  The meteorological conditions markedly affect the energy efficiencies and
cost/power rate of the wind turbines. This study numerically investigates the
performance of the National Renewable Energy Laboratory (NREL) Phase VI wind
turbine, designed to be insusceptible to surface roughness, undergoing either
clean or dusty air. First, the numerical approach is validated against the
available experimental data for clean air. Following this, the model is
developed into a Lagrangian-Eulerian multiphase approach to comprehensively
analyze the effects of the dusty air. The dependence of aerodynamic performance
on the wind speed (= 5-25 m/s), particle diameter dp (= 0.025-0.9 mm) and angle
of attack (= 0o-44o) is investigated. It is found that the turbine performance
generally deteriorates in dusty conditions. But it becomes relatively acute for
dp > 0.1 mm and post-stall state. As such, the generated power is reduced by
4.3% and 13.3% on average for the air with the dp = 0.05 and 0.9 mm,
respectively. The particles change the flow field profoundly, declining the
pressure difference between the suction/pressure sides of the blade-airfoil,
advancing the boundary layer separation, and strengthening the recirculation
zones. The above changes account for a lower lift coefficient and higher drag
coefficient.
