Nuclei, or microbubble, populations control the inception and dynamics of cavitation. It is therefore important to quantify distributions in cavitation test facilities to rigorously model nucleation dynamics. Measurements of natural nuclei population dynamics were made in two test facilities in Australia and Japan via mechanical activation using a Cavitation Susceptibility Meter (CSM). A range of tunnel operating parameters, including pressure, velocity and dissolved oxygen (DO) content, were investigated. The DO saturation condition upstream of the test section is found to provide a threshold as to whether the population is affected by DO in the Australian test facility. Historical trends in the population are quantified, indicating that regular monitoring is required. Variation of the population around the Australian cavitation tunnel circuit was studied by varying the water sampling location. Provided the water remains undersaturated, as defined above, the natural nuclei population in the test-section can be measured by sampling from the lower-limb resorber. Comparisons are made between test facilities in Australia, Japan and other countries, as well as environmental waters, using different measurement techniques. Optical and acoustic methods show microbubbles in the size range of 10 to 100 µm typical of those used to
Tip vortex cavitation (TVC) inception and desinence behaviour of a NACA 0012 cross-section, elliptical hydrofoil is investigated from a statistical perspective in a cavitation tunnel. Measurements were made for incidences from 4 • to 16 • and Reynolds numbers from 1.0×10 6 to 2.1×10 6 . The statistics of TVC inception were quantified by taking repeated measurements of the time until the appearance of a tip vortex cavity for a range of fixed incidences. In other experiments, the angle of attack was continuously increased until inception then decreased until desinence for a range of fixed cavitation numbers. The data were primarily acquired via an automated process using a laser and photodiode to detect the presence of a cavity. Measurements show that TVC inception in a nuclei deplete flow is a probabilistic process for which a large dataset is required for accurate characterisation. The probability of ingesting and activating a nucleus increases with time at a given test condition due to the increased volume of water exposed to low pressures. TVC desinence exhibits far less statistical variation than inception and is largely independent of the natural nuclei population. It does, however, exhibit hysteresis which is dependent on the topology of the cavitating flow. For the desinence of unattached cavitation, there is a small hysteresis between the inception and desinence indices. However, desinence is delayed for attached cavitation.
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