👉 In fluid mechanics, the equivalent fluid concept refers to a hypothetical fluid that can replace a given compressible fluid under specific conditions, such as when the fluid's density changes significantly with pressure or temperature. This equivalent fluid has the same Mach number (ratio of flow velocity to the speed of sound) and Mach entropy across any interface between it and the original fluid, allowing for simplified analysis of compressible flow problems. For instance, in supersonic flows, the equivalent fluid can be thought of as an isentropic fluid with zero Mach number across the shock wave, simplifying the complex interactions and enabling easier calculations of flow behavior.
