EMERGING ISSUES IN HELIUM TURBULENCE

It has been appreciated recently that because helium has the lowest vi scosity of any known material, it can be used in reaching the very hig hest Reynolds numbers and Rayleigh numbers. Critical helium gas, heliu m I and helium II are all candidates for such uses. Helium gas and hel ium I are classical fluids and the advantage stems solely fr om their low kinematic viscosity. Helium II obeys two-fluid equations and their use in turbulence investigations is under study. This article provide s a brief introduction and review of this topic, outlining some of the progress already made and. questions which need to be resolved as thi s relatively new field of investigation evolves. A summary of instrume ntation available is included.