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Interactive Nozzle


This is the beta version 1.3g of the Nozzle Simulator program, and you are invited to participate in the beta testing. If you find errors in the program or would like to suggest improvements, please send an e-mail to

Due to IT security concerns, many users are currently experiencing problems running NASA Glenn educational applets. The applets are slowly being updated, but it is a lengthy process. If you are familiar with Java Runtime Environments (JRE), you may want to try downloading the applet and running it on an Integrated Development Environment (IDE) such as Netbeans or Eclipse. The following are tutorials for running Java applets on either IDE:

With this software you can investigate how a turbojet or rocket nozzle produces thrust by changing the values of different factors that affect thrust. By changing the shape of the nozzle and the flow conditions upstream and downstream, you can control both the amount of gas that passes through the nozzle and the exit velocity.

There is another version of this program that has been modified for rocket nozzles. With the rocket version, you can specify a wider variety of propellant combinations.

You can download a copy of the program to run off-line on your computer by clicking on this yellow button:

Button to Download a Copy of the Program

NOTE: If you experience difficulties when using the sliders to change variables, simply click away from the slider and then back to it. If the arrows on the end of the sliders disappear, click in the areas where the left and right arrow images should appear, and they should reappear.

If you see only a grey box at the top of this page, be sure that Java is enabled in your browser. If Java is enabled, and you are using the Windows XP operating system, you need to get a newer version of Java. Go to this link:, try the "Download It Now" button, and then select "Yes" when the download box from Sun pops up.


The program screen is divided into four main parts:

  1. On the left of the screen is a graphics window in which you can display a drawing of the nozzle you are designing. You can control the appearance of the graphics by using your mouse and the slider located in the graphics window. Details are given in Graphics.
  2. On the top right of the screen are choice buttons to select the type of nozzle you are designing and to choose between English and metric units for input and output. The red "Reset" button is used to return the program to its default conditions.
  3. At the middle right of the screen is the output from the program displayed in output boxes. By convention, input boxes have a white background and black numerals, output boxes have a black background and green numerals. Details of the Output Variables are given below.
  4. On the bottom right of the screen are the interactive inputs to the program. Inputs to the program can be made using sliders or input boxes. To change the value of an input variable, simply move the slider. Or click on the input box, select and replace the old value, and hit Enter to send the new value to the program. The input panel to be displayed is chosen by using the choice button at the top. Details of the Input Variables are given below.


On the left is a schematic drawing of the nozzle you are designing. Flow is from left to right through the turbojet nozzle and from top to bottom for the rocket nozzle. The chamber (or plenum) conditions are noted by the "Plenum-0," and the throat is at "Throat-th." The "Exit-ex" and "Free Stream-fs" conditions are also noted.

You can move the schematic in the graphics window by clicking on the figure, holding the left mouse button down and drag the schematic to a new location. You can change the size of the schematic by using the Zoom slider at the left of the graphics window. Click on the bar and move it along the line. If you lose the schematic, click on the word "Find" to restore the schematic to its default location.

You can change the length of the nozzle in the schematic by using the "Length" slider on the "Geometry" input panel. In real nozzles, the length to throat area ratio is important for keeping the flow attached. In this simulator, viscous effects are ignored, and the length is used only for "nice" graphics--it does not affect the calculation of thrust.


You can design a turbojet nozzle or a rocket nozzle by using the choice button at the top. While the physics is the same for both types of nozzles, the limits on the flow variables are typically different. A jet nozzle will have a larger throat area and a lower chamber total pressure than a rocket nozzle. Input and output can be performed using either English units or Metric units as selected by using the choice button.

The input variables are located at the lower right on three panels; geometry, flow, and propellant. You select the type of input panel by using the choice button above the panel.
  • If you select the Geometry input, you must specify the throat area Ath. For a rocket or convergent-divergent turbine nozzle, you must also specify the exit area ratio Aex/Ath. The plenum area ratio Ao/Ath and the Length of the nozzle are given for pleasing graphics, but are not used in the calculation of performance.
  • If you select the Flow input, you can change the chamber total pressure Pto, total temperature Tto, and free stream static pressure Pfs. The pressure and temperature are used in the calculation of the mass flow through the nozzle. For rocket calculations, if you change the propellants, the plenum chamber temperature is re-set to the average combustion temperature of the propellants. You may then change the chamber temperature to see its effect on thrust by using the sliders and input box on the Flow input panel.
  • If you select the Propellant input, you can change the gas which passes through the nozzle. The names of several propellants are given on the choice button next to the "Mol. Wt." label. Selecting a propellant re-sets the value of the molecular weight, the ratio of specific heats gamma and the combustion temperature . The change in molecular weight changes the gas constant used in the calculation of the mass flow through the nozzle. You can select to use a typical value for the molecular weight of the products of combustion, or you can input your own value by using the choice button. The value of the ratio of specific heats depends on the temperature of the flow, and you can use a typical curve for the variation of gamma, or input your own value by using the choice button next to the "Gamma" label. Finally, the combustion of the propellants generates a typical combustion temperature. You can use the typical value, or input your own value on the Propellant input panel by using the choice button.


Output variables are located in the middle on the right. At the top of the output group are the weight flow and the computed thrust of the nozzle. On the next line are the computed values of exit velocity and specific impulse. The exit velocity depends on the exit area Aex and the exit Mach number Mex, which are also displayed. The exit Mach number is determined by the throat Mach number Mth and the area ratio, which is input. The thrust depends also on the pressure at the exit Pex and on the overall nozzle pressure ratio NPR. The analysis used to compute these variables is based on isentropic flow through the nozzle.

Guided Tours
  • Button to Display Previous Page Rockets: Button to Return to Guided Tour Page
  • Button to Display Previous Page Nozzle: Button to Return to Guided Tour Page
  • Button to Display Previous Page Nozzle Simulator: Button to Display Next Page


Button to Display Aerodynamics Index Button to Display Propulsion Index Button to Display Model Rocket Index
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Editor: Nancy Hall
NASA Official: Nancy Hall
Last Updated: May 13 2021

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