Drag and velocity (magnitude)

[es335]

When is there a 1. order relationship between velocity and drag, and when is it 2. order? And why is there a difference, and why 1. and 2. order and not 3. or 4. ?

I know that when the velocity is low the relationship is 1. order and when the velocity is high it becomes 2. order. But I don’t know where the limit is.

Can anyone help?

Cheers.

 

[hacksaw]

drag =kv is the viscous drag limit
drag =kv^2 is the turbulent limit.

the change in exponent has to do with what happens in the boundary layer. golf balls take advantage of this by dimpling and effectively reduce the drag.

 

[es335]

Thanks. Do you know what happens in the boundary layer?
And do you know why the laminar flow is dependent in the first order? (and why the turbulent in the second order?).


And, as I have understood it, the reason of using dimples in the golf ball is because this introduces/insures turbulent flow which is capable of handling large pressure gradients, thereby avoiding separating (= large drag) in contrary to laminar flow which will separate at high pressure gradients.