Chapter 1
The Experimental Approach
in Aerodynamic Design
1.1 Aerodynamics, What for?
Aerodynamics is the study of the flow of air around bodies, generally an aerial or
ground vehicle, but also structures, turbomachine blades and rotors, wind turbines,
or in more diverse cases such as bikes and other sports equipments. Indeed, any fluid
in contact with a solid surface exerts a normal and tangential pressures, the integral
effect of this pressure over the whole body generates a resultant force referred as the
aerodynamic force. This resultant force is applied at a point known as the centre of
pressure, which as a rule of thumb does not coincide with the centre of gravity of the
body where the weight is exerted. The presence of these two points of action of the
force induces an aerodynamic moment tending to rotate the body around its centre of
gravity. A main goal in aerodynamics is to determine the components of this resultant
force and their moments, the whole constituting the aerodynamic forces.
The aerodynamic resultant force is decomposed according to a system of axes
linked to the relative direction of flight of the vehicle: the force can be decomposed
into other components, the drag force which acts in the direction opposing the motion
of the vehicle which must be compensated either by a propulsion unit (see Fig. 1.1),
or a component of the weight in the opposite direction for example in the case of
gliders.
Drag is the component that contributes to most of the energy consumption for
propulsion. The component almost normal to the direction of flight or the oncoming
wind is the lift. It requires very little or no energy at all and is used to compensate
for weight and manoeuvres. A large majority of aerial and ground vehicles have a
plane of symmetry, usually vertical in nominal operation. We can then break down
the aerodynamic forces in this plane of symmetry, with the lift and drag lying on
this plane and, the third component, perpendicular to the plane of symmetry of the
vehicle, called the side force. It therefore defines the load carrying capacity of the
aircraft referred as the payload (number of passengers, cargo mass). For automotive
applications, the bump effect of the vehicle on the road could create lift, but this
© 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_1
1
The Experimental Approach
in Aerodynamic Design
1.1 Aerodynamics, What for?
Aerodynamics is the study of the flow of air around bodies, generally an aerial or
ground vehicle, but also structures, turbomachine blades and rotors, wind turbines,
or in more diverse cases such as bikes and other sports equipments. Indeed, any fluid
in contact with a solid surface exerts a normal and tangential pressures, the integral
effect of this pressure over the whole body generates a resultant force referred as the
aerodynamic force. This resultant force is applied at a point known as the centre of
pressure, which as a rule of thumb does not coincide with the centre of gravity of the
body where the weight is exerted. The presence of these two points of action of the
force induces an aerodynamic moment tending to rotate the body around its centre of
gravity. A main goal in aerodynamics is to determine the components of this resultant
force and their moments, the whole constituting the aerodynamic forces.
The aerodynamic resultant force is decomposed according to a system of axes
linked to the relative direction of flight of the vehicle: the force can be decomposed
into other components, the drag force which acts in the direction opposing the motion
of the vehicle which must be compensated either by a propulsion unit (see Fig. 1.1),
or a component of the weight in the opposite direction for example in the case of
gliders.
Drag is the component that contributes to most of the energy consumption for
propulsion. The component almost normal to the direction of flight or the oncoming
wind is the lift. It requires very little or no energy at all and is used to compensate
for weight and manoeuvres. A large majority of aerial and ground vehicles have a
plane of symmetry, usually vertical in nominal operation. We can then break down
the aerodynamic forces in this plane of symmetry, with the lift and drag lying on
this plane and, the third component, perpendicular to the plane of symmetry of the
vehicle, called the side force. It therefore defines the load carrying capacity of the
aircraft referred as the payload (number of passengers, cargo mass). For automotive
applications, the bump effect of the vehicle on the road could create lift, but this
© 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_1
1