Boundary layer transition over a lowreynolds number rotor : effects of roughness and freestream turbulence
Résumé
Two separate experiments are conducted on a three
bladed NACA0012 rotor operating at low Reynolds numbers
using phase-locked infrared thermography coupled
with simultaneous force and torque measurements. The
first, focuses on the effects of freestream turbulence
on boundary layer transition over the suction side of
the aerofoil of the rotor in an advancing configuration.
Freestream turbulence (FST) was generated in an open
section wind tunnel using grids and was characterized using
Hot-Wire anemometry. In general, when the rotor
was subjected to FST, an increase in thrust and efficiency
was observed, which could be due to the FST suppressing
flow separation or by inducing early transition. The second
experiment, consisted of a parametric study on the
impact of forcing boundary layer transition using roughness
placed on the suction side of the aerofoil, in a hover
configuration. The height of the roughness was varied
from 52-220μm and was placed at all at at 10% chord,
over the entire span of the blade. Force and torque measurements revealed that there could be a optimal roughness height that could lead to a performance increase.
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