Comparative analyses of phase-detective intrusive probes in high-velocity air–water flows

Abstract

A comparative analysis of a wide range of air-water flow properties was conducted for two types of phase-detection intrusive probes including fiber-optical and conductivity probes. Experiments were conducted on a stepped spillway model for a skimming flow discharge q = 0.478 m 2 /s and for Re = 4.7 10 5 in a flow region just downstream of the inception point of free-surface aeration and in the fully developed flow region. The comparison of a large number of key air-water flow properties showed a very close agreement for the two sensor types including void fraction, interfacial velocity and equivalent clear water flow depth enabling a direct comparison of past and future data collected with either phase-detection probe type. Minor differences were observed in terms of chord sizes, clustered properties and interparticle arrival times linked with the slightly smaller sensor size of the fiber-optical probe. The in-line positioning of the leading and trailing tips of the fiber-optical probe affected the trailing tip properties resulting in elevated turbulence intensities. An optimum dual-tip phase-detection probe design should consist of small probe tips positioned side-by-side.

Experimental Analysis of the Influence of Aeration in the Energy Dissipation of Supercritical Channel Flows

“…There are different proposals for energy dissipation mechanisms in open channel flows, depending on the regime analyzed. Turbulence and bubble effects play an important role in self-aerated open channels and stilling basins [13][14][15][16][17], but supercritical flows in spillways are highly influenced by roughness at the boundary [18]. The objective of the work presented in this article is to quantify the influence of aeration on the roughness boundary in high velocity and turbulent flows through friction mechanisms.…”

Numerical Simulation of Hydraulic Jumps. Part 1: Experimental Data for Modelling Performance Assessment

“…When air concentrations amount to over a few percent, the preferred instrumentation should be phase detection probes [96,97]. Special care must be taken in regions with near null velocities and important cross velocities, which lead to oblique impact of bubbles with the probes' tips or bubbles undetected by at least one tip (impacting the cross-correlation performance).…”

Best practices for velocity estimations in highly aerated flows with dual-tip phase-detection probes

“…A convergence analysis of the stepped spillway data showed that sampling durations T > 45 s could further improve the measurement accuracy (Appendix A). The raw voltage signals were recorded with the same LabVIEW-based data acquisition system using a high-speed acquisition unit (National Instruments USB-6366) and further details on the overall probe designs can be found in Felder and Pfister (2017) and Felder et al (2019). Table 3: Experimental flow condition and dual-tip phase-detection probe specifications for the re-analysed datasets; CP: phase-detection conductivity probe; FO: phase-detection fiber optical probe; Reynolds number Re = q/ν, with ν the kinematic viscosity of water and q the specific discharge; f : sampling rate, T : sampling duration; ∆ x: streamwise tip separation distance.…”

“…In the present study, experimental data at step edge 101 were re-analysed. Further details on the flume and the flow conditions can be found in Felder and Pfister (2017).…”