Does water flowing through a pipe make noise?

  • Thread starter Tghu Verd
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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.
 
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How about them simply breaking an infrared light beam. Like the sensor on your automatic garage door opener.
 
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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

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

1572693157477.png
 

jim mcnamara

Mentor
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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.
 

256bits

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Or you could send an alligator
nailbiting[1].png
, rather than a pig, every so often to foil any swimmers coming up the pipe.
 
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Or you could send an alligator
nailbiting[1].png
nailbiting[1].png
, 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

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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. :eek:
 

DEvens

Education Advisor
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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

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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.
 

stefan r

Science Advisor
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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.
 

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