Experimental evidence of homogeneous superfluid turbulence in large-pore porous media

Experimental results are presented for counterflow and isothermal coflow through large-pore porous materials, with porosities greater than 90% and permeabilities of order 10-11 m2. Counterflow velocities ranging from 0.06 to 0.14 m/s were obtained. Because of the large-pore geometry, and the velocity range investigated, the superfluid is fully turbulent. The counterflow data are well described by the two-fluid model using the Schwarz model of homogeneous mutual friction, with a larger, empirically-modified, mutual friction coefficient. The same mutual friction model is applied to the coflow results, assuming that dissipation due to superfluid vortex interaction with the wall of the porous media is negligible. In this case, the normal-fluid and superfluid velocities are coupled through the mutual friction, and relative velocities in the range 0.00 to 0.10 m/s, the authors calculate relative velocities up to 0.07 m/s, and normal-fluid velocities in excess of 0.04 m/s. An interesting feature of the coflow pressure drop, as a function of the normal-fluid velocity, is that it is larger than the counterflow pressure drop by the ratio of the total density to the normal-fluid density