Superfluid turbulence in converging and diverging rectangular channels

Abstract

We have extended the earlier work of Kafkalidis, Klinich, and Tough (KKT) on the effect of nonuniform flow on superfluid turbulence. The same high aspect ratio rectangular cross section flow channel is used as before, but now reversed to produce converging flow. Temperature difference data are obtained as a function of heat current for eight different positions along the channel, at four bath temperatures. After all of the data had been obtained, the channel was removed from the apparatus and cut into sections so that the actual geometry could be determined. Although designed to have a uniform height, it was found that the channel actually had a substantial height variation along its length. Incorporating this new information, we are able to show that the Schwarz theory of homogeneous turbulence in uniform flow can be simply extended to fit the weakly nonuniform flow in our channel. Data from both converging and diverging flow agree with calculations based upon the Schwarz theory applied locally but using a slightly modified value of the vortex line parameterc L . The correction toc L is about 10% independent of temperature and independent of flow direction.