Abstract:
Turbulence, both classical and quantum, represents an intellectual challenge in understanding many natural phenomena. Turbulence in quantum fluids such as He II or ³He B - quantum turbulence- involves a dense tangle of quantized vortex lines and its relationship to classical turbulence in incompressible fluids described by Navier-Stokes equations is not obvious. There are important differences between the two, arising due to two-fluid phenomena and quantization of circulation in superfluids, but in many respects the relationship between quantum and classical turbulence is remarkably close, especially if quantum turbulence is generated in a classical way, e.g., in a flow past obstacle such as a sphere or by towing a grid of bars through a stationary sample. Surprisingly, close links to classical turbulence are found even if quantum turbulence is generated thermally in a counterflow He II channel. We discuss recent experiments on cryogenic helium turbulence and their theoretical aspects, emphasizing those performed in the Joint Low Temperature Laboratory in Prague-Troja.