A wind tunnel is a research tool developed to assist with studying
the effects of air moving over or around solid objects.
It consists of four major sections, the entrance, flow development section,
test section, and diffuser.
The total pressure of an air stream flowing in a duct is sum of the
static or bursting pressure exerted upon the sidewalls of the duct and the impact or
velocity pressure of the moving air.
Through the use of a pitot tube connected differentially to a manometer,
the velocity pressure alone is indicated and the corresponding air velocity determined.
The hot wire is used to measure gas and liquid flow precisely.
The most commonly used wire is a platinum coated tungsten wire.
Because air is transparent it is difficult to directly observe
the air movement itself. Instead, a smoke particulate or a fine mist of liquid is
sprayed into the tunnel just ahead of the device being tested. The particulate is
sufficiently low mass to stay suspended in the air without falling to the floor of
the tunnel, and is light enough to easily move with the airflow.
High-speed turbulence and vortices can be difficult to see directly,
but strobe lights and film cameras or high-speed digital cameras can help to capture
events that are a blur to the naked eye.
With the model mounted on a force balance, one can measure lift, drag, lateral forces, yaw, roll, and pitching moments over a range of angle of attack.