Statistical aspects of tip vortex cavitation inception and desinence in a nuclei deplete flow

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 × 10⁶ to 2.1 × 10⁶. 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 and 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.