Ground simulation addresses a number
of phenomena experienced by objects that move on or near the ground.
The presence of the ground has an important impact on the flow behavior
over the object. Dependent on the distance with respect to the ground,
the generated air circulation around the object is influenced. Whereas
in reality the object moves in relation to the air and the ground, this
is reversed in the wind tunnel where the wind moves in relation to the
object and the floor. Consequently, a boundary layer is developed along
the tunnel floor (and the other tunnel walls), which is not
representative for the real situation. For good ground simulation the
following aspects are therefore of prime importance:
- the boundary layer on the tunnel floor
- movement of the object in relation to the tunnel floor
To minimize the effects of the floor
boundary layer, DNW uses a ground plane mounted on the tunnel floor in
combination with an integrated scoop system. The movement of the ground
can be simulated by a moving belt system that is integrated in the
ground plane. Moving belt systems are also often referred to as rolling
road systems.
Boundary layer
In ground simulation testing, the
effects of the floor boundary layer must be eliminated such that it
does not interfere with the flow around the test object. The thickness
of the boundary layer in the wind tunnel varies and depends on the
location and the wind speed; the layer is thicker for lower wind speeds
and grows with distance.
One of the techniques used to reduce
the thickness of the boundary layer is the use of a grond plane below
the object. The ground plane is mounted at the same distance to the
tunnel floor and is often used in combination with an integrated
special scoop system. This system scoops away the boundary layer that
was built-up on the tunnel floor. A new, much thinner boundary layer
will build-up on the ground plane.
The thickness of the tunnel floor
boundary layer can also be reduced by tangential blowing. This is done
by means of high pressure air blown along the floor of the tunnel, such
that the boundary layer in the area close to the test object is
minimized.
Moving belt ground plane
The moving belt ground plane
involves a technique specially developed by DNW. The plane consists of
a belt that moves at wind speed. The moving belt is fully integrated in
the above mentioned ground plane/scoop system. The moving belt ground
plane technique is of special importance in conducting tests on the
landing and take-off of aircraft. The moving belt is also used for
measurements of aerodynamic effects experienced on ground vehicles.
DNW’s development of the moving belt
ground plane is rather unique and has resulted in a belt system that
can move up to high wind speeds.