As sound is a propagating pressure wave. it is important to obtain the hydrodynamic pressure oscillations in the fluid to calculate propeller noise. Numerical hydroacoustic simulations generally assume incompressible flow. Time delays in sound propagation are neglected due to the incompressibility assumption. https://www.markbroyard.com/best-save-happy-way-ashy-bines-whey-protein-powder-choc-caramel-500g-online-sale-big-deal/