The results of an experimental and numerical comparison of the unstead
iness and shock motion that occurs in the tip region within a modern,
low-aspect-ratio, high-through-flow, axial-how transonic fan rotor are
presented, The unsteadiness studied here is associated with local phe
nomena within the blade passage and not related to blade row interacti
on, Unsteady static pressures were measured at the casing over the rot
or that operates at a tip relative Mach number of 1.6. An unsteady thr
ee-dimensional Navier-Stokes computational study was performed with ti
p clearance comparable to the test rotor. The fully three-dimensional,
unsteady, Reynolds-averaged Navier-Stokes equations were solved with
time steps, each nominally of 2.8 x 10(-5) s in duration or approximat
ely live times blade pass frequency. The results in the clearance gap
were retained from the computational solution and compared with the ex
perimental measurements. Both indicated deterministic unsteadiness nea
r the location of the shock, nigh levels of unsteadiness were also mea
sured downstream of the shock in the path of the clearance vortex, but
this phenomenon was not predicted by the computation, The unsteadines
s near the shock was shown to be a result of movement of the shock. Th
e amplitude and frequency of shock position oscillation was estimated
from the results to be about 2% chord and 2 kHz, respectively, Analysi
s of loss caused by the shock unsteadiness suggested that losses becau
se of shock motion were insignificant relative to the steady shock los
s at the relative Mach number studied.