Restriction Orifice Noise

[valvepuke]

I am looking for a method for calculating AERODYNAMIC noise generated in a pipe due to a restriction orifice. I am familiar with the IEC method for aerodynamic noise prediction in control valves and think some of the same principles might apply to an orifice. If one uses the same approach, there needs to be first a determination of the sound pressure level generated inside the pipe by the gas flowing through the orifice. The next thing is to determine the transmission loss through the pipe and then an adjustment for the equivalent sound pressure level at 1 meter out from the pipe wall. Like the control valve aerodynamic noise calcs, I would think that consideration should be given to the Mach No. of both the gas exiting the orifice and the gas in the downstream pipe.

We are challenged often on this by our clients, especially when the pressure drops across the restriction orifice indicates that critical flow exists.

If anyone has encountered the need for predicting RO noise and has experience in this I would appreciate some advice.

 

[stanier]

Why not use your control valve sizing software and imitate the orifice with say a ball valve? Close the valve to 60 degrees or so with a comparable orifice sizing to the orifice plate.

 

[valvepuke]

Thanks, Stanier. I am currently taking a similar approach to what you suggested. The IEC 60534-8-3 gives an equation for the noise produced by an outlet expander fitted to the outlet of a valve. This equation includes the effects of the flow from the smaller inside diameter of the expander up to the in downstream piping ID. This would be sort of like an orifice. The noise generated by the expander is separate from the noise of the valve, which has its own set of noise equations. To the noise generated by the expander-induced gas turbulence we add the transmission loss through the pipe wall and a Mach number correction and the result is the total expander sound pressure level at 1 meter from the pipe. I think this approach might be something that my client can live with as I have not found any "canned" equations that specifically address restriction orifice noise. I hope to hear from other sources on this. Again, thanks for your reply.