An experimental study of the unsteady aerodynamics of a DU91-W2-150
airfoil at large angles of attack
Abstract
The airfoil DU91-W2-150 was investigated in the Low Speed Low Turbulence
Tunnel at the Delft University of Technology to study unsteady
aerodynamics. This experimental study tested the airfoil under a wide
range of angles of attack (AoA) from 0 ◦ to 3 1 0 ◦ at three Reynolds
numbers ( Re) from 2 × 1 0 5 to 8 × 1 0 5 . Pressure on the
airfoil surface was measured and Particle Image Velocimetry (PIV)
measurements were conducted to capture the flow field in the wake. By
examining the force coefficient and comparing the wake contours, it
shows that an upwind concave surface provides a higher load compared to
a convex surface upwind case, highlighting the critical role of surface
shape in aerodynamics. When comparing separation at specific locations
along the chord for all three Res, it is observed that as
Re increases, separation tends to occur at lower angles of
attack, both for positive stall and negative stall. The examination of
the aerodynamic force variation indicates that, during reverse flow,
fluctuations are more pronounced compared to forward flow. This is owing
to separation occurring at the aerodynamic leading edge (geometric
trailing edge) in reverse flow. In terms of vortex shedding frequency,
the study found a nearly constant normalized Strouhal number (
St) of 0.16 across various Res and AoAs in fully separated
regions, indicating a consistent pattern under these conditions.
However, a slight increase in St, between 0.16 and 0.20, was
observed for AoAs exceeding 180 degrees, possibly due to the convex
curvature of the airfoil in the upwind direction. In conclusion, this
research not only corroborates previous findings for small AoAs, but
also adds new data on the aerodynamic behavior of the DU91-W2-150
airfoil under large AoAs, offering various perspectives on the effects
of surface curvature, Re, and flow conditions on key aerodynamic
parameters.