bReeze (version 0.3-2)

turbulence: Calculation of turbulence intensity

Description

Calculates turbulence intensity and mean wind speed for each given direction sector.

Usage

turbulence(mast, turb.set, dir.set, num.sectors=12, 
  bins=c(5, 10, 15, 20), subset, digits=3, print=TRUE)
turb(mast, turb.set, dir.set, num.sectors=12, 
  bins=c(5, 10, 15, 20), subset, digits=3, print=TRUE)

Arguments

mast

Met mast object created by createMast.

turb.set

Set used for turbulence intensity, specified as set number or set name (optional, if dir.set is given).

dir.set

Set used for wind direction, specified as set number or set name (optional, if turb.set is given).

num.sectors

Number of wind direction sectors as integer value greater 1. Default is 12.

bins

Wind speed bins as numeric vector or NULL if no classification is desired.

subset

Optional start and end time stamp for a data subset, as string vector c(start, end). The time stamps format shall follow the rules of ISO 8601 international standard, e.g. "2012-08-08 22:55:00".

digits

Number of decimal places to be used for results as numeric value. Default is 3.

print

If TRUE, results are printed directly.

Value

• Returns a data frame containing:
• wind.speed
  Mean wind speed for each direction sector.
• total
  Total turbulence intensity for each direction sector.
• ...
  Turbulence intensities per direction sector for each given wind speed bin.

encoding

UTF-8

Details

Turbulence can be perceived as wind speed fluctuations on a relatively short time scale and it strongly depends on surface roughness, terrain features, as well as thermal effects. High turbulence should be avoided, since it is a main driver of fatigue loads and might decrease energy output. A measure of the overall level of turbulence, is the turbulence intensity $I$, which is defined as: $$I = \frac{\sigma}{\bar v}$$ where $\sigma$ is the standard deviation of wind speed -- usually measured over a 10-minutes period -- and $\bar v$ is the mean wind speed over this period.

References

Albers, A. (2010) Turbulence and Shear Normalisation of Wind Turbine Power Curve. Proceedings of the EWEC 2010, Warsaw, Poland

Burton, T., Sharpe, D., Jenkins, N., Bossanyi, E. (2001) Wind Energy Handbook. New York: Wiley

Langreder, W. (2010) Wind Resource and Site Assessment. In: Wei Tong (Ed.), Wind Power Generation and Wind Turbine Design, Chapter 2, p. 49--87, Southampton: WIT Press

See Also

createMast, plotTurbulence, printObject

Examples

# load and prepare data
data(winddata)
set40 <- createSet(height=40, v.avg=winddata[,2], v.std=winddata[,5],
  dir.avg=winddata[,14])
set30 <- createSet(height=30, v.avg=winddata[,6], v.std=winddata[,9],
  dir.avg=winddata[,16])
set20 <- createSet(height=20, v.avg=winddata[,10], v.std=winddata[,13])
ts <- formatTS(time.stamp=winddata[,1])
neubuerg <- createMast(time.stamp=ts, set40, set30, set20)
neubuerg <- clean(mast=neubuerg)

# calculate turbulence intensity
turbulence(mast=neubuerg, turb.set=1)

# use different datasets for turb.set and dir.set
turbulence(mast=neubuerg, turb.set=1, dir.set=2)
turbulence(mast=neubuerg, turb.set="set1", dir.set="set2")	# same as above

# change number of direction sectors
turbulence(mast=neubuerg, turb.set=1, num.sectors=4)

# calculate turbulence intensity for 1 m/s speed bins and without binning
turbulence(mast=neubuerg, turb.set=1, bins=1:25)
turbulence(mast=neubuerg, turb.set=1, bins=NULL)

# data subset
turbulence(mast=neubuerg, turb.set=1, 
  subset=c(NA, "2010-01-01 00:00:00"))

# change number of digits and hide results
turbulence(mast=neubuerg, turb.set=1, digits=2)
turbulence(mast=neubuerg, turb.set=1, print=FALSE)