are designed for a specific purpose and
Therefore, there are many different
types of wind tunnels
and several different ways to classify wind tunnels.
In this section of the website we shall
present various types of wind tunnels and discuss some of the unique features
of each type of tunnel.
On the figure, we show a schematic drawing of an open return wind tunnel.
This type of tunnnel is also called an Eiffel tunnel, after the French engineer,
or an NPL tunnel , after the National Physical Laboratory in England, where the tunnel
was first used. The Eiffel tunnel has an open test section, while the NPL tunnel has a
closed test section as shown in the figure.
Wright Brother's wind tunnel
was an open return design.
In the open return tunnel, the air that passes through the
is gathered from the room in which the tunnel is located. The arrows on the figure
denote the flow of air through the wind tunnel and around the room.
The other major type of wind tunnel is the
closed return tunnel, in which the air is conducted from
the exit of the fan to the contraction section by a series of ducts and turning vanes.
The open return tunnel has some advantages and some disadvantages relative to the closed
Advantages of the Open Return Tunnel
Low construction cost.
Superior design for propulsion and smoke visualization. There is no accumulation
of exhaust products in an open tunnel.
Disadvantages of the Open Return Tunnel
Poor flow quality possible in the test section. Flow turning the corner into the bellmouth
may require extensive screens or flow straighteners. The tunnel should also be kept away
from objects in the room (walls, desks, people ...)that produce asymmetries to the bellmouth.
Tunnels open to the atmosphere are also affected by winds and weather.
High operating costs. The fan must continually accelerate flow through the tunnel.
Noisy operation. Loud noise from the fan may limit times of operation.
Here is a Java program that you can use to study the operation of an open return wind tunnel.
You can also use this software for the prelimiinary design of a low speed, open return tunnel
You can change values of the input parameters by typing into the input boxes or
clicking and dragging the slider bars.
This program solves the conservation of
for one dimensional ideal flow conditions. The analysis is only valid for
low-speed operation in which the air density remains a constant.
Details of the software are described on a
You can download your own copy of the program to run off-line by clicking on this button: