Consider flow through the converging and diverging portions of a tube with varying radius:
[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/ShMQH.png

In inviscid flow, Bernoulli's equation states that velocity at the throat will be the highest, so this area will have the lowest pressure.

**If the flow is viscous and *locally* fully developed throughout, however, then my intuition says that the throat will have the highest pressure. Is this true?**

I reason this is true because the volume flow rate $Q$ must stay constant in an incompressible flow. If the flow is locally fully developed at each point $x$, then the flow rate is:

$$ Q = \frac{\pi R^4}{8 \mu}(\frac{-dP}{dx})$$

As $R(x)$ decreases, then $\frac{-dP}{dx}$ must increase in the algebraic sense. The only way this is possible, and to keep pressure continuity at the throat, is if the pressure distribution has a maximum at the throat.

**Does viscous flow through a nozzle result in an increase in pressure, opposite of what inviscid flow predicts?**