Chapter 2
Wind Tunnels and Other Aerodynamic
Test Facilities
2.1 Background of Wind Tunnels
2.1.1 Wind Tunnel Principle
The wind tunnel is a means of studying and understanding the behaviour of an aerial
or ground vehicle by performing an experiment, usually on a scaled model. The direct
force measurements (mainly the lift, drag, side force and moments) can be extrapolated to the actual vehicle if dynamic similarities are satisfied. The wind tunnel,
or other means of ground testing, also allows a detailed characterisation of the flow
while measuring the wall pressure, skin friction, velocity and turbulence fields, etc.
Through the implementation of appropriate measurement techniques, these quantities in particular allow very detailed validation of the numerical and analytical methods. The wind tunnel experiment allows the analysis of certain critical phenomena
occurring at extreme conditions, such as massive separation, unsteadiness, buffeting, flutter and many more. These experimental facilities also allow detailed study of
local phenomena that are detrimental for the proper operation or performance of the
overall system. Some of these phenomena are shock-wave/boundary-layer interactions, the development of mixing zones, vortices, laminar to turbulent boundary-layer
transition, and so on.
The wind tunnel static or fixed model test is based on Newton’s principle of
relative velocity formulated as early as 1687, the forces acting on a body immersed
in a fluid flow are the same as the body moving through the fluid at rest or that of
the fluid flows around the static body at the same relative speed. This change of
reference poses a problem when studying ground vehicles on a road or tracks and
aircraft operating close to the ground when taking off or landing. The relative speed
of the vehicle to the ground influences the flow: it is usually known as the ground
effect. Thus, in a wind tunnel where the vehicle is fixed, to reproduce this effect it
is necessary that the floor representing the ground moves at the same speed as the
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_2
27
Wind Tunnels and Other Aerodynamic
Test Facilities
2.1 Background of Wind Tunnels
2.1.1 Wind Tunnel Principle
The wind tunnel is a means of studying and understanding the behaviour of an aerial
or ground vehicle by performing an experiment, usually on a scaled model. The direct
force measurements (mainly the lift, drag, side force and moments) can be extrapolated to the actual vehicle if dynamic similarities are satisfied. The wind tunnel,
or other means of ground testing, also allows a detailed characterisation of the flow
while measuring the wall pressure, skin friction, velocity and turbulence fields, etc.
Through the implementation of appropriate measurement techniques, these quantities in particular allow very detailed validation of the numerical and analytical methods. The wind tunnel experiment allows the analysis of certain critical phenomena
occurring at extreme conditions, such as massive separation, unsteadiness, buffeting, flutter and many more. These experimental facilities also allow detailed study of
local phenomena that are detrimental for the proper operation or performance of the
overall system. Some of these phenomena are shock-wave/boundary-layer interactions, the development of mixing zones, vortices, laminar to turbulent boundary-layer
transition, and so on.
The wind tunnel static or fixed model test is based on Newton’s principle of
relative velocity formulated as early as 1687, the forces acting on a body immersed
in a fluid flow are the same as the body moving through the fluid at rest or that of
the fluid flows around the static body at the same relative speed. This change of
reference poses a problem when studying ground vehicles on a road or tracks and
aircraft operating close to the ground when taking off or landing. The relative speed
of the vehicle to the ground influences the flow: it is usually known as the ground
effect. Thus, in a wind tunnel where the vehicle is fixed, to reproduce this effect it
is necessary that the floor representing the ground moves at the same speed as the
© Springer Nature Switzerland AG 2020
B. Chanetz et al., Experimental Aerodynamics,
Springer Tracts in Mechanical Engineering,
https://doi.org/10.1007/978-3-030-35562-3_2
27