Understanding the Transition to Turbulent Flow in Pipe Systems

[bortonj88]

Hi

As fluid enters a pipe and progresses further down, does the shear stress at the wall reduce whilst the boundary layer increases and viscous forces take over?

Thanks

 

[boneh3ad]

It is a little more complicated. As the boundary layer develops, the shear stress goes down, however, as you get farther down the pipe, the flow will transition to turbulence, at which point the shear stress jumps through the roof again and, while it does decrease somewhat after that, it is typically higher than at any point while the flow was still laminar. In other words, if you plotted $\tau_w$ vs. $x$, there would be a discontinuity at the point where the flow transitions. This assumes you have a high enough Reynolds number to go turbulent of course.