What is the relationship between Mach Number and Air Flow Noise?

[8911101]

What is the relationship between Mach Number and Air Flow Noise? What is the threshold of Mach that air flow noise is audible?

 

[GregLocock]

In what sort of system?

Typically in an exhaust manifold/downpipe you'll start to hear Mach noise at around 0.6-0.8 M bulk flow rate, as there is enough local acceleration to get you into trouble.

In an HVAC system you can hear flow noise at much slower speeds than that, .05M or less.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[8911101]

Thanks, Greg. I am talking about air intake system, and turbocharger intake noise. Would you expand a little more why different systems have various Mach noise? Frequency dependent?

 

[GregLocock]

What do YOU mean by Mach noise?

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[8911101]

Oops.. I mean Flow noise, not Mach noise.

 

[GregLocock]

Well to be honest that is far too big a subject to cover in a post. or even a book. Basically it comes down to how the noise is generated, and then how much is filtered out or amplified before anyone hears it.




Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[SomptingGuy]

So you are talking about noise created by turbulence around the compressor blades then, not regular "flow noise" (e.g. that you would get from an exhaust). This is not really connected to flow rate, more likely where on the compressor map you are operating. If you are near or over the stall line, expect whoosh noise.


- Steve

 

[GregLocock]

In that particular case, any turbulence upstream of the blades is amplified by the pressure change process, in a non linear fashion. So in general if noise is your concern, spend more time refining the intake duct than the exhaust duct around a bladed impeller.

Cheers

Greg Locock

I rarely exceed 1.79 x 10^12 furlongs per fortnight

 

[crjones]

Generally i have found the air flow velocity of 750 feet/min there will be audible noise.

 

[spongebob007]

At my past job I did some work similar to what I think you might be looking for. I used this book extensively for that project:

http://www.amazon.com/Noise-Vibrati...=sr_1_1?ie=UTF8&s=books&qid=1263592832&sr=1-1