Approach

The approaches in Mexnext-I, Mexnext-II and Mexnext-III are very similar but Mexnext-II and Mexnext-III start with an inventory of the 'unexplored' experiments.  Apart from that all  Mexnext phases  are carried out along the following Work Packages.

WP2: Processing/presentation of data, uncertainties, tunnel effects
Data will be processed and uncertainties will be assessed. An assessment will, if applicable, also be made for the wind tunnel effects

WP3: Comparison of calculational results from different types of codes with measurement data
In this WP the calculational results from the codes which are used by the participants are compared with the data from the various experiments. It is meant to be a thorough validation of different codes and it provides insights into the phenomena which need further investigation (see WP4).

A unique feature of the Mexico experiment was that both detailed aerodynamic measurements along the blade as well as flow field data were taken. Therefore in Mexnext-I the following data could be compared:

Pressure data
Normal force coefficients
Tangential force coefficients
Balance data
PIV data

Note that the data to be compared depend on the type of code (e.g. a BEM code cannot produce pressure data).

In Mexnext-III  it is anticipated that again in both the pressures along the blade as well as flow field data can be compared. The advantage of the comparison with New Mexico data lies in the fact that more data are available at a higher quality

WP4: Deeper investigation into phenomena
In this Work package a deeper investigation of different phenomena will take place.
The phenomena will be investigated with isolated submodels, simple analytical tools or by physical rules.

Task 4.1: Standstill
Parked conditions are amongst the design driving load conditions (storm loads). Several measurements have been carried out at standstill and a large number of pitch angles. The resulting loads will be analyzed and compared with common design standards. It is furthermore expected that these data form a reference for the rotational measurements in order to distinguish rotational effects. It was decided to combine this task with task 4.12 (IEC Aerodynanamics)

Task 4.2: Sensitivity of results on Reynolds number
A number of measurement campaigns have been performed at various rotational speeds where the remaining conditions are more or less similar. As such a comparison of the results at the two rotor speeds may offer insight on the Reynolds number sensitivities of the various data. Moreover both the Mexico experiment as well as the NASA-Ames experiment have also been done on smaller scales which leads to insights on scaling effects. In Mexnext-III this task will run at a slower pace.

Task 4.3: Angle of attack
For many aerodynamic investigations, the angle of attack is a crucial quantity. However the definition, determination and measurement of the angle of attack for a rotating wind turbine is far from straightforward. Several investigations on the angle of attack will be performed.

Task 4.4: Near wake aerodynamics, including tip vortex trajectories and the turbulent wake state
Several measurements are available with detailed information on the flow field at the near wake.

Task 4.5: Non-uniformity of flow between the blades
In this task the non-uniformity of the flow between the blades will be studied, explained and evaluated with common theory.

The task makes use of flow field measurements carried out in the rotor  plane. Then the effects of non-uniformity of the flow in the tip region are analyses, which is usually corrected for by Prandtl’s tip correction model in Blade Element Momentum (BEM) methods.

Task 4.6: 3D effects
In this task the 3D effects on the rotating airfoil data are being analysed. Sectional data as measured on the 3D blade are compared with 2D airfoil data in order to distinguish the rotational effects on the airfoil data. A comparison with standstill data will also be made.

Task 4.7: Yawed flow and instationary airfoil aerodynamics
This task focusses on the load and velocity variations due to yaw. these variations may be accompanied by instationary effects on the airfoil aerodynamics.

Task 4.8: Dynamic Inflow
Dynamic inflow is related to the unsteady effect on the induction at e.g. pitching steps. Several measurements at such conditions have been taken and will be analysed.

Task 4.9: Boundary layer transition
Some experiments have performed dedicated experiments on boundary layer transition. The transition location from these rotating measurements will  be compared  with the location from 2D wind tunnel measurements and with calculations. (New) Mexico measurements with the fast Kulite transducers may also help in the detection of transition.

Task 4.10: Acoustics
In New Mexico an acoustic array was placed next to the turbine. Acoustic data  have been taken in parallel to aerodynamic data which will facilitate in determining the aerodynamic-acoustic link 

Task 4.11: Devices
In New Mexico measurements have been taken with flow devices on the blade (e.g. Guerney flaps and root spoilers). These measurements will be analysed.

Task 4.12: IEC aerodynamics
In New Mexico measurements have been taken at large pitch misalignments, i.e. an important IEC load case. It was decided to combine the activities in this task with those of task 4.1 (stand still aerodynamics)

It is noted that Mexnext-I and II are finished. Mexnext-III runs from January 1st 2015 until December 31st 2017.