Bruno Ogorelec wrote:Larry, why can't you turn around the process next and pretend that the tailpipe was of minuscule size and analyze the events in the intake, in the same way you did with the tailpipe in the first step.
Maybe you would arrive at two sets of results that might usefully fit together.
I'm sure you can do that. I'm sure you cannot do it perfectly. One problem I have with analysis of the intake, though, is deciding what gas and pipe temperatures to use. Both must be fairly low compared to the tailpipe, in the case of my engines, anyway. Another problem is that my intakes always come in at odd angles - that's a lot harder to simulate than an inline pipe, since UFLOW1D
assumes symmetry around an axis. In the classic FWE, how far is it from the inner end of the pipe to the "bottom" of the chamber? What does that pipe see as the "bottom" of the chamber? We would have to assume the front dome, I guess, and calculate the position of the pipe according to wave path length. What else could we do? Doing this, we would need a "rear plate" on the chamber at the inner end of the pipe, which means the chamber modeled would be much shorter than reality - would this be OK? I'm not sure ... there would be a lot more internal reflection than in the real chamber, but maybe that could be easily sorted out.
Yes, I need to look at this more closely and see how some variations work. I certainly have enough real-life examples now from running engines, as far as the dimensions are concerned. The Smooth Lady seems like a simple case to model - practically a straight-in Thermojet clone, as far as the intake is concerned.
When I have tried crude analysis of the intake before, it was always by artificially swinging it around to the front (using the 'Reynst Point' as a fulcrum), making a 'linear' engine with a somewhat shortened chamber. While this seemed
to show reasonable results with carefully tweaked temperatures, it is not an ideal solution, because it changes the operation of the pipe as a whole. It has been suggested that lengthening
the chamber by swinging the intake around the front plate (pressure antinode) would be the right way, since this makes sense acoustically - however, that alters the total gas mass considerably.
It's at least possible that there simply is no highly accurate way to model such designs with 1-dimensional analysis methods. But of course, it's also possible that some method (or combination) will be good enough