De Laval Nozzles for the Use of Rocket Propulsion

by Matthew Carlson

Submitted : Fall 2017

         Rocket nozzles, and more generally De Laval nozzles or convergent-divergent nozzles, are one of the key components that allow modern day rockets and jet aircraft to take flight.  Named after its inventor, Swedish chemist Gustav De Laval, the De Laval nozzle allows for the rapid acceleration of exhaust gases needed to create sufficient thrust to propel a rocket.  These nozzles rely on the principles of conservation of mass and conservation of momentum, as well as the properties of fluids to cause the change in velocity.  Within the first part of the nozzle, the converging end, fuel is ignited.  The burning solid or liquid fuel rapidly expands as it becomes a gas, creating pressure within the converging end of the nozzle.  As this pressure forces exhaust gas through the converging end into the throat of the nozzle, the gases must accelerate to maintain a constant flow rate due to the conservation of mass and momentum.  Within the throat, the exhaust gasses should reach the speed of sound, and continue accelerating within the diverging end of the nozzle.  In a properly designed nozzle, the ratio of cross sectional areas between the throat and diverging end minimizes friction, while allowing for expansion and further acceleration of exhaust gases.  If the diverging end is too tight, the gases cannot accelerate any further; likewise, if the diverging end is too wide, there is insufficient pressure to continue acceleration and negate frictional forces.  This project aims to determine an efficient shape for a De Laval Nozzle.

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