Wind turbine noise is known to have special property, very easily detectable and cause annoyance at relatively lower sound level. Previous studies assumed that amplitude modulation might be main factor of the property of wind turbine noise. The studies also said that knowledge of relationship between amplitude modulation and detection threshold can be helpful for reducing the effect of wind turbine noise by using auditory masking. So, the aim of this study is to investigate whether the amplitude modulation is really main cause of high detectability of wind turbine noise or not. And if so, we also wanted to find out how much the detection threshold can be lowered according to a modulation depth. In order to test this, an experiment was conducted using threshold tracking method. Twelve participants determined the detection thresholds of five target sounds in presence of masker sounds. The results showed that detection threshold is lowered as the modulation depth is increased. For reliability, the results were compared with predictions from Glasberg and Moore's model. Modified method of determining detection thresholds is suggested to complement differences between test results and predictions. For effectiveness, the way of determining detection thresholds by using A-weighed maximum sound level is also discussed.

The downstream velocity of the NREL phsase VI blade was measured by using the 5 hole probe in KARI low speed wind tunnel. The test was designed to study the scale down effect on the wind turbine blade in wind tunnel test. The downstream flow could be used as an indicator for the aerodynamic stall phenomena of the blade. A measurement campaign for the downstream flow on the nominal condition and stall condition was conducted in wind tunnel test. The relation between downstream flow and induction factor was derived on the consumption of far boundary condition. X=2.0R position was selected as a far boundary position and the measurement result was compared with the BEMT analysis results. The comparison result shows that downstream measurement well agreed with the BEMT analysis.