Interactive Nozzle

Glenn Research Center

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.

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.

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 the sliders located to the right of 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 blue buttons are used to select the interactive input panels.
3. On the middle 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. Details of the input variables are given below.
4. At the right bottom 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, and labels are given in red or blue letters. Details of the output variables are given below.

GRAPHICS

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 and free stream conditions are also noted.

INPUT VARIABLES

The input variables are located at the middle right and are tagged with a red label, depending on the type of input: graphics, geometry, and flow. You can select the type of input by clicking the appropriate blue button at the top right. 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.

• If you select the Geometry input, you can use the choice button to choose either a pure convergent nozzle or a convergent-divergent (CD) geometry. You must specify the throat area (Ath) and the area ratio (Aex/Ath) for a CD nozzle.
• If you select the Flow input, you must provide the chamber total pressure (Pto), total temperature (Tto), free stream static pressure (Pfs), and the ratio of specific heats for the gas (Gamma).
• If you select the Graphics input, you can resize the graphics to see the entire nozzle by using the "Zoom" slider to the right. Or you can change the length of the nozzle by using the "Length" slider.

NOTE: 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.

OUTPUT VARIABLES

Output variables are located near the red Output: label. At the top of the output group is the thrust of the nozzle (F) as given by the thrust equation. The thrust depends on the mass flow rate (Mass) through the nozzle and on the exit velocity (Uex), which are displayed below the thrust. 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.

• Rockets:
• Nozzle:
• Interactive Nozzle Flow:

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byTom Benson
Please send suggestions/corrections to: benson@grc.nasa.gov