Geräuschabstrahlung von Schiffspropellern im Nachstrom

The hydrodynamic and acoustic behavior of a ship propeller is determined by its geometry, load and speed, location and by the non-uniform wake. Acoustical predictions are based either on experience with reliable propulsion systems or with restrictions on model tests. The contribution deals with results of experimental investigations of model propellers in non-uniform wake flows, carried out with a special designed facility for propeller acoustics, which operates on an natural lake. The origins of noise with its spectral properties as tonals, frequency distributions and noise modulation by the wake are discussed. Cavitation, at higher speeds unavoidable, is the predominant underwater noise source of a ship. Types of cavitation as bubble or sheet cause very different noise levels as far as uniform flow is concerned, but in non-uniform wake flows for conditions as the same propeller load and speed, the differences in noise levels diminish. Propeller vibrations are another noise source, wh ich have special acoustical line-spectra caused by the directivity pattern of excited propeller eigenfrequencies.