High-precision interferometric measurement of rapid temperature changes in convective flow

Using interferometry, we measure rapid temperature variations in convective flow to within a few mK. This is enabled by the fast response time and high sensitivity of the interferometer to minute changes in the refractive index of the test fluid caused by temperature variations. These features allow us to detect the signature of fine fluid dynamical patters in convective flow in a fully non-intrusive manner. For example, we are able to observe an asymmetry in the rising thermal plume (i.e. an asynchronous arrival of two counter-rotating vortices at the measurement location), which is not possible to resolve with more traditional (and invasive) techniques, such as RTD (Resistance Temperature Detector) sensors. These findings, and the overall reliability of our method, are further corroborated by means of Particle Image Velocimetry and Large Eddy Simulations. The non-intrusive nature of this method, along with its robustness and 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.