Aerodynamic Drag: Turbulent Flow & Exchange of Momentum

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In summary, turbulence creates more drag due to the exchange of momentum between the slower moving particles and faster moving particles.
  • #1
fatlady1ac
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Does turbulent flow create more drag due to the exchange of momentum between the slower moving particles and faster moving particles?
 
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  • #2
Yes. The drag goes up by roughly an order of magnitude when the flow transitions to turbulence.
 
  • #3
From what I understand, there are multiple types of drag that come into play with turbulent flow. Friction drag arises due to the viscous effects of the fluid. Since the turbulent flow profile has such a large change from the free stream velocity to zero over a very short distance (du/dy is large), it causes a larger friction drag than would a laminar flow profile. Pressure drag is created by a pressure difference due mainly to the shape of a body and how the flow profile changes over the shape of the body. If the flow over the body at any point is turbulent enough to considered supersonic, you get wave drag.
 
  • #4
timthereaper said:
From what I understand, there are multiple types of drag that come into play with turbulent flow. Friction drag arises due to the viscous effects of the fluid. Since the turbulent flow profile has such a large change from the free stream velocity to zero over a very short distance (du/dy is large), it causes a larger friction drag than would a laminar flow profile.

This is true, and is the physical reason the drag is greater.

timthereaper said:
Pressure drag is created by a pressure difference due mainly to the shape of a body and how the flow profile changes over the shape of the body. If the flow over the body at any point is turbulent enough to considered supersonic, you get wave drag.

Pressure drag (or form drag) remains the same regardless of whether the ball is laminar or turbulent. The only real exception is when a boundary layer is turbulent which prevents it from separating (as in a golf ball) in which case the form drag actually decreases. However, this is not a direct result of turbulence, but a secondary result due to a turbulent boundary layer's tendency to remain attached.

The concepts of turbulence and supersonic flow are disjoint and have nothing to do with one another. Wave drag has nothing to do with turbulence and turbulence will not do anything to change the amount of wave drag you get on a supersonic vehicle.
 
  • #5
I guess I said that last one wrong. I only meant that at supersonic speeds that wave drag appears.
 
  • #6
Thanks for all the replies.
 

What is aerodynamic drag?

Aerodynamic drag is the force that acts upon an object as it moves through a fluid, such as air. It is caused by the friction and pressure differences between the object and the surrounding fluid, and it is typically measured in units of force per unit area, such as pounds per square inch.

How is turbulent flow different from laminar flow?

Turbulent flow is characterized by chaotic and irregular movement of the fluid particles, while laminar flow is smooth and orderly. Turbulent flow can create more drag than laminar flow, as it causes more mixing and mixing leads to a greater exchange of momentum between the object and the fluid.

What factors affect the amount of aerodynamic drag an object experiences?

The shape, size, and velocity of the object, as well as the properties of the fluid it is moving through, all play a role in determining the amount of aerodynamic drag an object experiences. Additionally, the presence of obstacles or rough surfaces in the fluid can also impact the amount of drag.

How does the exchange of momentum between an object and the surrounding fluid affect aerodynamic drag?

The exchange of momentum between the object and the fluid is what ultimately causes aerodynamic drag. As the fluid particles interact with the object, they exchange momentum, resulting in a force acting in the opposite direction of the object's motion. The more momentum that is exchanged, the greater the aerodynamic drag.

What are some ways to reduce aerodynamic drag?

One way to reduce aerodynamic drag is to streamline the shape of the object, reducing its surface area and creating a more laminar flow. Additionally, using smooth and aerodynamic materials and minimizing obstacles in the fluid can also help to reduce drag. Another method is to increase the velocity of the object, as this can result in a thinner boundary layer and less turbulent flow.

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