1.1 Aerodynamics, What for?
3
Fig. 1.2 Sources of noise on a transport aircraft (© LMFA)
noise beyond speeds of 300 km/h for trains and 120 km/h for cars. For aircraft,
during the approach phase, whilst the engines are at low speed, the aerodynamic
noise tends to become predominant, in particular that generated by landing gears.
Figure 1.2 shows the main sources of noise on a transport aircraft. Convective and/or
radiative heat transfer between the flow and the wall falls in the aerothermal or
aerothermodynamic field. These aspects play an essential role in hypersonic flight
where the vehicle is subjected to intense heating during a re-entry into the atmosphere.
Conversely, a flow can be used to cool hot parts such as in a radiator or heat exchanger.
In military applications, the reflection of electromagnetic waves and the infrared
radiation of fuselages and jet engines of combat aircraft and helicopter are used to
detect their presence and lock them as target for or by guided missiles. Stealth, that is
to say the ability of a combat vehicle to escape these means of detection, imposes very
specific shapes, which forces us to reconsider their aerodynamics (Fig. 1.3 shows an
image of a combat drone or UCAV).
The impact of aerodynamics is also considerable in the quest for energy savings,
which would help the reduction of noxious gas emission otherwise affecting our
environment, or simply the noise when the vehicle passes by. This encourages the
design of optimised vehicles while focusing on reducing the drag in particular.
It is very useful to define non-dimensional aerodynamic coefficients which are
the aerodynamic forces normalised by the product of the dynamic pressure of the
freestream flow (1/2 ρV
2 ) and the reference area of the vehicle. For an aircraft this
reference surface is generally the planform area of the wing. For a land vehicle
or a bluff body, the frontal area is used instead. By way of illustration, Table 1.1
gives the coefficients of drag (C D ), lift (C L ) and the lift-to-drag ratio (L/D) which
3
Fig. 1.2 Sources of noise on a transport aircraft (© LMFA)
noise beyond speeds of 300 km/h for trains and 120 km/h for cars. For aircraft,
during the approach phase, whilst the engines are at low speed, the aerodynamic
noise tends to become predominant, in particular that generated by landing gears.
Figure 1.2 shows the main sources of noise on a transport aircraft. Convective and/or
radiative heat transfer between the flow and the wall falls in the aerothermal or
aerothermodynamic field. These aspects play an essential role in hypersonic flight
where the vehicle is subjected to intense heating during a re-entry into the atmosphere.
Conversely, a flow can be used to cool hot parts such as in a radiator or heat exchanger.
In military applications, the reflection of electromagnetic waves and the infrared
radiation of fuselages and jet engines of combat aircraft and helicopter are used to
detect their presence and lock them as target for or by guided missiles. Stealth, that is
to say the ability of a combat vehicle to escape these means of detection, imposes very
specific shapes, which forces us to reconsider their aerodynamics (Fig. 1.3 shows an
image of a combat drone or UCAV).
The impact of aerodynamics is also considerable in the quest for energy savings,
which would help the reduction of noxious gas emission otherwise affecting our
environment, or simply the noise when the vehicle passes by. This encourages the
design of optimised vehicles while focusing on reducing the drag in particular.
It is very useful to define non-dimensional aerodynamic coefficients which are
the aerodynamic forces normalised by the product of the dynamic pressure of the
freestream flow (1/2 ρV
2 ) and the reference area of the vehicle. For an aircraft this
reference surface is generally the planform area of the wing. For a land vehicle
or a bluff body, the frontal area is used instead. By way of illustration, Table 1.1
gives the coefficients of drag (C D ), lift (C L ) and the lift-to-drag ratio (L/D) which