Does water flowing through a pipe make noise?

[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.

 

[anorlunda]

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

 

[member 656954]

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!

 

[DaveC426913]

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.

 

[member 656954]

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.

 

[anorlunda]

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.

 

[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

 

[member 656954]

Send a pig through every few minutes.

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

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!

 

[256bits]

Or you could send an alligator

, rather than a pig, every so often to foil any swimmers coming up the pipe.

 

[member 656954]

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.

 

[DaveC426913]

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]

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.

 

[DEvens]

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.

 

[DaveC426913]

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.

 

[jbriggs444]

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.

 

[stefan r]

The water hammer effect can be extremely loud.

 

[member 656954]

The water hammer effect can be extremely loud.

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

 

[essenmein]

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.

 

[member 656954]

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

 

[DaveC426913]

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.

 

[member 656954]

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