Exploration of the vortex wake behind of wind turbine rotor

Detailed analysis of the blade root flow of a horizontal axis wind turbine

“…Many wind tunnel experiments with model wind turbines confirmed this. For instance, Massouh and Dobrev (2007) and Haans et al (2008) also came to that conclusion after studying a wind turbine rotor wake with particle image velocimetry (PIV) and hot film wake measurements, respectively. Furthermore, Ebert and Wood (2001) and Sherry et al (2013) observed by means of PIV (among other measurement techniques) that the root vortex diffuses very rapidly.…”

“…On the other hand, the local blade solidity c/r, which has also been identified as a fundamental parameter for the Himmelskamp effect (see, e.g., Snel et al, 1993;Chaviaropoulos and Hansen, 2000;Lindenburg, 2003;Dowler and Schmitz, 2015), differs substantially between the TU-Delft and the NREL 5 MW turbines: at r = 0.26R (i.e. the radial position studied in Figs.…”

“…Centrifugal force: the centrifugal force that acts on the bottom of the boundary layer (i.e. the region where the flow is not detached from the surface) pushes the flow towards the tip (Du and Selig, 1999;Lindenburg, 2003;Guntur and Sørensen, 2014).…”

“…This is important because it contributes to maintain the same balance between the centrifugal and Coriolis forces, which is fundamental for the Himmelskamp effect. Lindenburg (2003), for instance, estimated that the change of aerodynamic lift and drag due to the Himmelskamp effect is proportional to the square of the local speed ratio ωr/U rel . Dowler and Schmitz (2015) also included a similar parameter, namely 2U rel /ωr (obtained directly from the ratio between the Coriolis and centrifugal forces) in their stall delay model.…”

Natural snowfall reveals large-scale flow structures in the wake of a 2.5-MW wind turbine

“…Particle image velocimetery (PIV), based on tracking the displacement of tracers in an illuminated flow field 10,11 , is the only measurement technique capable of obtaining planar velocity distributions with the spatio-temporal resolution required to study flow-structure interactions. However, PIV has only been applied, so far, to small-scale turbine models, from 0.1 m to a few metres in wind tunnel experiments [12][13][14][15][16][17] . One of the main obstacles to PIV implementation on a utility-scale turbine is the requirement to seed a large flow field (B100 m) with tracers uniformly and persistently distributed, in an environmentally benign, economic and non-intrusive fashion, which makes it almost impossible to use artificial seeding methods.…”