Noise enclosure for supersonic nozzle
Noise enclosure for supersonic nozzle
(OP)
Hi all,
we have to build an enclosure to attenuate an SPL of 137 dBA @ 6 ft, coming from a high-temp supersonic nozzle.
A double-walled enclosure with all due precautions and acoustic tricks should provide the 55 dBA attenuation, but we need to reach 60 dBA attenuation and I'm especially worried about noise induced vibrations from the very-low-frequency components of this noise (i.e. everything below 100 Hz).
I think we need to rest the inner shell of the enclosure on low freq. spring suspension. The issue is estimating the vibration level that will be induced on the enclosure walls, floor and ceiling, but we only have octave-band levels between 63 to 4K, nothing on the very low freq. range. Noise Spectrum data provided by nozzle manuf. follows:
Freq. SPL dB
63 91
125 100
250 101
500 112
1000 118
2000 123
4000 126
ALL LEVELS UNWEIGHTED
The nozzle ejects 9 kg/min of exhaust gases (CO2, H2O, N2) @ 1500ºC
Anyone knows what is the noise spectrum shape for this kind of exhausts?
Thanks and regards!
EB
we have to build an enclosure to attenuate an SPL of 137 dBA @ 6 ft, coming from a high-temp supersonic nozzle.
A double-walled enclosure with all due precautions and acoustic tricks should provide the 55 dBA attenuation, but we need to reach 60 dBA attenuation and I'm especially worried about noise induced vibrations from the very-low-frequency components of this noise (i.e. everything below 100 Hz).
I think we need to rest the inner shell of the enclosure on low freq. spring suspension. The issue is estimating the vibration level that will be induced on the enclosure walls, floor and ceiling, but we only have octave-band levels between 63 to 4K, nothing on the very low freq. range. Noise Spectrum data provided by nozzle manuf. follows:
Freq. SPL dB
63 91
125 100
250 101
500 112
1000 118
2000 123
4000 126
ALL LEVELS UNWEIGHTED
The nozzle ejects 9 kg/min of exhaust gases (CO2, H2O, N2) @ 1500ºC
Anyone knows what is the noise spectrum shape for this kind of exhausts?
Thanks and regards!
EB





RE: Noise enclosure for supersonic nozzle
I'm surprised the manufacturer can't give you a more complete/finer resolution spectrum. Ask them for the actual data (either time records, or psd's) from the test(s) that was/were used to generate the octave-band data.
Do you know the fuel/oxidizer combination? This can help indicate whether to expect low-frequency "pops and bangs"...hydrocarbon fuels tend to do that more than the hydrazines.
RE: Noise enclosure for supersonic nozzle
The manufacturer won't give more info because they want to sell their (very expensive) enclosure...
The fuel is propane and oxidizer is air.
RE: Noise enclosure for supersonic nozzle
RE: Noise enclosure for supersonic nozzle
That is one remarkable attenuation for a single wall... if it was purely mass-driven, it would take something like 180 kg/m2 to get to that attenuation. If it's a composite wall (which it has to be), then probably 40 kg/m2, but it need to have something incredibly heavy and very clever elastic provisions inside.
Any thoughts? The costs of the double walled-floating booth are too high for what the customer can pay...