Inviscid irrotational flow around a pair of coaxial disks is c
onsidered in the limit in which the
distance
2
h
between the disks is small compared to their radius
a
. The disks have zero thickness and
accelerate away from one another along their common axis. Th
e added mass
M
of each accelerating
disk is increased by the presence of the other disk. Analytic
predictions are obtained when
h/a
≪
1
,
with
M
∼
πa/
(8
h
)
−
ln(
h/a
)
/
2 + 0
.
77875 +
· · ·
. The term
O
(
a/h
)
can be obtained by means
of an inviscid analysis of approximately unidirectional flo
w within the gap between the disks, but
the correction terms have not been reported previously. The
irrotational flow problem satisfies Neu-
mann boundary conditions on the surface of the disks, but is o
therwise analogous to the Dirichlet
problem of the capacitance of a pair of charged disks, which h
as been the subject of much study and
controversy.