Episode 8. A journey to PIV flow measurements at ship scale.

Sea Trials Model Tests

After all, the optical and mechanical components of the new PIV unit (FlowPike) were manufactured and delivered to MARIN, and the final assembly and testing took place. Special attention during the assembly process was given to securing all the bolts inside the unit to prevent them from coming loose due to exposure to vibration when installed in the vicinity of a cavitating propeller.
The testing was performed in MARIN workshops as well as in MARIN’s Deepwater towing tank. In the dry, the working of all the subsystems were tested (cameras, laser, electrical motor for turning, pressure-tightness of the containment, fit and alignment of cable conduits, etc.). Then, the cameras and the laser were aligned using a specially ordered calibration plate, after which they were tightly secured in place.
Once all this was done in the dry, the unit was closed and placed under water. There, the system was calibrated using the same large calibration plate previously used for alignment. After successfully calibrating the unit, the final test was to mount the unit onto the tank carriage and perform a day of testing in the basin. During the test, runs with increasing speed were performed. The PIV unit was pointed into the flow, and its measurement area is vertical, with the main component of velocity directed through the laser sheet; this is the same configuration as in the intended application on the full-scale vessel. The resulting free-stream velocity can be compared to the speed of the carriage, which was increased from 0.5 m/s to 4 m/s. The PIV unit was able to measure the velocity with several per cent errors.
The final field of view of the unit was approximately 0.6 m wide by 1.5 long, with the centre of the area being 2.5 m away from the device. The FlowPike is therefore able to measure a 10-degree wide sector of the flow, starting at approximately 1.7 m away from the device, and up to 3.3 m away. By rotating the device, a total angle of 160 degrees can be measured. The measurement frequency is 10 Hz.  
With this, the testing of the FlowPike was considered complete and the unit was declared ready for deployment.

To be continued…

PIV unit being tested in the towing tank

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