of proposed aircraft and engine components.
During a test, the model is placed in the
of the tunnel and air is made to flow past the model.
In some wind tunnel tests, the
aerodynamic forces on the model are measured.
In some wind tunnel tests, the model is instrumented to provide
about the flow of air around the model.
In some wind tunnel tests, flow visualization techniques are used to
provide diagnostic information about the flow around the model.
The figure shows five flow visualization techniques that are used in
wind tunnel testing;
surface oil flow , and
Tufts and surface oil flow are used to provide information about the
state of the
on the surface, particularly to detect flow separation and re-attachment.
Boundary layer separation is a souce of drag and the cause of
Some engineers try to determine where the external flow is going
by studying the flow along the surface.
A more accurate way to visualize free stream flow is to use smoke or laser sheets.
The assumption is made that the smoke or seed particles for the laser
move exactly with the flow and therefore gives some indication of
how the flow moves around the model.
The schlieren photographic technique is used for flows with a large change in
fluid density. The technique relies on the bending
of light rays across density gradients to produce a photographic image that
locates the gradients. Wind tunnel engineers use the schlieren system to locate
which are very thin regions with high density gradients. The system can also be
used to study combustion.
You can investigate some wind tunnel visualization techniques by using our
interactive tunnel testing applet.
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