A new numerical algorithm for acoustic noise generation is developed. The a
pproach involves two steps comprising an incompressible flow part and an in
viscid acoustic part. The acoustic part can be started at any time of the i
ncompressible computation. The formulation can be applied both for isentrop
ic flows and non-isentropic flows. The model is validated for the cases of
an isentropic pulsating sphere and non-isentropic flows past a circular cyl
inder. In the latter case the computations show that the generated acoustic
field in addition to the dominant Strouhal frequency, f(0), contains a sli
ghtly higher frequency, f(2), and a modulating lower frequency, f(1) = f(2)
- f(0). Numerical experiments with different interpolation schemes, bounda
ry conditions, etc., show that the appearance of these modes is not an arti
fact from the numerical discretization.