The Inverse Vortex Wake Model: A Measurement Analysis Tool

Abstract

To reduce the level of uncertainty associated with current rotor aerodynamics codes, improved understanding of rotor aerodynamics is required. Wind tunnel measurements on model rotors contribute to advancing our knowledge on rotor aerodynamics. The combined recording of blade loads and rotor wake is desired, because of the coupled blade and wake aerodynamics. In general, however, the small size of model rotors prohibits detailed blade load measurements; only the rotor wake is recorded. To estimate the experimental blade flow conditions, a measurement analysis tool is developed: the inverse vortex wake model. The rotor wake is approximated by a lifting line model, using rotor wake measurements to reconstruct the vortex wake. Conservation of circulation, combined with the Biot–Savart law, allows the induced velocity to be expressed in terms of the bound circulation. The unknown bound circulation can be solved for, since the velocity is known from rotor wake measurements. The inverse vortex wake model is subsequently applied to measurements on the near wake of a model rotor subject to both axial and yawed flow conditions, performed at a TUDelft open jet wind tunnel. The inverse vortex wake model estimates the unsteady experimental blade flow conditions and loads that otherwise would have remained obscured.

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

“…Wind Energ. Sci., 1, 89-100, 2016 www.wind-energ-sci.net/1/89/2016/ The fact that γ chordwise is distributed over such a large area of the root might explain that the root vortex does not present a well-defined, distinctive structure, as Vermeer et al (2003), Massouh and Dobrev (2007), and Haans et al (2008) reported in their experimental wake studies of different wind turbines. Furthermore, the existence of two adjacent root regions with counter-rotating γ chordwise might also explain the fast diffusion of the root vortex reported by Ebert and Wood (2001) and Sherry et al (2013).…”

“…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.…”

Experimentally observed effects of yaw misalignment on the inflow in the rotor plane

“…The inverse vortex wake model of Haans et al [16] is numerically discretized in order to increase its flexibility and computational efficiency. Furthermore, its capabilities are extended to yawed flow conditions.…”

“…The current paper presents an updated version of the inverse vortex wake method discussed in [16]. Furthermore, blade loads and inflow conditions at the rotor plane are discussed that result from application of the analysis tool to near-wake measurements on a model rotor subject to yawed flow conditions.…”

“…Both the concept and the construction of the first version of the inverse vortex wake model are discussed by Haans et. al [16]. At present, a summary of the model concept is given in Section 3.1, since the model concept for the updated version, discussed in this paper, is equal to that of the first version.…”