Chapter 5: VAWT wind tunnel experiments

Experimental testing is an essential part of the wind turbine design path, as it provides early information about aerodynamics, mechanics, performance, and turbine control. According to the size and the budget or the certification purposes, the testing environment can be either natural through field testing, or controlled in dedicated facilities called wind tunnels. The testing procedure provides time series of measured data at a given sampling rate, that needs proper data post-processing for a rational use. Following the stochastic nature of wind, the data treatment needs always statistical tools and appropriate uncertainty analysis. The advantage of infield measurements is to perform full-scale tests, from which the real turbine behavior can be simulated and evaluated. The site has to be certified according to Annex A of IEC 61400-12-1, 2005. A few sites have the characteristics suited to host wind turbine test campaigns, and depending on the windiness of the location from 1-2 years can be necessary to complete the measurements. On the other hand, wind tunnel tests can only be performed on scaled prototypes, with some dimensional limitations compared to real size turbines. The controlled environment conditions allows repeatable tests and to separate some effects that in open field tests are often superimposed and and difficult to disaggregate. In particular, the calibration and validation of numerical codes can be made through controlled experiments. From the point of view of the market oriented wind turbine development, wind tunnel tests can represent the very early stage of a more wide experimental campaign, followed by infield tests.