Lighthill Waves In: Fluids Pdf

Here, (c_0) is the speed of sound in the ambient medium, and (T_ij) is :

[ \frac\partial\partial t(\rho u_i) + \frac\partial\partial x_j(\rho u_i u_j) = -\frac\partial p\partial x_i + \frac\partial \tau_ij\partial x_j ]

[ \frac\partial \rho\partial t + \frac\partial\partial x_i(\rho u_i) = 0 ]