1 / 36

Turbulence measurements using lidars

Turbulence measurements using lidars. Ameya Sathe and Jakob Mann. What do we mean by turbulence ?. Outline. How lidars measure turbulence? Can lidars measure turbulence? How can lidars measure turbulence?. Part I How lidars measure turbulence?. Basic principles of measurement.

finola
Download Presentation

Turbulence measurements using lidars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Turbulence measurements using lidars Ameya Sathe and Jakob Mann

  2. What do wemean by turbulence?

  3. Outline • How lidars measure turbulence? • Can lidars measure turbulence? • How can lidars measure turbulence?

  4. Part IHow lidars measure turbulence?

  5. Basic principles of measurement

  6. How are the wind speeds retrieved? • ZephIR • Windcube

  7. Lidarvs true turbulence measurement • True turbulence • Lidar turbulence 3D spectral velocity tensor • For detailed derivation

  8. Lidar turbulence derivation

  9. Generic Expression for Lidar turbulence

  10. Lidarvs true turbulence measurement • True turbulence • Lidarturbulence –> m=1,n=1, i.e. u variance

  11. ClickerQuestion – What problems do/doeslidarmeasuredturbulence have using VAD scanning? • No problems, measuresturbulencewell • Averaging of turbulence • Contribution of othercomponents of Reynolds stress tensor • B and C

  12. ClickerQuestion – Say, we have a perfectlidarthatmeasures at a point. What problems willthislidar have whilemeasuringturbulenceusing VAD scanning? • No problems, measuresturbulencewell • Averaging of turbulence • Contribution of othercomponents of Reynolds stress tensor • B and C

  13. TurbulenceSpectra definitions True autocovariancefunction

  14. Turbulencespectrameasured by lidars Lidarmeasuredautocovariancefunction Separation distance for the u-component • For detailed derivation

  15. Part IICan lidars measure turbulence?

  16. Comparison of the model and measurements – CW lidar Ideal case Model Measurements Neutral conditions

  17. Comparison of the model and measurements – CW lidar Ideal case Ideal case Model Model Measurements Measurements Stable conditions Unstable conditions

  18. Comparison of the model and measurements – Pulsed lidar Neutral conditions

  19. Comparison of the model and measurements – Pulsed lidar Stable conditions Unstable conditions

  20. Comparison of the model and measurements – Pulsed lidar, u-spectra Lidar Lidar Sonic Sonic 60 m 100 m

  21. Comparison of the model and measurements – Pulsed lidar, v-spectra Lidar Lidar Sonic Sonic 60 m 100 m

  22. Comparison of the model and measurements – Pulsed lidar, w-spectra Lidar Lidar Sonic Sonic 60 m 100 m

  23. ClickerQuestion – Canweretrieve true turbulence from the ratio • Yes • No • May be

  24. Part IIIHow can lidars measure turbulence?

  25. Basic Principles Recall !! In principle, only 6 beams are required to measure Reynolds stress tensor

  26. Optimum 6-beam configuration? We optimize this configuration to minimize the random errors in the measurement of Reynolds stress tensor • For details

  27. Why only a specific configuration?

  28. Why only a specific configuration?

  29. Optimizing the configuration

  30. Comparing the 6 beam configuration with the conical scanning method – CW lidar VAD scanning 6-beam Ideal case Neutral conditions

  31. Comparing the 6 beam configuration with the conical scanning method – CW lidar Ideal case Ideal case Unstable conditions Stable conditions

  32. Comparing the 6 beam configuration with the conical scanning method – Pulsed lidar Conical scanning 6-beam Ideal case Neutral conditions

  33. Comparing the 6 beam configuration with the conical scanning method – Pulsed lidar Ideal case Ideal case Unstable conditions Stable conditions

  34. Summary • Howlidarsmeasure the Reynolds stress tensor under VAD scanning • Howlidarsmeasureturbulencespectra under VAD scanning • Twomechanismsareresponsible for large systematicerrorsusing VAD scanning: • Averaging in the probevolume • Contamination by othercomponents of the Reynolds stress tensor • If wewant to measureturbulence as per the standard definitions then VAD scanning should not beused • Sixbeammethoddoes not contaminateturbulencemeasurements, but averaging problem still remains Future work • 6-beam experiment planned at DTU Wind Energy, Risø Campus (but could be conducted elsewhere too!!) • Further data analysis to get rid of volume averaging

  35. ClickerQuestion – Is turbulencemeasuredusing the VAD scanning only a problem for lidars? • Yes, Onlylidarswill have problems • No, lidars and sodarswill have problems • No, Any instrument performing VAD scanning will have problems

  36. Thank youContact: amsat@dtu.dk

More Related