@book{348cad19f19d4500934c7b653712b85f,

title = "Determining the Velocity Fine Structure by a Laser Anemometer in VAD operation",

abstract = "The theoretical basis for determining the dissipation ε, by measuring the velocity structure function with a CW-laser anemometer has been derived in the case of calm wind conditions. If there is a well defined mean wind speed the structure function can be obtained by having the laser beam pointing in one direction and measure a time series of the Doppler wind velocity component along the beam. Applying Taylor{\textquoteright}s hypothesis the structure function can be calculated. This technique was discussed by Kristensen et al. (2011). Taylor{\textquoteright}s hypothesis cannot, however, be used if there is no mean wind.Then it is necessary to “create” a mean wind by turning the laser beam. Since the instrument is not moved the beam will describe a cone which could be a VAD-scanning. In any case the measured velocity components will not be parallel and this implies that the measured structure function will contain a term which is proportional to the total variance. The theoretical expression for the line-filtered structure function is derived in two equivalent ways, one in physical space and one in wave-number space, of which the last can be reliably evaluated by numerical integration. Also a practical approximate equation, derived in the physical space, is presented.",

keywords = "DTU-Wind-Energy-E-0008(EN)",

author = "Leif Kristensen and Peter Kirkegaard and Torben Mikkelsen",

year = "2012",

language = "English",

series = "DTU Wind Energy E",

number = "0008",

publisher = "DTU Wind Energy",

address = "Denmark",

}