Exactly ... That's what I trying to illustrate ...Mike Everman wrote:I think I can help illustrate what luc is talking about in a general sense with the attached illustration of basic methods.
What got me deep into pulse-jets in the first place was the seeming impossibility of removing the noise from the pulsejet. Any way you care to look at it, you can't separate "sound" from pressure oscillations. they are synonymous, and the one you need to be so energetic is the fundamental. In most of my small motors, it's at 200 Hz plus.
Since working on single engine approaches, I had diverted to cluster engines, so spent all my time on smaller motors. The not-so-original thought being driving the frequency up, and virtually driving that frequency up by them adopting random phasing. Enforcing a specific (semi cancelling, like in pairs or 3-phase) phasing hasn't been easily achievable with a DIY'er skill set.
And although in agreement with you about the pressure and noise close relation, I never tried to dissociate either one, but just using and "Flowing" sound so it comes and kill that sound (And pressure) once I was done with it (i.e. : Got the thrust or heat or velocity I wanted).
Always keep in mind that as gas turbine and also a majority of jet engine, gases exit the tail pipe at near ambient pressure. So once pressure is gone, you can do all you want with "Noise".
Watch my next posting and image ... I think this will raise few memories ...