milisavljevic wrote:I am uncomfortable wrt. the business of folding and unfolding motors that are intended to built in the
now-classic
"FWE style". Depending upon their relative dimensions (not those found in the
TARDIS),
many such ducts will behave as closed-pipe resonators; however, unfolding them results in what will
typically behave as an open-pipe. The unfolding also creates other problems. It is an interesting idea.
Though this was in response to Graham, I'd like to comment on it, since I generally follow his lead on "how to do it" with UFLOW1D.
My own feeling is that it is impossible to "unfold" or "unpack" classic FWE type engines (or Chinese, or Thermojet, or concentric engines, or ...) in a way that makes a linear model that is truly
equivalent. A linear engine (I mean a real one, like Graham and Nick's Type 07) is
literally describable in one-dimensional terms (except for very minor effects at exit flares, which can be ignored for basic analysis), but any engine that excites the intake by reflecting wave energy back through the chamber (or any other part) is inherently multi-dimensional. You can figure out how to model them as APPROXIMATELY
acoustically equivalent or APPROXIMATELY
flow equivalent, but not both at the same time.
I don't believe the UFLOW1D model of a "folded" engine is EVER
realistic; I only hold that it is still
useful for design, if its inherent limitations (which are many and varied) are kept in mind. In general, the most important consideration is to get the resonances "locked in", and UFLOW1D will help you do that, at least approximately. There is probably no modelling technique that will achieve a perfect simulation, unless all the temperatures in the actual running engine could be measured to high accuracy (and if you could do that, why would you need to model it? ;-).
L Cottrill