NOISE FIELD OF A ROTATING PROPELLER IN FORWARD FLIGHT

The propeller blade is replaced by a source and doublet distribution referring to the acceleration potential. In the linearized approach used here, these distributions are situated at the helicoidal surface described by the propeller. The doublet distribution leads to a lifting surface problem, whereas the source distribution corresponds to a thickness problem for a usually nonsymmetrical blade. These problems can be solved independently. Results have been obtained for the pressure variations and for the noise level in certain points due to each of the two cases. It appears that the noise levels are of the same order of magnitude for the two cases. The essential step in the solution is the calculation of the field due to a source moving along a helicoidal line. This field has been obtained in the form of a parameter representation. The calculation of the field due to a doublet moving along a helicoidal line also has been performed.