johng Posted June 27, 2008 Report Share Posted June 27, 2008 Hello,What are good applications for the new 95" boom? Iwas thinking about using it on a standard 60-m tower instead of the 60"boom. Looking at a tower shadow sketch, I see that getting a sensoronly four tower diameters away from the tower would give a reading ofat worst +/- 2% of free stream. For a 10" tube, that's only 40", andthe standard boom is 60". So even if I were trying to getvery clean readings at 10m AGL (on the 10" part of the tower), the 60"boom would be fine for every circumstance except for when the sensor isdirectly downwind (when you're screwed no matter what). Best regards,Alex DePillis --- The short answer is that the new 95 inch boom can be used in applicationswhich require lower measurement uncertainty than the 60 inch boom. As for the long answer... I believe you might be looking at Figure G.5 in IEC 61400-12-1 which isbased on 2 dimensional Navier-Stokes computations. If so, the figures you indicate are about right (4 tower diameters equatesto about a 2.3% centerline disturbance). Another consideration is that the IEC model measures the offset distanceas tower centerline to sensor centerline, which really places the 60 inch boomat about 6.5 diameters (for a 10 inch tower) equating to a centerlinedisturbance of about 1%. However, here is another way to look at it...what level of disturbance isacceptable for your wind resource assessment campaign? Many in the industry would say "let?s make it 0.00%!"... Basically, the further the sensor is away from the tower, the lower thedisturbance. In reality, the law ofdiminishing returns comes into play and no matter how long a boom is(realistically) the disturbance will not (in theory) be 0.00%. At about10 diameters, the disturbance curve flattens out and approacheshorizontal. This is really the sweet spot of boom design as thecenterline disturbance is less than 0.5% (some might say it is about 0.3% but Iprefer to be a bit conservative). I havealso heard that some in the industry believe disturbances are actually greaterthan what the Navier-Stokes model predicts. If anyone has seen research papers in this area, please add links tothis thread! Of course, other design factors are involved such as robustness, cost, easeof installation and transport (the new booms are cost effective, easy toinstall and are also UPS shippable). In summary, NRG will continue to offer both the 60 inch boom and the 95 inchboom. The new 95 inch boom can be used in applicationswhich require lower measurement uncertainty than the 60 inch boom. Link to comment Share on other sites More sharing options...
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