gas whistling while passing 1

[PaulLag]

Hi there !

hope someboby can help me.
I have a problem with some gas flowing in an header.
The gas flowing in the header is generating a whistle

I was wondering: is there a formula relating gas velocity to the whistle ?
May this whistle be related to tube diameter, too ?
May this be related to tube lenght ?

One important detail is this: the gas comes into this tube from a bigger tube, having a section that is 4 times bigger than the same tube.
The ratio of the two diameters is 2.

many thanks !

 

[PaulLag]

sorry I'd like to add following piece of information:

I calculated the gas velocity, that is 45 m/s
this means we have a Mach number of 0.13.

Thanks for your help

 

[zdas04]

At that speed you are very safe using incompressible flow equations. Flow noise can be caused by any number of things. Think about a wind instrument where you get a huge range of sounds with pretty low velocity from the performer's exhalation. A tuba gives you different sounds than a flute does.

Your whistling could be piping configuration (two elbows out of plane sets up some interesting flow patterns that make noise) or a (planed or unplanned) restriction in the pipe, or gas blowing over a dead leg. I haven't seen a simple step down in diameter turn a quiet system into a noisy system, but don't see anything that would prevent it.

The only field of science that is less well defined than fluid mechanics that I know of is acoustics. I would be really shocked if you came across a reference from piping configuration or fluid velocity to sound frequency.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist

 

[hacksaw]

If you layout the piping configuation with dimensions and the fluid data you might find more specific answers. It is a routine problem covered in most piping accoustic handbooks.

 

[katmar]

45 m/s is towards the upper end of recommended velocities for gases. Norsok P-001 gives the recommendation for limiting gas velocities for noise to 175 / (density^0.43) where the velocity is in m/s and density in kg/m3. But they do not give their criterion for "excessive noise". Allowable noise is likely to be rather different on an offshore rig from a domestic or office situation.

I'm sure you are not looking for a single cut-off point. You need to know at what velocities the noise increases from silent, to a whisper, to a whistle, a scream and finally a roar. In a typical HVAC handbook I found the recommendation that air conditioning duct velocities should be kept below 7 m/s in domestic and office environments. This should give you an indication of when the "whisper" point is reached.

Some very useful recommendations for water velocities in various environments were given by DRWeig in thread378-348061

The size reduction is also a likely source of noise. When a fluid flows through a standard pipe reducer (big to small direction) the fluid continues to converge after the narrowest point in the pipe forming the "vena contracta" where the local velocity could easily be double the calculated average. After the vena contract you have all sorts of eddies and turbulence which could also initiate your whistle. Replacing a pipe reducer with a very slowly converging conical taper may help the situation, but I suspect that your 45 m/s is too high anyway.

Katmar Software - AioFlo Pipe Hydraulics

http://katmarsoftware.com

"An undefined problem has an infinite number of solutions"

 

[PaulLag]

@ mr hacksaw
I am here attaching you the description of the tubes, with velocities and dimensions
I would be grateful if you could help me

@mr katmar
Many thanks
I am starting to think that the phenomena may be due to following elements
- high gas velocity
- sudden contraction
- possible cavitation ?

I am wondering: is there a number that I can correlate to a cavitation phenomena ?

Thanks !

 

[zdas04]

Gas flow cannot cavitate. 45 m/s is above the velocity limits that many companies set, but those limits are pretty arbitrary (one client of mine usese 35 m/s as the design max, but no one fusses about exceeding it in actual operations), generally trying to reduce friction losses rather than the velocity limits we put on liquid flow to minimize erosion.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. ùGalileo Galilei, Italian Physicist

 

[PaulLag]

Many thanks mr zdas04

PLease, may I ask you if you have any experience concerning this whistiling phenomena ?
Have you ever faced to something similar ?

Many Thanks

 

[hacksaw]

PaulLag

Try uploading your sketch again, no cigar this time.

The issue is common where branch connectons are encountered.

 

[PaulLag]

Hello Mr. hacksaw

hope it works now

thanks in advance

 

[MortenA]

gas just makes noise when passing - especially in valves and other line items. Oh the number of puns there could be made here

Best regards, Morten

 

[hacksaw]

Interesting to see the velocity increase in the small diameter piping. First you need to carry out your flow analysis and identify the various pressure drops in your system.

Once you've done that, there are noise estimating procedures available in the technical literature.

Good luck,

 

[chicopee]

Just as an experiment, have you tried to reduce the gas velocity to determine if the whistle disappear?

 

[LittleInch]

Have you looked at something like this

http://www.gmrc.org/documents/CompressorStationPipingNoiseinterimreportfinal.pdf

given that 45m/sec would be colloquially referred to as "whistling along", it is not surprising that you've got issues. If the contraction is a sharp edge like you show it will not be good. You could try a much smoother or longer reducer to reduce the turbulence that must be occurring.

Any good reason why it is going at this velocity?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[georgeverghese]

There are at least 2 supermajor oil companies that have guidelines for estimating velocity induced noise in pipes ( typically used for checking for AIV issues during emergency flaring ). So you can check your company engineering books for these. If there arent any inhouse methods, and if this noise really bothers the plant operators, you can ask a noise consultant to crunch the numbers on their program and it will tell you what the noise level is in dbA at any specified location. Some programs will even tell you what frequency the noise is at. Piping noise is attenuated by increasing wall thickness or adding acoustic insulation. In the case of the latter solution, beware of chloride CUI if this is in a coastal location. At mach 0.13, guess you wont have any AIV issues, just plain noise.