Tau.Neutrino said:
oroville dam spillway
Why don’t they use laminar flow pipes set further back to minimize the turbulence and reduce damage?
What is laminar and turbulent flow?
Laminar flow is a flow regime characterized by high momentum diffusion and low momentum convection. When a fluid is flowing through a closed channel such as a pipe or between two flat plates, either of two types of flow may occur depending on the velocity and viscosity of the fluid: laminar flow or turbulent flow.
The transition from laminar flow to turbulent flow is governed by Reynolds number, which is V*d*rho/mu. There’s no changing rho and mu. As the size of your object (d) increases, the Reynolds number increases, and the flow transitions from being laminar to being turbulent. Dam spillways are big, large d, turbulent flow.
The shallow depth of water on the spillway helps to keep the Reynolds number down as low as possible, which is not very low, particularly in flood times. The curved shape of the upper spillway profile is designed to keep a small amount of positive pressure on curved concrete. The concrete blocks 3/4 of the way down the spillway are there to induce massive turbulence into the flow because that turbulence is the most efficient way to dissipate energy.
From the pattern of damage here, it is clear that the water pressure on top of the concrete in to upper part of the spillway has become negative (lower than atmospheric) which has sucked up blocks of concrete from the upper part of the spillway. So the engineers need to rethink their profile of curvature to stop that from happening again, or divert the water somewhere else (in a place that doesn’t undermine the dam wall).