PDF《wind direction changes (EOD)》

Full scale experimental analysis of extreme coherent gust with wind direction changes (EOD) K S Hansen1 and G C Larsen2

1 Department of Mechanical Engineering, Fluid Mechanics, Nils Koppels Allé, DTU- Building 403, Technical University of Denmark, DK-2800 Lyngby;

Phone: +45

4525 4318

2 Wind Energy Department, Ris? National Laboratories, Technical University of Denmark, P.

O. Box 49, DK-4000 Roskilde;

Phone: +45

4677 5056 E-mail: [email protected] Abstract. A coherent wind speed and wind direction change (ECD) load case is defined in the wind turbine standard. This load case is an essential extreme load case that e.g. may be design driving for flap defection of active stall controlled wind turbines. The present analysis identifies statistically the magnitudes of a joint gust event defined by a simultaneously wind speed- and direction change in order to obtain an indication of the validity of the magnitudes specified in the IEC code. The analysis relates to pre-specified recurrence periods and is based on full-scale wind field measurements. The wind speed gust amplitude, occurring simultaneously with a wind direction change, corresponds well to the recommended ECD value of

15 m/s, except for the complex terrain case, where estimated extreme wind speed gust amplitudes are seen to exceed the IEC value with approximately 50%. The estimated extreme wind direction gust amplitudes associated with the investigated European sites are low compared to the recommended IEC- values. However, these values, as function of the mean wind speed, are difficult to validate thoroughly due to the limited number of fully correlated measurements. 1. Introduction A coherent wind speed and wind direction change (ECD) load case is defined in the IEC 64100-1 standard [1]. This load case is an essential extreme load case that e.g. may be design driving for flap defection of active stall controlled wind turbines. The purpose of the present analysis is to identify statistically the magnitudes of a joint gust event defined by a simultaneously wind speed- and direction change in order to obtain an indication of the validity of the magnitudes specified in the IEC code. The analysis relates to pre-specified recurrence periods and is based on full-scale wind field measurements. 2. Nomenclature ECD Extreme Coherent GDI Gust Directional Index;

defined in equation (1) U(t) Horizontal Wind Speed time series;

sampled with frequency ≥

1 Hz Dir(t) Horizontal Wind Direction time series;

sampled with frequency ≥

1 Hz PDF Probability Density Function Δt Gust rise time in (=10) seconds Vcg Wind speed gust amplitude (m/s) Vhub 10-minute average wind speed at hub height (m/s) Dircg Wind direction gust amplitude (?) α,β Parameters defining the EV1 distribution Ta Apparent basic return period P50cg

50 year quantile Nt Total number of populations Nc Number of fully correlated events 3. Definitions Determination of extreme ECD magnitudes requires a large amount of measured time series due to the limited occurrence of such gust events. A suitable collection of data for this analysis is available from Database on Wind Characteristics [2], [3], [4], where a huge amount of simultaneously recorded full-scale wind speed and wind direction measurement time series is stored. These time series are indexed in terms of mean statistics, maximum gust sizes and various kinds of derived statistics, which enables a direct identification of ECD situations in the measured data. The index parameter relevant for the ECD event is the Gust Directional Index (GDI) parameter, which is defined in equation (1) (1) where, at a given position, U(t) is the measured wind speed, and Dir(t) is the simultaneous measured wind direction. For a given time series, the maximum value of the GDI index is in the range [1;