Noise due to flow through orifice
Noise due to flow through orifice
(OP)
We have been testing a piezoelectric transducer connected to a small steel waveguide in close proximity to a flow orifice (~ 1 mm). The flow through the orifice should be subsonic since the pressure ratio is only about 0.4 (24 psig inlet, 14.7 psig outlet). However, we have encountered a phonomenon where the acoustic noise level increases by over 10X when the Reynolds number in the orifice goes above 1000. From 16 to 24 psig the noise level is at 1, then abover 24 psig, the noise increases to 10 or higher. I could understand if there was critical flow that there would be small sonic shockwaves, but that should not occur until approx. 30 psig.
Does anyone know why this occurs? It is just turbulence? We have tested several orifice sizes. While the increase in noise occurs at a different differential pressure for each one, the Reynolds number in the orifice is the same (!1000) at the pressure ratio where the noise increases.
Thanks,
Lee
Does anyone know why this occurs? It is just turbulence? We have tested several orifice sizes. While the increase in noise occurs at a different differential pressure for each one, the Reynolds number in the orifice is the same (!1000) at the pressure ratio where the noise increases.
Thanks,
Lee





RE: Noise due to flow through orifice
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The discussion is very good.
Regards,
RE: Noise due to flow through orifice
Do you really mean 24 psig inlet and 14.7 psig outlet?
Can the 14.7 be psia?
If so, then you are going sonic. The 24 psig would be 38.7 psia to the 14.7 psia.
RE: Noise due to flow through orifice
RE: Noise due to flow through orifice
Partially correct?
Hmmm not bad considering the information given.
RE: Noise due to flow through orifice
RE: Noise due to flow through orifice
The peak frequency at any Re can be determined from the equation f=St*U/d where U is jet velocity and d is orifice diameter. If you get a noise spectrum you can check for jet shear layer instability peaks. Another jet noise source is the so-called "preferred" mode, a downstream columnar resonance present at all Reynolds Numbers with a Strouhal Number between 0.25 and 0.5 which yields lower frequencies than shear layer instability peaks.
RE: Noise due to flow through orifice
RE: Noise due to flow through orifice
athomas236