14.1 Role of the Wind Tunnel in Design and Optimisation
287
tunnel at Saint-Cyr-l’École provides the opportunity of simultaneously studying the
effect of drag and noise emitted in the A-pillar region, including the rear mirror strut
(see Sect. 3.3.5). On the other hand, other conditions cannot be studied, for example
braking, as the brakes would generate particles upon heating which would spoil the
aeroacoustic treatment material of the wind tunnel. Other requirements such as rainy
conditions cannot be tested either as the water could damage the balance used to
measure aerodynamic forces.
The wind tunnel is only an approximation of the real conditions encountered on
the road and therefore it must evolve to reproduce similar conditions such as high
turbulence intensity, fluctuating wind, obstacles in the vicinity of the vehicle (lorries,
trees, topology, etc.) These are challenges which will not fail to drive the passion of
future aerodynamicist.
The issues to which aerodynamics are confronted are not limited and are spread
over a large variety of disciplines. Current trends in the environmental impact due
to transportation raise a lot of concerns which is driving the development of greener
aviation and automotive industry. This should mobilise aerodynamicists in the years
to come in three major fields of research, namely flow control, aeroacoustic and
aerodynamic shapes optimisation, elaborated below.
14.2 Flow Control
Aerodynamics is essentially the study of the behaviour of the flow which would
be later controlled or modified for a desired effect on the body moving in air or
static but in moving air. The main objectives of controlling the flow are for the
improvement of performance, increasing comfort and safety of the passengers, the
reduction of unwanted unsteadiness such as vibrations, noise, vortices, splashes and
above all the reduction of fuel consumption. The ability to control the flow relies on
understanding the behaviour of the fluid at a very fundamental level. This involves
advanced numerical calculations and fine experimental analyses based on the most
sophisticated measurement techniques.
In aerodynamics the preferred phenomenon to be controlled are: laminar to turbulent transition, separation, turbulent flows, the interactions between shock wave
and boundary layer, flow induced vibrations and noise.
For an aircraft in cruise the friction drag on the surface represents almost half
of the total drag, therefore its reduction presents an opportunity for larger energy
saving. Skin friction drag reduction can be achieved by maintaining the boundary
layer in a laminar state by delaying the transition phenomenon. This is a complex
flow instability phenomenon where theoretical and experimental research have been
motivated to identify the factors influencing it, namely the ambient disturbances such
as turbulence intensity and noise or the conditions on the surface such as pressure
gradients, surface protuberances, vibration and heating. A laminar boundary layer
can be sustained by tailoring a shape that promotes a favourable pressure gradient
as well as improving the surface quality. Maintenance of a laminar state on the wing
287
tunnel at Saint-Cyr-l’École provides the opportunity of simultaneously studying the
effect of drag and noise emitted in the A-pillar region, including the rear mirror strut
(see Sect. 3.3.5). On the other hand, other conditions cannot be studied, for example
braking, as the brakes would generate particles upon heating which would spoil the
aeroacoustic treatment material of the wind tunnel. Other requirements such as rainy
conditions cannot be tested either as the water could damage the balance used to
measure aerodynamic forces.
The wind tunnel is only an approximation of the real conditions encountered on
the road and therefore it must evolve to reproduce similar conditions such as high
turbulence intensity, fluctuating wind, obstacles in the vicinity of the vehicle (lorries,
trees, topology, etc.) These are challenges which will not fail to drive the passion of
future aerodynamicist.
The issues to which aerodynamics are confronted are not limited and are spread
over a large variety of disciplines. Current trends in the environmental impact due
to transportation raise a lot of concerns which is driving the development of greener
aviation and automotive industry. This should mobilise aerodynamicists in the years
to come in three major fields of research, namely flow control, aeroacoustic and
aerodynamic shapes optimisation, elaborated below.
14.2 Flow Control
Aerodynamics is essentially the study of the behaviour of the flow which would
be later controlled or modified for a desired effect on the body moving in air or
static but in moving air. The main objectives of controlling the flow are for the
improvement of performance, increasing comfort and safety of the passengers, the
reduction of unwanted unsteadiness such as vibrations, noise, vortices, splashes and
above all the reduction of fuel consumption. The ability to control the flow relies on
understanding the behaviour of the fluid at a very fundamental level. This involves
advanced numerical calculations and fine experimental analyses based on the most
sophisticated measurement techniques.
In aerodynamics the preferred phenomenon to be controlled are: laminar to turbulent transition, separation, turbulent flows, the interactions between shock wave
and boundary layer, flow induced vibrations and noise.
For an aircraft in cruise the friction drag on the surface represents almost half
of the total drag, therefore its reduction presents an opportunity for larger energy
saving. Skin friction drag reduction can be achieved by maintaining the boundary
layer in a laminar state by delaying the transition phenomenon. This is a complex
flow instability phenomenon where theoretical and experimental research have been
motivated to identify the factors influencing it, namely the ambient disturbances such
as turbulence intensity and noise or the conditions on the surface such as pressure
gradients, surface protuberances, vibration and heating. A laminar boundary layer
can be sustained by tailoring a shape that promotes a favourable pressure gradient
as well as improving the surface quality. Maintenance of a laminar state on the wing