Thermal image velocimetry for rapidly rotating fluid dynamics applications

In experimental fluid dynamics, one challenging aspect is the measurement of fluid velocity. The most prevalent method for measuring fluid velocity in the laboratory is Particle Image Velocimetry (PIV), which uses the tracking of neutrally-buoyant particles.

It then becomes challenging to use PIV in certain geometries, for instance when one aims to measure velocity on a curved surface instead of a plane.

Here, as an alternative to PIV, we investigate how measurements of the temperature at the free surface of a fluid could be used to retrieve velocity fields. We focus on a free-surface convective flow, where the surface temperature field can be measured very precisely using an Infrared Camera.

Under the assumption that the temperature field is mainly advected by the flow, our hypothesis is that tracking thermal structures can allow to derive velocity fields. We employ a dense optical flow methods with physics-based correction to track the temperature field’s structure.

We present here a benchmark study using synthetic data from2D advection diffusion simulations with ideal flow and quasi-geostrophic simulations reproducing the “Coreaboloid” experimental setup (Lonner et al, 2022). We have obtained promising results that are very close to the actual velocity field. This enables us to investigate the physics of this problem, particularly Rossby wave propagation. These encourage further application on experimental data, including this setup but also to measure velocity fields at the surface of a shallow paraboloid fluid layer.