Experimental study on the frequency characteristics of cloud cavitation on a full-spade rudder of a ship

Abstract

The frequency characteristics of cloud cavitation on a full-spade rudder are investigated using a cavitation image processing technique and cavitation noise analysis. The rudder deflection angle is varied from ？8° to ？15° to generate cloud cavitation on the rudder surface. For images recorded at 103 fps (frame per second), reference values for detecting cavitation are defined and calculated in red？green？blue and hue？saturation？lightness color spaces to quantitatively analyze the amount of cavitation. At a rudder deflection angle of ？12°, the amount of cavitation generated by a three-dimensional (3D) twisted full-spade rudder is found to be reduced by ∼60% compared with that generated by a flat-type full-spade rudder. The intrinsic frequency characteristics of cloud cavitation are also obtained from time-series data of the cavitation amount and are found to be the same through analysis of the noise signal measured by a hydrophone. The peak value of acoustic noise appears in the frequency band 30？50 Hz in the flat-type full-spade rudder; however, it is substantially decreased in the 3D twisted full-spade rudder at rudder angles of from ？8° to ？15°, where a noise-reduction effect is observed in the frequency band corresponding to the peak value. ？ 2022 Elsevier Ltd