# Does water flowing through a pipe make noise?

• member 656954
As far as flowing water making noise, noise is vibration, so any eddies/turbulence etc would make noise. Is the flow turbulent? (there is math to do here, basically calculate the Reynolds number of the flow you have proposed).In summary, the conversation discusses the use of an incursion team entering a 10-foot diameter water outlet pipe using electric sleds for propulsion. The team wonders about sensors detecting them and the noise level in the pipe, which has a flow rate of 3.18086e+07 l/h with a 1.25 m/s current. It is determined that the water flow could potentially make noise due to turbulence and cavitation, and measures must be taken to mask the noise of the
member 656954
I've my small incursion team entering a 10 foot diameter water outlet pipe using electric sleds for propulsion and was wondering about sensors in the pipe detecting them.

They're wearing suits that mask their IR, but what about noise? The pipe flow is 3.18086e+07 l/h with a 1.25 m/s current, and I assumed the water flow won't make any noise itself as it's entirely filling the pipe.

Is that right? Or does water flowing through a pipe make a discernible noise within the pipe? The type of noise that would mask electric sleds.

How about them simply breaking an infrared light beam. Like the sensor on your automatic garage door opener.

I'm thinking about the sensor system, as the pipe builders were a paranoid bunch, and simple is undoubtedly best, so IR beams - or even just CCTV - is likely. There are ways to combat that, of course, but it was noise I was particularly interested in. Would the team sled along in silence, or would the moving water make noise? And if so, a constant amount or a variable amount?

Gads, it's always the little questions that catch me out when I'm writing and slow down the narrative flow!

A truly paranoid builder might manifold one 10 foot pipe into 100 one foot pipes for a dozen metres...
Ain't nobody going to be sneakin' past that.

Yeah, there are restricted segments a bit further along the story arc. But the pipe is part of a water inlet / outlet system for a large - and secret - underground base 50-ish miles from the ocean, so the constrictions occur way closer to the main infrastructure.

Oil pipelines use "pigs". That is a device that travels through the pipe to clean and/or inspect the inner walls. It occurs to me that it would also do a good job of flushing out any creatures trying to swim upstream. Send a pig through every few minutes.

Bystander and jim mcnamara
Short answer: yes, flowing can make noise, probably not the way you expect.

Consider cavitation as a noise source. Happens from propellers rotating, general flow around sharp corners. Rebreather/scuba make noise, too.
https://en.wikipedia.org/wiki/Cavitation

anorlunda said:
Send a pig through every few minutes.

Oh, I like that idea, consider it appropriated, @anorlunda

jim mcnamara said:
Short answer: yes, flowing can make noise, probably not the way you expect.

Definitely not in the way I expected, @jim mcnamara, thanks for that!

Or you could send an alligator
, rather than a pig, every so often to foil any swimmers coming up the pipe.

256bits said:
Or you could send an alligator
, rather than a pig, every so often to foil any swimmers coming up the pipe.

LOL, that's not quite the vibe I'm looking for, @256bits, but thanks for the suggestion.

256bits
anorlunda said:
Send a pig through every few minutes.

View attachment 252196

OK, that device looks a lot like a jet turbine.

Coupled with the blurb "Send a pig through every few minutes", I had a vision of a gratuitously gory solution to the OP's problem.

anorlunda
DaveC426913 said:
OK, that device looks a lot like a jet turbine
It does look like that , but it is just pushed along by the liquid bring plumped.

DaveC426913 said:
OK, that device looks a lot like a jet turbine.

Looks like wheels on the end of struts, not turbine blades. Wheels like off the bottom of an office chair. Turbine blades would be angled somehow, not just straight. Presumably it's designed to push off the walls on those wheels when it navigates bends and such. When it's just flowing along it presumably is fairly close to neutrally buoyant.

DEvens said:
Looks like wheels on the end of struts, not turbine blades.
Yes.

I didn't say "Ah. Hmm. Upon careful scrutiny, this turbine appears to be made of turbine".

The instant image, coupled with the phrase "Send a pig through it" provoked a fast and visceral reaction.

DaveC426913 said:
The instant image, coupled with the phrase "Send a pig through it" provoked a fast and visceral reaction.
So that's how they make hot dogs.

jim mcnamara, Bystander and anorlunda
stefan r said:
The water hammer effect can be extremely loud.

Excellent, thanks @stefan r , I can definitely use this!

As far as flowing water making noise, noise is vibration, so any eddies/turbulence etc would make noise. Is the flow turbulent? (there is math to do here, basically calculate the Reynolds number of the flow you have proposed).

Regarding the noise of your sleds and the drivers, water is very good at transmitting sound due to its lack of compressibility. So your sleds would be subject to the same issues faced by submarine designers today. So anything like engine sounds, electric or other wise, any vibration source must be isolated from the hull. Even the divers heart beat or breathing could be picked up with sufficiently sensitive equipment.

This water outlet better be gravity fed, any pump that size would make short work of your incursion team lol.

Thanks @essenmein, I have been thinking about the noise issue, I'll need to make the water flow turbulent to cover that off, which is possible with the plot. And the gravity fed question is good. My novel is set early next century so I have leeway with the engineering, but it's also set in a real location so I'm now looking at topological maps as that triggers some interesting thoughts for this sequence.

And speaking of engineering, I see my post has been moved from the Sci-Fi Writing forum to the General Engineering forum, which may make my opening post seem entirely off-topic to new viewers

Tghu Verd said:
Thanks @essenmein, I have been thinking about the noise issue, I'll need to make the water flow turbulent to cover that off,
There's nothing says a outflow pipe has to be full to the roof with water. Even a small height of air should make for noisy flow. Or filled with bubbles from having fallen down a sluice.

DaveC426913 said:
There's nothing says a outflow pipe has to be full to the roof with water.

Thanks @DaveC426913, I'd initially imagined the pipe full, hence my question about noise in the flow.

As with many of my ideas while writing, this started as a thought bubble that quickly expanded beyond the limits of my knowledge and quick google searches. I try for hard-ish science fiction when I write (there's a wormhole and genetically augmented soldiers, so it's not titanium hard) and the generosity of the PF community allows me to at least get the basics right, and know when I've stepped entirely off the path

berkeman

## 1. Does the size of the pipe affect the noise of water flow?

Yes, the size of the pipe can affect the noise of water flow. A larger pipe diameter will allow for smoother and quieter water flow, while a smaller pipe diameter can create turbulence and result in louder noise.

## 2. Why does water flowing through a pipe make noise?

Water flowing through a pipe can make noise due to the movement and turbulence of the water. As the water travels through the pipe, it may encounter obstructions or changes in direction, causing vibrations and resulting in noise.

## 3. Can the material of the pipe impact the noise of water flow?

Yes, the material of the pipe can impact the noise of water flow. Different materials have different density and sound transmission properties, which can affect how much noise is produced as water flows through the pipe.

## 4. Does the water pressure affect the noise of water flow?

Yes, the water pressure can affect the noise of water flow. Higher water pressure can create more force and turbulence, resulting in louder noise. Lower water pressure may produce quieter water flow.

## 5. Is there a way to reduce the noise of water flowing through a pipe?

Yes, there are ways to reduce the noise of water flowing through a pipe. Installing insulation or soundproofing materials around the pipe can help absorb the noise. Additionally, using larger diameter pipes and reducing water pressure can also help decrease the noise level.

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