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Abstract

Microbubble populations within the test section of a variable-pressure water tunnel have been characterised for various operating conditions. The tunnel was operated with demineralised water and artifcially seeded with microbubbles from an arrayof generators located in a plenum upstream of the tunnel contraction. The generators produce a polydisperse population ofmicrobubbles 10–200 μm in the diameter. The microbubbles are generated from supersaturated feed water within a confnedturbulent cavitating microjet. The generator and tunnel operating parameters were systematically varied to map the range ofnuclei concentrations and size ranges possible in the test section. Microbubbles were measured with Mie Scattering Imaging(MSI), an interferometric sizing technique. A new method was introduced to calibrate the detection volume and extend thedynamic range of the MSI. The acquisition and processing of microbubble measurements with MSI have a fast turn-aroundsuch that nuclei concentration measurements are approaching real time. Estimation of the total bubble concentration waswithin 5% of the sampled concentration after only 100 detections but 104 were necessary for full histogram convergence. Thetunnel is operated with water at low dissolved gas content to ensure all injected microbubbles dissolve and do not completethe tunnel circuit. As a result of this, the injected population is altered by dissolution as well as pressure change during theshort residence between plenum and test section. The transformation is shown to be complex, changing with tunnel operatingconditions. The measured test section nuclei populations were found to follow a power law for the higher concentrations. Testsection nuclei concentrations of 0–24 mL−1 can be achieved through variation of generator and tunnel operating parameters.

Item Type:	Article
Authors/Creators:	Russell, PS and Barbaca, L and Venning, JA and Pearce, BW and Brandner, PA
Keywords:	cavitation nuclei, hydrodynamic facilities, laser based imaging, bubble size measurement
Journal or Publication Title:	Experiments in Fluids
Publisher:	Springer-Verlag
ISSN:	0723-4864
DOI / ID Number:	https://doi.org/10.1007/s00348-020-2911-2
Copyright Information:	© Springer-Verlag GmbH Germany, part of Springer Nature 2020
Related URLs:	Google Scholar: Barbaca, L Google Scholar: Venning, JA UTAS Profile: Venning, JA Google Scholar: Pearce, BW UTAS Profile: Pearce, BW Google Scholar: Brandner, PA UTAS Profile: Brandner, PA
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