This video lesson describes convergingdiverging nozzles, which have an hourglass shape with a minimal area in the throat region. These nozzles are used to accelerate flows to very high speeds in aircraft and spacecraft. This lesson is part of the Ansys Innovation Course: Internal Compressible Flows. To access this and all of our free, online courses — featuring additional videos, quizzes and handouts — visit Ansys Innovation Courses at https://www.ansys.com/courses.