Let's say I have a free jet of air leaving a pipe into the atmosphere. I know that the static gauge pressure at the pipe exit is equal to the atmospheric. But what about the static gauge pressure 10 meters away if the air is still traveling as a free jet? Is it still atmospheric?
I'm confused. Bernoulli's eqn. says the static pressure inside the jet should be less than atmospheric. As you go further out and the jet slows down, then it should approach atmospheric pressure. The pressure gradient between the atmosphere outside and the low pressure inside the jet leads to air getting sucked into the jet (entrainment).