Rayleigh’s Equation describes the relationship between the pressure fluctuations ($p$) and the velocity fluctuations ($u$) associated with acoustic waves in a fluid. It accounts for the compressibility of the fluid and the propagation characteristics of sound waves. Rayleigh’s Equation is a partial differential equation and can vary depending on the specific assumptions and conditions of the problem. In one-dimensional form, it can be expressed as:

Where:

• $p$ is the pressure fluctuation (Pa),
• $t$ is time (s),
• $c$ is the speed of sound in the fluid (m/s),
• ∇2 is the Laplacian operator, representing the spatial variation of pressure.