Cavitation Observations at HSVA are performed in HYKAT, the large Hydrodynamics and Cavitation Tunnel. This is one of the largest circulating water cavitation tunnels in the world, featuring a closed test section without free surface. The testing philosophy is built on two major columns:
- The huge test section with dimensions of 11 m x 2.8 m x 1.6 m (L x B x H) allows installation of physically the same ship models used for propulsion tests in the towing tank before. This ensures generation of the complete and realistic three-dimensional propeller inflow by the ship model itself without wasting time and money for production of a special cavitation test model, a wire screen or a dummy. All interactions between hull, propeller(s), rudder(s) and other appendages are modeled properly by this technique.
- The missing free surface allows violation of Froude’s scaling law and running the cavitation test at highest possible tunnel water speed instead. Flow velocities up to 8 m/s and propeller speeds of 30 rps and more are typical in HYKAT. Together with the large ship and propeller models this results in large Reynolds Numbers and consequently in best cavitation similarity between model and ship.
Even more than the impressive hardware it is the correlation experience of more than 20 years with HYKAT that ensures most reliable judgment of the erosiveness of the cavitation behavior obtained in this tunnel. The deliverable provided as the result of a cavitation observation consists of a description of test set-up, procedures and conditions together with sketches, photographs and video records of the cavitation phenomena as well as a clear judgment of the cavitation behavior. Preliminary results are available right after the tests.
Together with simultaneous measurement of propeller induced hull pressure pulses the performance of cavitation observations is the standard test in HYKAT to avoid erosion and vibration problems due to bad propeller performance in full scale.