  We consider classical fluids in non-relativistic framework. The flow is
considered to be barotropic, inviscid and rotational. We study the linear
perturbations over a steady state background flow. We find the acoustic metric
from the conservation equation of a current constructed from linear
perturbation of first order derivatives (in position and time coordinate) of
Bernoulli's constant (scalar field) and vorticity (a vector field). We have
rather shown that the conservation equation of current reduces to a massless
scalar field equation in the high frequency limit. In contrast to the
contemporary works, our work shows that even if we can not find a wave equation
(in rotational flow) which is structurally similar to a massless scalar field
equation in curved space-time, but still an analogue space-time exists through
a conservation equation. Considering velocity potential and Clebesch
coefficients, we find that only for some specific systems current conservation
equation can be found yielding the same analogue space-time. We conclude that
for rotational flows, it is wise to study linear perturbation of Bernoulli's
constant over the velocity potential and Clebsch coefficients.
