de Laval Convergent–Divergent Nozzle

Pinched convergent–divergent duct that chokes compressible gas flow to Mach 1 at the throat and expands it to supersonic speed.

Specifications & Metrics

type: Aerospace & Rocket Propulsion
working principle: Isentropic compressible flow acceleration via area–velocity relation: (dA/A) = (Ma² − 1)(dv/v)
operating regime: Throat choked at Ma = 1.0; supersonic exit (Ma > 1, exhaust velocities 1,700–4,500 m/s in chemical rockets)
efficiency or isp: Converts thermal enthalpy into axial kinetic energy; chemical rocket I_sp = 200–455 s
originator: Ernst Körting (1878), Gustaf de Laval (1888 steam turbine), Robert H. Goddard (rocket nozzle)

Patented in 1888 by Swedish engineer Gustaf de Laval to accelerate steam Jets for his impulse steam turbine and first applied to liquid-fueled rockets by Robert H. Goddard, the de Laval nozzle exploits the sign reversal of compressible gas dynamics at Mach 1.
In the converging section, subsonic gas accelerates as cross-sectional area narrows until it reaches sonic velocity (Mach 1.0, 'choked flow') at the minimum-area throat; past the throat, the diverging bell allows the supersonic gas to expand and accelerate further while its temperature and static pressure drop.
In rocket engines, the de Laval nozzle converts combustion-chamber thermal energy at ~3,500 K and 7–30 MPa into axial exhaust velocities of 2,900 to 4,500 m/s (Mach 3 to 5+).