Fibre-optic sensor design and strain-response analysis to wall pressure fluctuations in turbulent partially-filled pipe flows

Many studies exist analysing dynamics of pressure-driven flows, yet the number of studies quantifying hydrodynamic relations in partially-filled gravity-driven pipe flows remains limited. This work presents strain data for two uniform, steady flow regimes from a novel streamwise, flush-mounted fibre-optic sensor embedded in the interior wall of a partially-filled pipe. The sensor responds to turbulence-induced pressure fluctuations at the wall, transducing them into measurable strain via a custom plate-gel structure. This sensor represents the first of its kind for non-invasive response to wall pressure fluctuations in partially-filled pipes. Cross-correlation analysis recovered bulk flow velocity estimates within 5% of the true velocity. A Metropolis–Hastings-based automated filtering process identified the frequency range retaining bulk flow properties while removing noisy measurements, further refining velocity estimates. The identified streamwise correlation pattern agreed with experimentally observed wall pressure correlations. Results suggest streamwise correlations decay at a rate proportional to the hydraulic radius in each regime, with only a 7% discrepancy between regimes. Furthermore, spectral analysis indicates the sensor’s sensitivity to coherent large-scale turbulent structures from wall data alone, a capability not previously demonstrated experimentally, suggesting potential for monitoring flow structures beyond bulk conditions. Out-of-water tests produced uninformative results, confirming that in-flow placement captures genuine flow dynamics. These findings demonstrate a novel sensing approach to monitoring partially-filled pipe flows, providing both bulk property estimation and insights into multi-scale flow structures from data collection at the wall, making way for a new form of sensor to be deployed for monitoring these flows in varying industrial contexts.