Numerical and Experimental Analysis of a Singing Propeller Having Blunt Trailing Edges

This study considers a blunt trailing-edged propeller operating both in a uniform and a nominal wake fields. Experiments are performed in the cavitation tunnel of Hyundai Maritime Research Institute. The effects of propeller rotation speed, tunnel flow speed, and blade sheet cavitation growth on the generation mechanism of the singing propeller are investigated. The cavitation, sound, and vibration characteristics related to the singing phenomena are measured by a hydrophone, a microphone, an accelerometer, and a highspeed digital camera. The natural frequencies of propeller blades are predicted using a finite element method and verified by both contact- and noncontact-type impact hammer tests in air and underwater conditions. The inflow speed and angle of attack for each section of the propeller blades are calculated using the Reynolds-averaged Navier-Stokes equation-based flow analysis. Using a detached eddy simulation, the vortex shedding patterns and their frequencies are calculated. The predicted vortex shedding frequencies are compared with the measured singing frequency and blade natural frequency for determination of consistency. Under cavitation-free regime, the vortex shedding frequencies are predicted for normalized blade radial positions of .8R and .9R. The computed values are close to the two blade natural frequencies and also consistent with the double singing phenomena in the cavitation tunnel test. For fully developed blade sheet cavitation condition, the vortex formation in the wake region is observed to be strongly influenced by the cavitation growth on the pressure side surface. Propeller singing is diminished with the continuous growth of cavitation and is finally locked-off. The significant variation of the flow-induced sound and vibration levels are also observed for the locked-in and the locked-off conditions. The singing occurrence location and frequency under uniform inflow condition are analyzed to investigate the generation mechanism of propeller singing. This study can be applied to the analysis of singing location and its frequency of a propeller operating in the hull wake, which changes the angle of attack according to the propeller rotation angle.