Abstract. Leading-edge inflatable (LEI) kites are characterized
by a pronounced downward curvature of the wing and flow recirculation
zones on the pressure side. This study presents novel stereoscopic
particle image velocimetry (PIV) measurements of a 1:6.5 rigid scale
model of the TU Delft V3 LEI kite. The flow-field measurements were
conducted in the Open Jet Facility of Delft University of Technology for
two angles of attack and seven chordwise measurement planes positioned
between mid-span and tip, and were compared with results from
Reynolds-averaged Navier–Stokes (RANS) simulations. The double-curved
anhedral wing geometry presented several challenges, such as surface
reflections that required careful data processing and the use of a
lateral velocity filter. The circulation distribution was analyzed,
using both elliptical and rectangular boundary curves, showing good
agreement in trends between the vortex-step method (VSM), RANS, and PIV
data. The lift and drag coefficients of each chordwise measurement plane
were estimated using the Kutta–Joukowski theorem, surface pressure
integration of RANS CFD data, and Noca’s method – an inherently
three-dimensional reformulation of the momentum conservation equations
expressed solely as surface integrals over the control-volume boundary –
applied here in two dimensions. While the mid-span to tip variation of
lift coefficients was in accordance with the anhedral shape and
tip-vortex effects, the drag measurements and predictions deviated from
the expected behavior by exhibiting negative values. Especially near the
tip region, significant discrepancies were observed, attributed to
increased measurement uncertainty. The surface pressure integration
revealed discrepancies at the strut junction, likely due to local
three-dimensional strut-induced flow effects and increased airfoil
thickness. This study provides comprehensive validation data for CFD
simulations of LEI kites while highlighting the challenges in PIV
measurements of double-curved anhedral wings and characterizing local
aerodynamic phenomena.
https://doi.org/10.5281/zenodo.4059767