Xabier Munduate

Three-dimensional and Rotational Aerodynamics on the NREL Phase VI Wind Turbine Blade

This work undertakes an aerodynamic analysis of the NREL NASA Ames wind tunnel data, namely the Phase VI Unsteady Aerodynamic Experiment. The experimental sequences selected here for this study respond to the parked blade and the rotating configuration, both for the upwind two-bladed wind turbine operating at non yawed conditions. The objective is to bring some light into the nature of the flow field and especially the type of stall behaviour observed when compared the 2D aerofoil steady measurements to the parked blade and the later to the rotating data. From averaged and instantaneous pressure coecients together with their standard deviations values, the corresponding trailing edge flow separation and leading edge reattachment points had been pinpointed, with the limitations of the repeatability of the flow encountered on the blade. Results for the 3D parked blade show the progressive delay of the trailing edge separation process, with respect to the 2D profile, and also reveal a local region of leading edge bubble separated flow, at the inner parts 30% and 47 % of the blade. For the 3D rotating blade, results at inboard stations 30% and 47 % show a dramatic suppression of the trailing edge separation, and the development of a quasi-steady leading edge separation phenomena responsible for the extra lift. At the 63% and 80 % rotating blade sections, the averaged pressure coecients are not representative anymore of a steady behaviour, and their instantaneous pressures values for a given incidence are highly unstable, showing gross changes in an oscillating flow pattern.

Aerodynamic Thrust Modelling in Wave Tank Tests of Offshore Floating Wind Turbines Using a Ducted Fan

Wave tank testing of scaled models is standard practice during the development of floating wind turbine platforms for the validation of the dynamics of conceptual designs. Reliable recreation of the dynamics of a full scale floating wind turbine by a scaled model in a basin requires the precise scaling of the masses and inertias and also the relevant forces and its frequencies acting on the system. The scaling of floating wind turbines based on the Froude number is customary for basin experiments. This method preserves the hydrodynamic similitude, but the resulting Reynolds number is much lower than in full scale. The aerodynamic loads on the rotor are therefore out of scale. Several approaches have been taken to deal with this issue, like using a tuned drag disk or redesigning the scaled rotor. This paper describes the implementation of an alternative method based on the use of a ducted fan located at the model tower top in the place of the rotor. The fan can introduce a variable force that represents the total wind thrust by the rotor. A system controls this force by varying the rpm, and a computer simulation of the full scale rotor provides the desired thrust to be introduced by the fan. This simulation considers the wind turbine control, gusts, turbulent wind, etc. The simulation is performed in synchronicity with the test and it is fed in real time by the displacements and velocities of the platform captured by the acquisition system. Thus, the simulation considers the displacements of the rotor within the wind field and the calculated thrust models the effect of the aerodynamic damping. The system is not able currently to match the effect of gyroscopic momentum. The method has been applied during a test campaign of a semisubmersible platform with full catenary mooring lines for a 6MW wind turbine in scale 1/40 at Ecole Centrale de Nantes. Several tests including pitch free decay under constant wind and combined wave and wind cases have been performed. Data from the experiments are compared with aero-servo-hydro-elastic computations with good agreement showing the validity of the method for the representation of the scaled aerodynamics. The new method for the aerodynamic thrust scaling in basin tests is very promising considering its performance, versatility and lower cost in comparison with other methods.

Unsteady modelling of the oscillating S809 aerofoil and NREL phase VI parked blade using the Beddoes-Leishman dynamic stall model

An implementation of the Beddoes-Leishman dynamic stall model has been developed at CENER, for modelling the unsteady aerodynamics on oscillating blade sections. The parameters of the model were adjusted for the S809 aerofoil, using an optimization based on genetic algorithms, and taking into account the values found in the literature and the physics of the aerodynamic process. Once the parameters were fixed to a unique set, oscillating cases of the 2D S809 aerofoil were computed, and compared with experimental data. Thus, the accuracy of the model was evaluated. On the other hand, oscillating cases of different span stations of the NREL phase VI parked blade were computed and compared with experimental data, to analyze the three-dimensionality of the dynamic stall on the blade sections. For the unsteady computations on the blade, the model was fed with the steady data of the blade section, to directly consider the geometry influence. In general, the results of the computations for the 2D aerofoil and 3D blade sections were very encouraging.

CFD and aeroelastic analysis of the MEXICO wind turbine

This paper presents an aerodynamic and aeroelastic analysis of the MEXICO wind turbine, using the compressible HMB solver of Liverpool. The aeroelasticity of the blade, as well as the effect of a low-Mach scheme were studied for the zero-yaw 15m/s wind case and steady- state computations. The wake developed behind the rotor was also extracted and compared with the experimental data, using the compressible solver and a low-Mach scheme. It was found that the loads were not sensitive to the Mach number effects, although the low-Mach scheme improved the wake predictions. The sensitivity of the results to the blade structural properties was also highlighted.

3D Dynamic Stall Modelling on the NREL Phase VI Parked Blade

This paper presents an experimental and modelling analysis of the unsteady aerodynamics, including dynamic stall, on sections of the NREL phase VI parked blade. The analysis is reduced to integrated normal force and moment coecients. Considering that the NREL phase VI blade uses exclusively the S809 aerofoil on its sections, experimental sinusoidal oscillating tests of the 2D S809 profile have been used as baseline. First, the unsteady cases of the 2D aerofoil are compared with the unsteady results of the 3D parked blade sections, both experimental data undergoing the same pitching oscillations. Following, the unsteady cases of the parked blade sections are presented together with the computations of CENER’s Beddoes-Leishman implementation. This method relies on the aerodynamic steady data: force and moment coecients, as input to predict the unsteady cases. Thus, two approximations have been carried out for the computations, firstly using the steady data of the 2D S809 aerofoil as input, and secondly using the steady data of the corresponding NREL blade sections to nourish the calculations. The encouraging results obtained with the last approximation show that the three-dimensionality of the dynamic stall on the parked blade is strongly managed by the steady behaviour of the blade sections.