What is Aerodynamics | Drag and lift forces

What is Aerodynamics

An automobile is a small object submerged amid vast surrounding of air.

  • The motion of the vehicle takes place through a large mass of either stationary air, or  air in motion.
  • The air exerts force on the auto vehicle.
  •  It is the superstructure (body) of the vehicle which is mainly exposed to the air.
  • An arbitrary shaped body will experience a large air resistance which implies that there is more loss of engines power.
  • Consequently less power will be available to propel the automobile thereby causing less load carrying capacity and slow speed for the same fuel consumption.
  • Thus, there exists a need to profile aerodynamically suitable body.
  • The force exerted by air on a moving auto vehicle had two components, one in the direction of motion and the other in a direction perpendicular to the motion.
  • The force in the direction of motion is called drag F D and that in the perpendicular  direction is known as lift F t, Fig.
Drag and lift forces on body
Drag and lift forces on body

The body profile of an automobile should be such that the lift force F L is zero or  negligible, and then the total force on the body is drag force F D.  The viscosity of air is mainly responsible for drag on the body.

Lift : The aerodynamic resultant force which acts perpendicular to the free stream direction when an airfoil moves through the air

Drag: The aerodynamic resultant force which acts parallel to the free stream direction when an airfoil moves through the air

What is aerodynamic force?

Any force resulting from the interaction of the body of our interest with air/other ideal gases is known as aerodynamic force. 

Classification of aerodynamic forces

There are 2 types of aerodynamic forces-normal & shear forces. 

  • Normal force results from gas pressure (acting normally on the surface) & shear force results from viscosity of the gas (viscous shear stress acts parallel to the surface)
  • Relative to motion of the concerned object, the aerodynamic force is resolved along & perpendicular to the relative motion of the body. Force along the relative motion is called ‘drag force’. Force perpendicular to the relative motion is called ‘lift force’.

Aerodynamics is the field that studies air flows and interactions between air flows and bodies.

More specifically, it is a branch of fluid dynamics, along with hydrodynamics and others. It studies phenomena that occur in an airflow, such as the interaction between two or more flows or the effects of changing some parameters on the flow behavior, as well as phenomena that occur when a body is inserted in an airflow, such as the boundary layer, vortex.

Some fields of study that are included in aerodynamics are:

Aeroacustics;
Unsteady aerodynamics;
Computational aerodynamics;
Experimental aerodynamics;
Compressible aerodynamics;
Aerodynamics is largely applied in projects in aeronautical, aerospace and automotive engineering, but other engineering projects such as (but not limited to) bridges and tall edifications must take it in account too.

Outside engineering, other areas such as architecture, urbanism, biology and weather studies also use aerodynamics to properly analyze phenomena.

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