Ogge wrote:All I was pointing out is that geometry will change pulse shapes of the reflections. Yes, standing waves exist, but they are not perfect standing waves. If they were, you would get basicly a single tone out of a pulsejet. That is obviously not the case. Yes there are dominant frequencies and they are the ones you are using to establish your standing waves with.
As a matter of fact you will be getting at least 3 standing waves if not more. You will get a standing wave in the exhaust tube as well as in the intake tube and the interaction of their sum. These standing waves are generated by the interaction of waves propogating down the tube vs the reflections from the other end. To get a standing wave you MUST have waves traveling in opposite directions that sum to generate the standing wave.
Surely you're also getting other harmonics of the basic standing waves. Therefore, shouldn't it be an aim shifting the harmonics for forming a kind of "minimal multiple" as sum?
By trying to apply or rather applying a special temperature distribution and/or
(depends on each other and the above) a special wavelength distribution?
Or even forming a special frequency distribution, depending on the energy/heat release amount and thereof the temperatures that are then (re-)affecting the cycle?
If I understood it right, forming a "lock-up" that Milisavljevic mentioned some day?
But he never really clarified what he ment by "lock-up". Bill Hinote, could you eventually help here?
Eric wrote:You are not going to find any simple way to describe what is going on in a pulsejet, by anymeans. Wether using CFD, pressure sensors, or anything else.
You have an engine at one second full of 2500 degree ++ gases expanding, flowing out of the engine and continuing to burn and expand along the way, have various restrictions from pipe design, imparting heat to the tailpipe depending on local tailpipe heat pressure velocity etc, and at this point your speed of sound will be very high, so naturally any frequency will differ at any point in the engine at any time.
Then during the intake stage you have (in my case) below 0 air temp flowing over a thin boundry layer clinging to the metal. This cold air is ever changing in volume, as is differential between the two layers, and their wildly varying temperatures, and pockets of mixing gas, will throw off the speed of sound average drastically, and if you look at the individual sections not as an average things are even more different.
When the speed of sound changes, the frequency will change, and since there will be no single speed of sound in the engine at any point in time you will get grotesque looking wave patterns, all in rapidly changing proportions and frequencies.
We all should internalize these facts.
But surely most of the "insiders" (I mean people being more or less deeper in the pulsejet theoretics) here should already know it.
We rather should want to work with
these facts, not against
Sooooo complicated. But simplified models are