Measurement of nuclei content by digital holography in a free surface cavitation tunnel

Cavitation test results of identical bodies obtained in different cavitation tunnels sometimes differ from each other. One main reason for this is the influence of gas and nuclei content in the water. The knowledge of the water quality in the tunnel is crucial for comparing different results and for transferring them to full scale. Holography is a very promising optical technique for the measurement of cavitation nuclei, not least because of its accuracy, reliability, and repeatability at relatively low costs for its setup. First inline holography measurements have been performed at the cavitation tunnel K27 of TU Berlin with a preliminary setup. The K27 has a free water surface and therefore a high degassing behaviour. Selected measurements have been analysed and their results are shown here. Possible improvements for the test setup are considered. An inline digital holography configuration with laser and camera inside of the test section seems promising.