Noise due to in line orifices 1

[eeratm]

Could anyone explain or give me equations that would help me find out noise levels in a single holed orifice plate. I am curious to know how adjusting the size of the orifice hole will affect noise levels. Thanks.

 

[poetix99]

The noise associated with fluid flow through or around an obstruction is predominantly due to "vortex shedding". For general background on this phenomenon, consult an undergraduate level fluid mechanics text.

Vortex shedding through an orifice will be less regular than vortex shedding around an obstruction such as a flagpole, but the idea is the same.

You could probably find some empirical data for orifice noise since orifice are so important in fluid metering applications, and the pressure fluctuations causing the fluid noise would also affect such applications.

There will, in fact, be many frequencies associated with such noise. Especially for higher and higher fluid velocities (or Reynolds Number), the noise might be nearly "white"; that is to say random in nature.

However, for certain conditions, the shedding frequency is directly proportional to the mean fluid velocity (no particular surprise):
Strouhal Number = constant = ~0.2 = (freq)*(dia)/vel.

 

[bvi]

Sound power level is driven primarily by flow rate and pressure drop. The energy disspated in the pressure drop results in pressure waves which are sound. The equation for sound power level in the pipe, downstream of the orifice, can be found in the following reference.

Designing Piping Systems Against Acoustically Induced Structural Fatigue”. Journal of Pressure Vessel Technology, Vol. 119, August 1997, F. L. Eisinger

 

[quark]

The link below deals with the noise because of control valves, and I think it is much similar to your application.

http://www.iceweb.com.au/Technical/ValveNoise.htm

Here is a good technical paper from Emerson Process Controls

http://www.fisherregulators.com/tec...amentals_of_Aerodynamic_Noise_d350491x012.pdf

They also have a free software to estimate the aerodynamic noise at

http://www.emersonprocess.com/Fisher/products/softwaredown/noisepredic.html

Regards,


Believe it or not : Eratosthenes, a 3rd century BC true philologist, calculated circumference of earth with the help of a stick and it's shadow. The error was just 4% to the present day calcuated value.

 

[vanstoja]

A good discussion of aerodynamic screech noise from an orifice can be found in:
Succi,G.P., "Flow-Generated Noise in Circular Cavities or How Teapots Whistle, Noise Control Engineering Journal, Jan.-Feb. 1986, pp.8-16.
Succi says in essence that the screech phenomenon is characterized by high amplitude narrowband peaks typically 50dB above the broadband noise level caused when acoustic pressure reacts back on the fluid flow to produce a coupled, feedback oscillation. For orifice screech, the length to diameter ratio must be between 0.5 and 2.0 where whistling occurred over a range of Reynold's Numbers from 55,000 to 240,000. It is essential that the inlet to the orifice be sharp-edged for the best production of screech tones. Pipe axial acoustic modes serve as the triggering frequencies for screech tones starting at airflow Mach numbers ranging from about 0.2 to 0.8 in Succi's tests of orifice L/D ratios of 0.5, 1.0 and 2.0