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Drag Force - Aerodynamics Force Resolution
Updated: Jul 21, 2021
What are different types of Drag Force? How to reduce its effect?
Table of Contents
No one likes to be dragged or bogged down by anyone. Why should the vehicles tolerate it either? Haha!!
We already have written about Aerodynamic force and Lift force here. So understanding Drag force would be easy. Without any further delay, let's get into the topic!
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Drag Force
Drag Force is a component of Aerodynamic Force. Drag force is not desirable as it literally drags down the object, and reduces its speed.
Drag Force is generated due to the friction between the fluid and a solid body having a relative velocity.
The drag coefficient is different for different shapes. The drag coefficient is determined experimentally. It mainly depends on the frontal area and the disturbance of the fluid flow due to the presence of that shape. The more disturbance, the more is the drag coefficient.
The area that is considered in this formula can either be the frontal area, wing area, or the total surface area.
Factors affecting Drag Force
The factors affecting Drag Force are very similar to factors affecting Aerodynamic Force as it is a component of Aerodynamic Force.
Shape and size of the object: As the geometry and the roughness of the object change, the drag force associated with it also changes.
Velocity and direction of flow: In the above formula itself, one can see as velocity increases, the drag force also increases. The inclination of the object with respect to the direction of flowing fluid plays an important role. If inclination changes, the projected area changes, hence the direction of flow also changes.
Mass, viscosity, and compressibility of air: If these change, the drag force also changes.
Types of Drag Forces
Induced Drag Force
Induced drag is formed due to the lift force. As soon as lift force comes into the picture, induced drag is generated. At the end of the wing, wingtips are present. These wingtips generate turbulence due to lower pressure above the wing and higher pressure below the wing giving rise to tip vortex. This drag force not only affects the aircraft's speed but also causes turbulence in the aircraft which are traveling behind them, depending on their size.
Parasite Drag Force
Parasite Drag is the drag generated independently of lift force. It comprises Interference and Profile Drag.
Interference Drag Force
Interference drag is formed due to the presence of some structure that is not aerodynamically designed or is present to support the aerodynamic structure.
Profile Drag Force
Profile drag is made up of Skin friction and Pressure drag force. As the name suggests, this drag depends on the profile (shape, size, etc.) of the vehicle.
Skin Friction Drag Force or Friction Drag Force
Skin Friction drag can be understood easily at the molecular level. When the molecules of the fluid and the solid come in contact with each other, friction is produced. This friction creates drag and the velocity of the vehicle reduces. It is directly proportional to the area of the vehicle and applied all over the body. The friction drag is less when the flow is laminar and more when the flow is turbulent.
Pressure Drag Force or Form Drag Force
Pressure drag is formed due to the shape of the vehicle. Pressure drag is dependant on the frontal area. As the frontal area decreases the pressure drag also decreases. It also depends on the surface roughness, thickness, etc. In winters, due to the formation of ice on the aircraft wings, drag force is so high, that it may not be able to lift itself.
It should be noted that as velocity increases, parasitic drag also increases, but induced drag decreases.
Base Drag Force
Base drag is formed at the base or end of the vehicle. At the end of the vehicle, a wake is formed due to turbulence.
Wave Drag Force and Ram Drag Force
Wave drag is formed at high speeds such as supersonic speeds. Ram drag is produced when free stream air is brought inside the craft. For example, jet engines mix air and fuel to burn it, which creates ram drag or negative thrust.
How to reduce the effect of Drag?
There are many different ways to reduce the effect of drag depending on the object and which drag one wants to reduce from above.
Making sure the fluid flow is laminar around the object, or there is no boundary layer separation.
Adjust its velocity such that drag force is reduced.
Adjust the surface roughness such that the drag force is reduced.
Reducing its surface area
By designing the body streamlined.
History on Drag Force
The presence of Drag was known since Aristotle (Greek philosopher, around 350BC). Mervyn O'Gorman (British electrical and aircraft engineer) termed the word drag in 1913 over the word drift coined by Archibald Reith Low (British pilot and aeronautics pioneer). Louis Charles Breguet (French aircraft designer and builder) in 1922 started to make efforts on reducing drag and became very successful in building the aircraft accordingly. Then Ludwig Prandtl (German fluid dynamicist, physicist, and aerospace scientist) came up with a boundary layer in the 1920s to reduce skin friction. In 1929, Melvill Jones (Francis Mond Professor of Aeronautical Engineering at the University of Cambridge) presented the paper ‘The Streamline Airplane’ which provided streamlining of an aircraft for reducing the drag effect.
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Summary
Drag Force is generated due to the friction between the fluid and a solid body having a relative velocity.
Drag force coefficient depends on the shape and size of the object and is found out experimentally.
The factors affecting Drag Force are Shape and size of the object, velocity and direction of flow, and Mass, viscosity, and compressibility of air.
Induced drag is drag due to the lift force and the parasitic drag is independent of lift force.
As velocity increases, parasitic drag also increases, but induced drag decreases.
Drag force is undesirable hence different solutions are applied to reduce the drag force on different objects. It also depends on which type of drag force one wants to reduce.
There would be no drag force in absence of any fluid around the object.
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