  The interaction of an impinging shock and a supersonic helium cooling film is
investigated experimentally by high-speed particle-image velocimetry. A laminar
helium jet is tangentially injected into a turbulent air freestream at a
freestream Mach number $Ma_\infty=2.45$. The helium cooling film is injected at
a Mach number $Ma_i=1.30$ at a total temperature ratio
$T_{0,i}/T_{0,\infty}=0.75$. A deflection $\beta=8\deg$ generates a shock that
impinges upon the cooling film. A shock interaction case and a reference case
without shock interaction are considered. The helium mass fraction fluctuations
are measured and the turbulent mass flux as well as the turbulent Schmidt
number are determined qualitatively. For comparison, large-eddy simulation
(LES) results of a comparable flow configuration are used. The streamwise and
wall-normal turbulent mass fluxes are in qualitative agreement with the LES
data. The turbulent Schmidt number differs significantly from unity. Without
shock interaction, the turbulent Schmidt number is in the range $0.5 \leq Sc_t
\leq 1.5$ which is in agreement with the literature. With shock interaction,
the turbulent Schmidt number varies drastically in the vicinity of the shock
interaction. Thus, the experimental results confirm the numerical data showing
a massively varying turbulent Schmidt number in supersonic film cooling flows,
i.e., the standard assumption of a constant turbulent Schmidt number is valid
neither without nor with shock interaction.
