  This paper documents results from a recent computational study aimed at
de-sensitizing fan stage aerodynamics---in a modern, high bypass ratio
aero-engine---to the effects of rear-seal leakage flows. These flows are the
result of seal erosion between a rotor and stator disk in an engine, and
deterioration over the life of an engine. The density-matching technique for
optimization under uncertainty was applied to this problem. This involved RANS
and adjoint flow solves of a full fan stage carried out at two different
leakage conditions. Here a detailed analysis of the fan stage aerodynamics is
carried out to determine why exactly the new design is more insensitive to the
effects of leakage flows. Specifically, it is shown that this insensitivity is
attributed to three main factors: a slight rearward shift in loading, and thus
a reduction in incidence; a reduction in the cross-passage pressure gradient;
and a re-acceleration of the flow towards the trailing edge, which prevented
any corner separation.
