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Interactive Nozzle

With this simulation 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.

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.

Please note: the simulation below is best viewed on a desktop computer. It may take a few minutes for the simulation to load.

Screen Layout

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 select 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. select the bar and move it along the line. If you lose the schematic, select 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.

Input Variables

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.

Output Variables

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.

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