Drag Force at very very high Renolds Number ?

[sunnyguha]

What is the expression for Drag Force at very very High Renolds Number flow (>10^6)
as we know the expression
for drag force between Re1 and Re10^5 = 0.5kpAv^2
but this isn't valid aft 10^5 ..
so ...

 

[boneh3ad]

There isn't any general equation for drag at any value of Reynolds number to be honest. Even the equation you quoted depends on a a coefficient that varies wildly for different environments and geometries.

Let me instead pose this question: what exactly is the situation that you are in? What are the details of the system? How high do you consider "very very high," because 10^6 is actually pretty low for quite a few situations.

 

[sunnyguha]

as in let's take an example for a sphere of radius 0.1 m moking with the speed of 100 m/sec
Renolds = pv/viscosity which gives 10^7

so what wud be the drag force calculating expression for this situation

 

[boneh3ad]

It depends on how accurate you want to be. You could use the old formula for a ballpark estimate, or you could go through the long, complicated process of finding pressure drag including the separated regions and viscous drag. It all depends on what you want.

 

[RandomGuy88]

for drag force between Re1 and Re10^5 = 0.5kpAv^2
but this isn't valid aft 10^5 ..
so ...

Since when is this not valid for Re > 10^5?

As long as you know your drag coefficient this equation is completely valid.