Sound of fluids at low mach numbers

The sound of fluid at low Mach number is a special research area that poses diverse applications not only in aerodynamics but also in bio-medical or biological fluids. The related Mach numbers are in the order of O(10 ^-2) or even less and therefore the compressibility effects are substantially low but still play an important role in many aspects. A hybrid method of splitting the hydrodynamic field and the acoustic field is of our present interest and attention is given to the linearized perturbed compressible equations (LPCE). In this paper, the linearized perturbed compressible equations are reviewed with some discussion on the acoustic source term, -DP/Dt. A few selected applications of aerodynamic noise and bio-fluid sound are demonstrated by the present hybrid method.