Reply To: Jos Koopman Conundrum

[Martin Johnson]

Hi Chris,
I begin to see your point, the nozzle may well flip sonic to sub-sonic and it would produce some “interesting” effects. Like you, I am eager to see just how much of an issue it is from the S160 tests.

With regard to designing with DeLaval nozzles, I tend to come at the problem from a designer’s point of view (since that is what I was). Ipso, if you can avoid supersonic flow, then do so as it eliminates the issues noted above. I also note that many locomotives have minimal storage volume in the exhaust system, so there is no storage to even out the flow reaching the blast nozzle. I realise there is not much room at the front end of a loco to put such storage. However, I have been making an effort over the last few years to look at steam engine design from fundamentals and if theory dictates that there ought to be storage, then space would need to be designed in. That is also how I come to be picking holes in what others have said before – as the song goes “It ain’t necessarily so”

Martin