Aerodynamic Drag: Turbulent Flow & Exchange of Momentum

[fatlady1ac]

Does turbulent flow create more drag due to the exchange of momentum between the slower moving particles and faster moving particles?

 

[boneh3ad]

Yes. The drag goes up by roughly an order of magnitude when the flow transitions to turbulence.

 

[timthereaper]

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.

 

[boneh3ad]

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.

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.

 

[timthereaper]

I guess I said that last one wrong. I only meant that at supersonic speeds that wave drag appears.

 

[fatlady1ac]

Thanks for all the replies.