High-Reynolds-number turbulence in small apparatus: Grid turbulence in cryogenic liquids

Liquid helium at 4.2 K has a viscosity that is about 40 times smaller than that of water at room temperature, and about 600 times smaller than that of air at atmospheric pressure. It is therefore a convenient fluid for generating in a table-top apparatus turbulent flows at high Reynolds numbers that require large air and water facilities. Here, we produce turbulence behind towed grids in a liquid helium chamber that is 5 cm² in cross-section at mesh Reynolds numbers of up to 7 × 10⁵. Liquid nitrogen is intermediate in its viscosity as well as refrigeration demands, and so we also exploit its use to generate towed-grid turbulence up to mesh Reynolds number of about 2 × 10⁴. In both instances, we map two-dimensional fields of velocity vectors using particle image velocimetry, and compare the data with those in water and air.