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convergent-divergent nozzle[kən¦vər·jənt də¦vər·jənt ′näz·əl]
A nozzle in which supersonic velocities are attained; has a divergent portion downstream of the contracting section. Also known as supersonic nozzle.
An arrangement in which the forward portion of the nozzle is convergent, which increases the pressure of the exhaust gases, while the aft section is divergent to increase gas velocity to the supersonic speed and avoid losses from underexpansion. This arrangement is not very efficient below the design speed.