Now, suppose, I put a trip wire here, what is the guarantee that the flow here is turbulent? The initial flow here will be turbulent, but because of pressure difference- we have seen there is a relationship between pressure and velocity- because of such pressure differences the velocity may further drop; if the pressure difference is high, pressure is high, then velocity may drop further, if velocity drops, turbulence again may fall because Reynolds number will, local, absolute regional Reynolds number will come down again.