Originally Posted by
razo125
Ah this adds more confusion actually hehe. I think google led me to the wrong or different formula.
http://ocw.mit.edu/courses/mechanica...bulentFlow.pdf
This formula shows D (hole diameter) as the numerator.
The formula you shared has the D (hole diameter) as the denominator, so we would get opposite results depending on which formula is correct.
I did more digging and I see both examples so I'm not sure which is the right one to apply for our application.
Sorry to be confusing... Google is correct, and yes, the hole diameter is in the numerator.... BUT... When you are substituting the velocity based on the flow difference between the piston velocity and the velocity of the oil in the hole, the diameter of the hole itself ends up in the denominator.
The key equation that is missing is the conservation of flow. Qp=n*Qh, where Q1 = Vp*Ap and Q2 = Vh*Ah. (Ah=pi/4*Dh^2) Since the Re formula needs the velocity of the oil through the hole (Vh), you must rearrange the flow formula for Vh. It ends up being:
Vh = (Vp*Ap)/(Ah*n).... and that is how the diameter of the hole ends up in the denominator. The Diameter of the piston is just used because you know the velocity of the shock and you are using that flow ratio to calculate the flow velocity through the hole.
I hope that's a little clearer???