  Human factors, specifically visual impact and noise production, are the
current main limitations for broader urban wind energy exploitation. Trailing
edge noise, caused by the turbulent boundary layer interacting with the airfoil
surface, is the primary source of noise of modern horizontal and vertical axis
wind turbines. Low inflow turbulence levels do not affect the trailing edge
noise. However, an inflow of high turbulence intensity has flow structures that
can penetrate the boundary layer, increasing the velocity fluctuations inside
the boundary layer and, consequently, the wall pressure fluctuations and
trailing edge noise. This research investigates the effect of high free-stream
turbulence, observed in the atmospheric boundary layer of urban zones, in the
trailing edge noise generation. This was performed by measuring the increment
of the turbulence inside of the boundary layer and surface pressure
fluctuations near the trailing edge when an airfoil is submitted to high inflow
turbulence. Experimental measurements were performed in the Aeroacoustic Wind
Tunnel of the University of Twente on a NACA 0012 airfoil subjected to a
turbulent inflow. The chord-based Reynolds number of the experiments ranged
from 170 x 10^3 to 500 x 10^3. Results showed that high inflow turbulence
significantly increases the velocity fluctuations and the integral length scale
along the entire boundary layer, resulting in an increment of the surface
pressure spectrum more than 6 dB and 10 dB in the entire frequency range for
10% and 20% of free-stream turbulence, respectively. The 10% free-stream
turbulence increases the velocity fluctuations just in the low--frequency
range, whereas the 20% inflow turbulence influences the velocity spectrum in
the entire frequency range, increasing the size of the smallest structures of
the turbulence. Amiet's theory is applied to predict the trailing edge
far-field noise.
