Understanding SAE J1723 supercharger testing - transitions?

[Machina]

Hi all,
Where I'm currently working is refitting their supercharger facility and want to apply SAE J1723. Sounds like a simple request to apply the right standard but we're having some discussions about interpreting it. In particular the definition of the transitions.
The standard defines the length of the inlet pipe in terms of the diameter of that pipe, and specifically says 6 diameters in length ("A straight pipe, 6 diameters in length, ... prior to the entrance transition..."). Then it says the transition to the supercharger entry must not be more than 1.5 diameters but doesn't specifically say in length ("The entrance transition shall not exceed 1.5 diameters.").
The current discussion / argument is about what that means. Does it mean 1.5 diameters in length of transition from inlet pipe to supercharger entry? Or perhaps 1.5 diameters step? But if it's a step how can be 1.5 diameters? Or should the supercharger entry diameter not be more than 1.5 diameters?
There are similar statements for the exit transition.
If anyone could explain where and how the 1.5 diameters are to be measured it would be appreciated, or point me toward where I might find an answer.
Perhaps we're just making it more complicated than it needs to be; a couple of us read it one way but then our boss disagreed so we're stumped.
Thanks for your help,

 

[dgallup]

The 1.5 diameters is the length of the transition from the end of the straight tube to the inlet of the supercharger. Since it also says that the inlet system should be designed to provide the least amount of restriction possible, the transition obviously will NOT be a step. That would be one of the highest restrictions possible. I'm not really sure what is the best shape of the transition, probably a bellmouth but maybe just a simple cone.

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[Machina]

Thanks dgallup, that agrees with what my colleague and I were thinking. However our boss is the one who thinks otherwise so we'll have to convince him. Without meaning to be rude is there any way we can back up the argument? Any diagrams from SAE, explanations in reference books, or similar?

I only mentioned a step because I was trying to understand what other options there could be. Our boss is of the opininon that the diameter might refer to the supercharger intake (which I've pointed out could be, and often is, non-circular).

He thinks that the transition needs to be longer, to give the least restriction. Myself, I say that there's a standard and we should stick to it but when that standard is 100% clear then there are arguments.

Some of the problem migh come from the definition of the inlet pipe diameter which I think is maximum outside diameter of pipe, wouthout defining the inside diameter. And if it's a maximum limit it could be smaller. I don't have the standard in front of me at the moment so I'd have to check.

Anyway, thanks again for your help,

 

[Lou Scannon]

With transitions, the ideal shape for minimum restriction is an S curve. Laminar flow element installations provide a good example:

The higher the aspect ratio L/D, the lower the restriction, but a point of diminishing returns is reached and the LFE example is probably a reasonable compromise.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz