Introduction to quiz: Wind data analysis This document contains all the information you need to solve the quiz called 'Wind profiles and wind resources'. Please calculate your answers to the questions at the bottom of this page. You will then be prepared to start the quiz. We recommend using a calculation tool such as a spread sheet or a computer programming tool to solve the exercise. You can download this document in PDF format:
Learning Objectives When you have completed this exercise, you will be able to: Determine the mean wind speed and turbulence from measured wind data Explain what the quantities 'turbulence scales' and 'integral time scales' mean physically
Description Wind data is obtained from the measurements of a sonic anemometer mounted on a 116.5m tall meteorological mast, located at Danish National Test Center for Large Wind Turbines at Høvsøre, Denmark. F igure 1. shows the location of the test center (see inset). The site is about 1.7km from the North Sea with a mean height of 2m above mean sea level and flat homogeneous terrain. The site also comprises five turbine stands, five power curve masts, two lighting towers and a central service building.
Data A PDF data file contains 20H z measurements of the u, v and w components using a sonic anemometer over a 30 min period. MOOCTurbulenceExercise.pdf (https://d3c33hcgiwev3.cloudfront.net/… The same data is available in .txt format. MOOCTurbulenceDataSeriesexel.txt (https://d3c33hcgiwev3.cloudfro… The same data is available in Excel format. MOOCTurbulenceDataSeries.xls (https://d3c33hcgiwev3.cloudfront.n…
Questions Please use the data set given above to complete the following tasks. Write down your answers as you go. You will need them when you answer the quiz. 1. Separate the time series into mean and fluctuating parts. Plot the time series of the fluctuating parts of each component. For which component does the variations in wind speed look larger? 2. Compute the mean of each component. Is the mean of v and w approximately zero? If yes, why? 3. Compute the standard deviation of each component. Which of the components (u, v, w) has the largest standard deviation? 4. The figure below shows turbulence spectra of the u, v , and w components. Which turbulence scales are larger and why? Hint: Refer to the video lecture for the definition of turbulence scales based on the spectra.
5. The figure below shows the auto-correlation function of the u component. The integral time scale is computed from the definition (see video lecture), where the integration is performed up to the time lag where the autocorrelation function crosses zero the first time. Its value turns out to be approximately 116 seconds. What does the integral time scale mean physically?
Summary Through this exercise, you have learnt: To estimate sample statistics How the spectra of different wind field components look as well as their respective characteristic scales How the measured sample auto-correlation function looks and what the physical meaning of the integral scale is.
