Abstract
The drag coefficient on the surface of a sphere for temperatures between 1.6 K and 2.1 K has been measured in flowing He II. The measurement suggests a temperature dependence to the drag coefficient not seen in ordinary fluids and this dependence appears to correlate with the normal fluid density, ρn. The results scale with normal fluid Reynolds number, Ren=Re (ρn/ρ), based on non-dimensionalizing the He II two fluid equations. The drag coefficient has a minimum value at same normal fluid Reynolds number, Ren≈2.5×105 for each temperature. This is in reasonable agreement with the minimum in the classical sphere drag coefficient curve at approximately Re=3×105. The drag crisis is governed by the location of the boundary layer separation and this position may depend upon the normal fluid density. Recent He II measurements confirm that the drag coefficient has a temperature dependence possibly related to a variation of the turbulent transition within the boundary layer.
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