Advanced measurements of rim-driven tunnel thrusters -The Wageningen TT-series JIP

For the Wageningen TT-series JIP a rim-driven tunnel thruster test set-up was used to evaluate the cavitation dynamics, underwater radiated noise levels (URN), pressure fluctuations on the inside of the tunnel, loads on the propeller, and dynamic generated side forces on the ship hull. Experiences with this complex test set-up are discussed in this paper. As there are too much elements in the setup to be discussed down to the last detail, this paper will point out the general components and will go into detail on noise measurements and the calibration of a 6-component frame.
The calibration and check loads of one of the 6-component frames are presented. An elaborate paragraph on noise measurements discusses the calibration of the hydrophones, determination of the acoustic transfer of the set-up and signal quality. The analysis of the noise measurements showed disturbances in signals recorded by 2 out of 3 hydrophones. Although not yet completely pinpointed, these disturbances are ascribed to unwanted electromagnetic current, inadequate grounding or engine control switches. Other issues present during measurements were warming of bearings, Bernoulli effects between static and rotating segments of the set-up, and calcification and creep of sensors after long time submergence of the set-up. In the near future extra effort will be put in to tackle these challenges. Nevertheless, this complex set-up with in-house developed, as well as off the shelf sensors answers to the demanding research questions asked in the TT JIP.