Cavitation Luminescence from Flow over a Hydrofoil in a Cavitation Tunnel
This paper describes a photon-counting study of the cavitation luminescence produced by ﬂow over a hydrofoil. This has previously been identiﬁed in water saturated with xenon. The four objectives of this study are: to determine whether luminescence can be obtained using air-saturated water; to quantify this emission, if it is present, as a function of ﬂow parameters; to determine whether the photon arrivals occur with random timing, or in ‘bursts’; to put limits on the rates associated with any bursts. The ﬂow experiments were performed in a cavitation tunnel capable of achieving ﬂow velocities of up to about 50ms−1 in the test section. The experimental hydrofoil was a NACA 009 blade. Parameters varied were the ﬂow velocity, the incident angle of the hydrofoil and the cavitation index. The results show that signiﬁcant photon counts are recorded when leading-edge cavitation takes place and U-shaped vortices (cavities) are shed from the main cavity. The photon count increases dramatically as the ﬂow velocity increases or the cavitation index is reduced. Departures from a Poisson distribution in the arrival times of photons at the detector suggest the presence of ‘bursts’. These may be related to the way vortices are shed from the main cavity. Limits are inferred on the detection rates associated with bursts.