Particle Levitation Velocimetry for boundary layer measurements in high Reynolds number liquid helium turbulence

Abstract: Understanding boundary layer flows in high Reynolds number (Re) turbulence is crucial for advancing fluid dynamics in a wide range of applications, from improving aerodynamic efficiency in aviation to optimizing energy systems in industrial processes. However, generating such flows requires complex, power-intensive large-scale facilities. Furthermore, the use of local probes, such as hot wires and pressure sensors, often introduces disturbances due to the necessary support structures, compromising measurement accuracy. In this paper, we present a solution that leverages the vanishingly small viscosity of liquid helium to produce high Re flows, combined with an innovative Particle Levitation Velocimetry (PLV) system for precise flow-field measurements. This PLV system uses magnetically levitated superconducting micro-particles to measure the near-wall velocity field in liquid helium. Through comprehensive theoretical analysis, we demonstrate that the PLV system enables quantitative measurements of the velocity boundary layer over a wall unit range of $44\le y^{+}\le 4400$, with a spatial resolution that, depending on the particle size, can reach down to about 10~$\mu$m. This development opens new avenues for exploring turbulence structures and correlations within the thin boundary layer that would be otherwise difficult to achieve.