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Delegates are invited to meet and discuss with the poster presenters during the poster presentation sessions between 10:30-11:30 and 16:00-17:00 on Thursday, 19 November 2015.

Lead Session Chair:
Stephan Barth, ForWind - Center for Wind Energy Research, Germany
Alfonso Ruiz Acciona Windpower, S.A., Spain
Co-authors:
Alfonso Ruiz (1) F
(1) Acciona Windpower, S.A., Sarriguren, Spain

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2015 and are published here unedited

Alfonso Ruiz is a mechanical Engineer with more than 15 years of experience in R&D management in several sectors. As an R+D+i Management System expert, he has dealt with the following issues: Creativity, Technology Surveillance and R&D projects management.
In 2011 he joined Acciona Windpower as a Senior R&D engineer, more specifically within the Research and Patents area, holding tasks as Intellectual Property expert in the wind industry and involved in several research projects dealing mainly with power curve improvements and measurement techniques and drive train analysis.
He is the co-inventor of 9 patent applications, 6 related to wind turbines.


Poster

Poster Download poster (11.46 MB)

Abstract

Influence of Upflow on Nacelle Power Curves

Introduction

Nacelle Power Curves (NPC) are increasingly being used for wind turbine performance evaluation.

NPC is a powerful tool for wind farm monitoring and maintenance operations. Nevertheless, NPCs are affected by most of the uncertainties and effects that distort standard Power Curves (PC) obtained according to IEC 61400-12-1 and also by local wind flow effects related to anemometry equipment location. Those may further disturb the results and therefore the conclusions based on this type of analysis.

Nacelle anemometry equipment in the WT is subjected to flow distortion due to blades rotation. This is a well-known effect, and is compensated, under certain conditions, by the Nacelle Transfer Function.

But also the position of the anemometer on the nacelle cover makes the wind speed measurements sensitive to inflow angle (or upflow) due to the flow distortion produced by the hub and nacelle cover.

This work analyzes how upflow affect NPC and how this effect can be quantified and accounted for.

Approach

To quantify the effect of inflow angle on NPCs, a ground-based LiDAR has been used. This equipment has been installed in an experimental windfarm for monitoring an AW116/3000 wind turbine.

LiDAR allows upflow and other wind parameters measurements at different heights, being possible to measure wind properties up to upper blade-tip height.

The ratio hub-height free wind speed / nacelle anemometer wind speed is analyzed for different upflow values.

The LiDAR is also used to characterize the inflow at the site and determine the influence of several factors in the upflow values.

Main body of abstract

Results of the test campaign show that the ratio hub-height free wind speed / nacelle anemometer wind speed increases with increasing upflow values.

This is due to the shadow effect of the nacelle cover in the nacelle anemometer that causes lower wind speed measurements than those measured by the LiDAR at hub height.

In order to get a more accurate NPC, correction coefficients have been calculated to account for the effect of inflow angle. These coefficients depend on the inflow angle and are applied to the nacelle wind speed measurements after application of the NTF.

When upflow measurements are not available, estimations based on the site resource assessment may be used. These estimations give only inflow angle average values for each wind direction sector, although this study reveals that it depends heavily on other factors.

Data from the LiDAR has also been used to characterize inflow angle at the site. This analysis reveals dependency of inflow angles with:
- Height: higher upflow values at lower heights
- Wind direction: very dependent of orography
- Wind speed: higher upflow values with lower wind speeds
- Day/Night: slightly higher values during the day (probably due to sun radiation)
- Season

All these influences should be taken into account when estimating the inflow angle values at the WT site. So rather than using a constant value for each wind sector, a finer estimation is made based on hub height, wind speed, season and time of the day.

Distortion in wind direction measurement due to upflow is also analyzed.

Conclusion

Due to its position on the nacelle cover, nacelle anemometry measurements are affected by inflow angle. This distortion affects analysis based on NPC and therefore must be accounted for and if possible compensated.

Besides, inflow angle values are dependent also on several factors such as wind speed, wind direction and height. This influence can be quantified and used to better estimate upflow values according to current conditions in order to even better correct nacelle anemometry measurements.


Learning objectives
Understand how inflow angle affects wind measurements by nacelle anemometry.

Quantify the influence of several factors on the inflow angle.

Estimate upflow values based on current conditions.

Compensate wind measurements based on upflow measurements or estimations in order to obtain a more precise NPC.