I don’t mean banging or any unusual noises, I’m just talking about the usual noise of flowing water. What about the process of water flowing through pipes actually causes that sound? Raindrops make a sound because they’re hitting the ground, but water flowing through a pipe isn’t hitting anything…is it?
In: Physics
Answer: It is hitting the sides of the pipe. There is a friction between the water and the interior surfaces of the pipe.
Laminar flow in a pipe makes almost no noise, as you would expect. Laminar flow is when the layers of water (inner and outer) in the pipe all move by themsleves without mixing. Hence the name laminar, like the word laminated. It means layered. Inner layer moves a lot quicker, outer layer near pipe walls actually barely even moves up to a “scouring” velocity.
Turbulent flow has water swirling around, and this will make noise. Turbulent flow can be caused by elbows, valves, pipe size reduction, and other barriers that obstruct the straight laminar flow. However, if the speed of the water is high enough it will cause turbulent flow even in a straight pipe section. The water has friction with the pipe walls and with itself between areas traveling at different speeds. Up until a certain speed, water is viscous enough to avoid the turbulence. Something more vicious (honey is very viscous) would see turbulent flow way earlier.
You can see the same effect in a river. Laminar flow will be clear and silent. Turbulent flow will be noisy and white. Turbulent flow in a river is either caused by obstructions or very fast flow, just like in a pipe.
In most sewer and drainage systems, there’s an air gap above the water within the pipe. Depending on what the pipe is used for, you can hear as water hits the inside of the pipe or turbulence at the surface of a constant flow. These sounds bounce around the air gap inside the pipe and can be heard outside of it.
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