Noise constraints is one of the limiting factors for helicopter operation. It is therefore necessary to minimise the perceived noise on the ground. This can be achieved by modification of the flight path of the helicopter in such a way that noise intense flight conditions are avoided and noise is redistributed to less noise sensitive areas. The presence of wind has influence on the flight conditions of the helicopter and also on the propagation of sound from the helicopter, through the atmosphere, to the ground. To take into account the effects of wind, wind gradients and temperature gradients the computational method at DLR is extended with a ray tracing algorithm. The effects of wind are illustrated for a monopole sound source and for a complete helicopter approach with the EC135. The shape and level of the sound exposure level contours right below the flight path are mostly affected by changes in flight conditions, .i.e. changes in acoustic source. The contours further away from the flight path are mostly affected by changes in the propagation of sound. The effects of wind are most pronounced for the case of a head or side wind.
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