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
benson@grc.nasa.gov.
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:
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:
http://www.java.com/en/index.jsp,
try the "Download It Now" button, and then select "Yes" when the download box from Sun
pops up.
SCREEN LAYOUT
The program screen is divided into four main parts:
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.
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.
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.
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.
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-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.
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.
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
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 numberMex, 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.
