this paper, we propose a power compensation method using biomass gas turbine generator and flywheel energy storage equipment. In order to realize high quality natural energy power generation system considering wind power, energy capacity of flywheel energy storage equipment and availability factor of micro gas turbine generator. Usefulness of the proposed system is conformed by experiment using a test plant.

Periodic and aperiodic flow patterns around an airfoil with leading-edge protuberances

Recently leading-edge protuberances have attracted great attention as a passive method for separation control. In this paper, the effect of multiple leading-edge protuberances on the performance of a two-dimensional airfoil is investigated through experimental measurement of aerodynamic forces, surface tuft visualization, and numerical simulation. In contrast to the sharp stall of the baseline airfoil with large hysteresis effect during AOA (angle of attack) increasing and decreasing, the stall process of the modified airfoil with leading-edge protuberances is gentle and stable. Flow visualization revealed that the flow past each protuberance is periodic and symmetric at small AOAs. Streamwise vortices are generated on the shoulders of the protuberance, leading to a larger separation around the valley sections and a longer attachment along the peak sections. When some critical AOA is exceeded, aperiodic and asymmetric flow patterns occur on the protuberances at different spanwise positions, with leading-e...