isentropic

Isentropic isentropic describes a process or flow in which the entropy of the system remains constant. In thermodynamics and fluid mechanics, an isentropic process is typically considered reversible and adiabatic, meaning no heat is exchanged with the surroundings and no irreversibilities produce entropy. As a result, the entropy S remains unchanged (S2 = S1).

For an ideal gas, an isentropic process satisfies p = K rho^gamma, where gamma = Cp/Cv. Equivalently, the pressure ratio p2/p1 equals the density ratio raised to gamma, and the temperature ratio follows T2/T1 = (p2/p1)^((gamma-1)/gamma). The density ratio is rho2/rho1 = (p2/p1)^(1/gamma). These relations form the basis for calculating changes in pressure, temperature, and density during isentropic compression or expansion.

In fluid dynamics, isentropic flow assumes an inviscid, thermally insulated fluid with no shocks and no heat transfer, so entropy is constant along a streamline. Under these conditions, velocity, pressure, and density vary in a way described by the isentropic relations; the speed of sound is a = sqrt(gamma R T) for an ideal gas.

Stagnation properties are often used in nozzle and diffuser analysis. The stagnation temperature T0 remains constant, given by T0 = T(1 + (gamma-1)/2 M^2), and the stagnation pressure relates to the static pressure via p0/p = (1 + (gamma-1)/2 M^2)^{gamma/(gamma-1)}.

Applications include nozzle design, aircraft engine thermodynamics, and turbomachinery. Limitations: real flows exhibit viscosity, heat transfer, and irreversibilities that generate entropy, so true processes are only approximately isentropic.