Exploration of interferometry for measuring temperature in experimental fluid mechanics

Abstract

This thesis explores the strengths and limitations of using standard interferometry to sample line-of-sight-averaged temperature in water via two experimental setups: slow-varying temperature in static fluid and fast temperature variations in convective flow. The fast response time and high precision of the measurements obtained (a few mK) is enabled by the high sensitivity of the interferometer to minute changes in the refractive index of water caused by temperature variations. These features enable the detection of fine signatures imprinted by fluid dynamical patterns in convective flow in a fully non-intrusive manner. For example, an asymmetry in the rising thermal plume (i.e. an asynchronous arrival of two counter-rotating vortices at the measurement location) is observed, which is not possible to resolve with more traditional (and intrusive) techniques, such as RTD (Resistance Temperature Detector) sensors. Furthermore, an exploratory model is proposed, elucidating the potential feasibility of extracting localized (line-of-sight-averaged) temperature gradients and fluid velocity by interpreting the drop in the interferometer’s visibility; by doing so, useful information may be extracted from a phenomenon (visibility drop) that is commonly an important source of error in other interferometric techniques. These findings, and the overall reliability of the proposed method, are further corroborated by means of Particle Image Velocimetry and Large Eddy Simulations. While the proposed technique presents inherent limitations (mainly stemming from the line-of-sight-averaged nature of its results and high sensitivity to mechanical disturbances), its non-intrusiveness and robustness, along with the ability to readily yield real-time, highly accurate measurements, render this technique very attractive for a wide range of applications in experimental fluid dynamics.

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Identifiers

ORCID for Xinyang Ge: orcid.org/0009-0007-0414-051X

ORCID for Sergio Maldonado: orcid.org/0000-0001-6072-122X

ORCID for Yue Zhang: orcid.org/0000-0002-5068-2260

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