  We propose a scheme of acoustic spherical cloaking by means of background
irrotational flow in compressible fluid. The background flow forms a virtual
curved spacetime and guides the sound waves bypass the cloaked objects. To
satisfy the laws of real fluid, we show that spatially distributed mass source
and momentum source are necessary to supply. The propagation of sound waves in
this system is studied via both geometric acoustics approximation and full wave
approach. The analytic solution of sound fields is obtained for plane wave
incidence. The results reveal the effect of phase retardation (or lead) in
comparison with the ordinary transformation-acoustic cloak. In addition, the
ability of cloaking is also evaluated for unideal background flows by analyzing
the scattering cross section.
