  We report hot-wire measurements performed in two very different, co- and
counter-rotating flows, in normal and superfluid helium at 1.6 K, 2 K, and 2.3
K. As recently reported, the power spectrum of the hot-wire signal in
superfluid flows exhibits a significant bump at high frequency (Diribarne et
al. [1]). We confirm that the bump frequency does not depend significantly on
the temperature and further extend the previous analysis of the velocity
dependence of the bump, over more than one decade of velocity. The main result
is that the bump frequency depends on the turbulence intensity of the flow, and
that using the turbulent Reynolds number rather than the velocity as a control
parameter collapses results from both co- and counter-rotating flows. The
vortex shedding model previously proposed, in its current form, does not
account for this observation. This suggests that the physical origin of the
bump is related to the small scale turbulence properties of the flow. We
finally propose some qualitative physical mechanism by which the smallest
structures of the flow, at intervortex distance, could affect the heat flux of
the hot-wire.
