is a beta 1.0f version of the TunnelSim Open Return 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 Thomas.J.Benson@nasa.gov.
TunnelSim - Open Return
With this software
you can investigate the design and operation of an
open return wind tunnel
by changing the geometry and flow conditions in the tunnel.
There are two versions of TunnelSim; a version for open return
tunnels and another version for
closed return wind tunnels.
This web page contains the on-line student version of the
open return program.
It includes an on-line user's manual which describes the
various options available in the program and includes hyperlinks to
pages in the
Beginner's Guide to Wind Tunnels
describing the math and science of wind tunnels.
More experienced users can select a
version of the program which does not include
these instructions and loads faster on your computer.
You can download these versions of the program to your computer
by clicking on this yellow button:
With the downloaded version, you can run the program off-line and do not
have to be connected to the Internet.
This program is designed to be interactive, so you have to work with the program.
There are a variety of choices which you must make regarding the display
of results by using a choice box.
A choice box has a descriptive word displayed and an arrow at the right of the
box. To make a choice, click on the arrow, hold down and drag to
make your selection.
The current values of the design variables are presented to you in boxes. By convention,
a white box with
black numbers is an input box and you can change the value of the number.
A black box with
yellow numbers is an output box and the value is computed by the program.
To change the value in an input box, select the box by moving the cursor into the box
and clicking the mouse, then backspace over the old number, enter a new number,
then hit the Enter key on your keyboard. You must hit Enter
to send the new value to the program.
For most input variables you can also use a slider located next to the input box.
Click on the slider bar, hold down and drag the slider bar to change values, or
you can click on the arrows at either end of the slider.
At any time, to return to the original default conditions,
click the red Reset button at the upper right of the program.
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.
If you experience difficulties when using the sliders to change variables,
simply click away from the slider and then back to it.
the arrows on the end of the sliders disappear, click in the areas
where the left and right arrow images should appear, and they
program screen is divided into five main parts:
top left side of the screen is the View Window.
The view window includes a graphic of the wind tunnel that you are
designing and a slider which control the graphic.
Details of the window
are given in the Graphics section of this page.
upper right side of the screen is the Control Panel.
The control panel holds several buttons which
invoke the input panels located in the middle right. The open tunnel
has a bellmouth, a test section and a diffuser. The selected section
is colored yellow.
You can also select the
units to be used in the calculations by using the choice button.
middle right side of the screen is the Input Panel.
Various input panels are displayed in this window.
You select the input panel by using the section
buttons on the control panel.
Details of the input variables
are given below.
lower right side of the screen is the Output Panel.
The output can be presented as
variable values in the test section of the wind tunnel.
Details of the
output variables are given below.
lower left side of the screen is the Graphics Window.
In the graphics window, you can display bar charts of the flow variables
across the wind tunnel. Details of the flow variables are given in the
The View Window contains a schematic drawing of the wind tunnel that
you are designing and some controls for the schematic drawing.
The walls of the tunnel are shown in blue
while the selected section is colored yellow. There are two views of the tunnel, one from
the top and one from the side. Flow through the tunnel goes from left to right.
The borders of the various sections of the tunnel are denoted by eight, numbered white
lines. Values of the flow variables at these locations are given in the bar graphs below
the view window.
You can move the picture within the window by moving the cursor into
the window, holding down the left mouse button, and dragging the tunnel
to a new location. You can also "Zoom" in close to the tunnel by using
the green slider at the left of the window. If you get lost, pushing
the yellow Find button will return the tunnel to the initial position.
There are two major outputs from the program. Conditions in the test section
are given at the lower right and the variation of variables at eight stations
through the tunnel
are given by bar graphs at the lower left.
You select the variable to output on the bar graphs by using the four
labeled buttons above the bar graphs. The selcted variable is shown in yellow
and the value of the variable is shown at the top of the bar.
The default bar graph
is the Velocity. The dimensions for the velocity are noted in the
test section conditions at the lower right. The velocity output is limited to
350 ft/sec because of
in the analysis.
You may also display
the Static Pressure through the tunnel. As with the velocity, the
dimension of the variable is given at the lower right.
The total pressure through the tunnel is a constant and equal to the room
static pressure which, by default, is sea-level standard pressure (14.7 psi).
You may select the
Mach number variation through the tunnel. Mach number is dimensionless
and limited to a maximum of nearly 0.3 .
The final selection is the
cross-sectional Area value at the eight stations shown in the view window.
The dimensions for the area are the square of the linear dimension shown in the input panel
(square feet or square meters).
The values of the flow variables in the test section are shown at the
The velocity and
static pressure are related through
Bernoulli's equation because the analysis is
one dimensional and no work is done on the flow through the duct. The
Reynold's number and
Mach number are calculated based on sea-level standard
day conditions, the local flow velocity, and the diameter (height) of the test section.
airflow through the tunnel is the product of the velocity
and cross-sectional area of the test section. With the air density assumed to be
constant through the tunnel, the conservation of mass provides that the airflow is
constant through the tunnel. The Diffuser Angle is the slope of the diffuser
wall expressed in degrees. In the diffuser, the static pressure is increasing as one
moves downstream. The adverse pressure gradient causes boundary layer separations in
real diffusers if the diffuser angle is much greater than 7 degrees. In this analysis a
warning light is displayed at the lower right whenever the diffuser angle exceeds 7 degrees.
Another warning light is displayed if the Mach number in any section exceeds 0.3 because the
analysis neglects compressibility effects.
The input variables
are located on input panels that are displayed at the middle left.
You can select the input section to display by using the buttons on
the control panel. You can choose to vary the Bellmouth,
the Test Section, or the Diffuser.
For any section, there
are two groups of input variables; flow variables and geometric variables.
The flow variables include the static pressure, the velocity and the airflow
as described in the Output Variables of the previous paragraph. On the input panel,
changing the value of any one of the flow variables will affect the value of the
other flow variables.
The geometric variables include the length of the section and the cross-sectional
shape and dimensions. Using the choice box, you can choose either a square, circular,
or rectangular cross-section. For the Bellmouth, the cross-section is specified at the entrance
of the wind tunnel. For the Test Section, the cross-section is assumed to be constant
from the end of the bellmouth to the beginning of the diffuser. For the Diffuser, the
cross-section is specified at the exit. As you vary the size of the side, diameter, or
width and height, the program calculates the area and uses the mass flow equation and
Bernoulli's equation to determine the velocity and pressure.
The Education Programs
Office will continue to improve and update TunnelSim based on user input.
Changes from previous versions of the program include:
On 16 July 09,
version 1.0g was released. This version corrected some display problems that occured
when changing flow conditions. A blinking banner was also introduced for the
boundary layer separation and compressible flow errors.
On 18 June 09,
version 1.0f was released. This is the first released version
of the program.