What is Aerodynamics?
Aerodynamics is a very broad subject in aerospace engineering, which generally focuses on the movement of fluid. In aerodynamics, the word, fluid, means liquid or gas. There is no hard and fast definition of aerodynamics, but rather the generalisation that aerodynamicists are fluid flow engineers.
In its most general sense, the word aerodynamics can be decomposed into two parts,
- Aero – meaning air
- Dynamics – relating to the movement of something
Therefore, aerodynamics can be noted most commonly as the study of the movement of air. The motion of solid objects is well known throughout engineering and science. In general, if you apply a force to an object which is solid, it will move against friction at a particular velocity. It will either accelerate, or remain constant, or if the force is removed it will decelerate. In each case, the object shape remains constant. It’s mass and density remain constant.
Air is a fluid, which therefore has much weaker intermolecular bonds than solids. The application of a force to a fluid is completely different to the motion of a solid body. Fluids in the real world twist and distort and move around due to the elasticity of the fluid. This elasticity is known as viscosity – which is a measure of the resistance of a fluid to deformation due to shear or tensile stresses.
In a similar manner to solid body dynamics, equations of motion are derived to describe the behaviour of the dynamics of a fluid. For a Newtonian fluid, the equations which are used are called the Navier-Stokes equations.
The Navier-Stokes Equations – Equations of Motion for a Newtonian Fluid
The motion of a Newtonian fluid is described by the Navier-Stokes equations, which take into consideration the application of three physical conservation laws, namely,
- Conservation of Mass
- Conservation of Momentum
- Conservation of Energy
Their derivation yields five non-linear equations, which are closely coupled together. These equations are,
- 1 equation describing the conservation of mass
- 3 equations describing the conservation of momentum (for a 3D cartesian reference axis)
- 1 equation describing the conservation of energy
It is commonly accepted that collectively, the 5 equations are the Navier-Stokes equations. However, historically, the Navier-Stokes equations are those which describe the conservation of momentum.
Why Study Aerodynamics?
The obvious application of aerodynamics is in aerospace engineering in the design of aircraft. However, aerodynamicists feature in many other jobs. Some examples of aerodynamics jobs would include,
- Designing cooling systems on cars
- Researching underwater currents
- Aeroacoustics modelling
- Propulsion system design
The study of aerodynamics yields a lot of useful information, which can be utilised to improve product design. There are various approaches available to understand aerodynamics,
- Experimental testing of systems using various techniques such as wind-tunnel testing, hot-wire anemometry, laser-dopler-velocimetry, oil flow patterns and Schlieren photography
- Numerical modelling using advanced mathematical models of fluid flow which are solved on super computer clusters
These investigations yield useful information such as surface pressure, the movement of the flow, as well as many physical properties within the flow itself.
Aerodynamics of a Plane
In aircraft aerodynamics, the design engineer is particular interested in knowing the lift and drag coefficients of the aircraft. Nowadays computational fluid dynamics (CFD) is used to model the air flow around a full-size aircraft. The results from the CFD yield surface pressure measurements, which can be integrated with respect to the lift and drag axes.
F1 Aerodynamics
In Formula 1 aerodynamics the main goal is to maximise the downforce on the car, whilst minimising the drag. Traditionally the aerodynamics was investigated in wind tunnels. However, nowadays, the use of CFD is much more prevalent, due to it’s significantly lower cost.
Question: Why did you pursue a career in aerodynamics?