| Abstrakt: |
The aim of this work is to study the influence of the blade shape and curvature changing of characteristics of the helicopter's rotational noise. To this end, we consider 4-digits NASA profiles whose rotational noise is compared with one of the parabolic blade. Calculations results show that 4-digits blade generated rotational noise of higher level and its distribution on the blade's shape are smooth in comparison with noise distribution of parabolic blade. However, the parabolic blade has more expressive maximum of noise level than the 4-digits blade. It can be explained by the difference of low-frequency spectrum generated by parabolic blade. We determine that the maximum of the rotational noise L (with respect to 2 · 10-5 Pa) was at the distance of 0,7-0,75 blade radius. This agrees with Gutin's model assumptions. As the distance from the blade increases, the sound wave for both parabolic and 4-digital blades turns into the plane wave. Nevertheless, the pressure level of the 4-digits blade is higher 6 Db than the one for parabolic blade. The calculation data can be used for modeling of the cross-section of the helicopter's blade shape to reduce the rotational noise. [ABSTRACT FROM AUTHOR] |
