Lady Anne variation.

[milisavljevic]

Good morning, Graham!

What?! No comment on my haiku?! And here I thought that you would get a "kick" out of it.

While most of Vancouver is either asleep, drunk or stoned (or some combination of these)
I will put together a post with the results of my FWE-VIII analysis (aka "Alien Autopsy" ).

Although I admit to nursing a somewhat distracting caffeine "buzz"...must find more java!

Cheers!
M.

PS: And I will be taking a break to read my favourite newspaper, The Grauniad!

[Graham C. Williams]

Dear M.
Many Thanks.
I look forward to reading it. All Night, Oh Dear!
The poetry? It made me smile! Will you be publishing the collected works soon?

Best Regards
Graham.

[Graham C. Williams]

Dear M & M.
I used to think the use of a straight bit of pipe connecting combustor to tailpipe, (a timing devise; optimised for one half of the cycle only,) was an act of laziness on behalf of designers.
No, not now. Now I consider it to be only one of (at least) 2 paths. I've chosen to explore the other one. With a lot of help from those on this forum it's proven to be an interesting walk.

Graham.

[milisavljevic]

.
Hello Graham --

I look forward to reading it. All Night, Oh Dear!

Oh! I'm up all night, every night. Constructing a post for you is sandwiched in, hopefully done before I am.

The poetry? It made me smile! Will you be publishing the collected works soon?

Now there's an idea!

Cheers!
M.

[Graham C. Williams]

Dear Mike.
Here are the numbers you wanted.
The numbers represent the Velocity zero crossing points as a percentage of the unpacked motor.
The Tolerance in the first set is given by my acceptable upper and lower combustion gas velocity limits.
Where I have multiple crossing points I've shown these as second and third values.
The values are sampled at approximately equal time steps. The first value is taken just as cold air enters the CC. The second is when early combustion starts.
The last value is at peak pressure across the motor.
These samples were taken from a NUDiS thrust run at 4.9Lbsf.

I hope it helps
Regards
Graham.

[milisavljevic]

.
Dear Graham,

I used to think the use of a straight bit of pipe connecting combustor to tailpipe...
was an act of laziness on behalf of designers.

I agree.

It may also be an expedient, given the realities of enthusiast-built pulsejets, eg., the need for ready-made bends.

Now I consider it to be only one of (at least) 2 paths. I've chosen to explore the other one.

And I do not wish to discourage your explorations! My observation is that most, but perhaps not all, pulsejets can
be successfully fitted out with nothing other than a continuously expanding tailpipe, eg., as in Snecma's Ecrevisse.

A second observation is that concerns over timing are perhaps a bit of the "tail wagging the dog". Certainly it has
never transpired that in any pulsejet that I either designed or helped another to modify, that wave timing made a
detectable difference in its operation. And by wave timing, I do not mean acoustics. I'm all about acoustic tuning!

That said, there IS a continuing need to explore more complex tailpipe profiles, such as found on FWE VIII, all of
my QD types and superchines. I profile tailpipes primarily to manage volume, which in turns drives the Helmholtz
mode and acoustic synchronisation that are essential to proper operation in well-designed resonating combustors.

Which reminds me that I need to finish writing a certain post...

Cheers,
M.

[milisavljevic]

Just found your latest post!

These samples were taken from a NUDiS thrust run at 4.9 Lbsf.

Graham, what is the correlation between "% of unpacked pipe" and percent of acoustic length?
Is the "unpacked pipe" with the induction tube relocated to the front? Or the other way 'round?

Cheers,
M.

[Graham C. Williams]

Just found your latest post!

These samples were taken from a NUDiS thrust run at 4.9 Lbsf.

Graham, what is the correlation between "% of unpacked pipe" and percent of acoustic length?
Is the "unpacked pipe" with the induction tube relocated to the front? Or the other way 'round?

Cheers,
M.

I noticed an Error in the list. It's correct now!
The numbers here only relate to the Physical Length.
Yes, The induction pipe is at the front on this model. To the left ( towards zero percent)
I'll post another set related to the Acoustic length but must do this later, sorry.

Graham.

[Graham C. Williams]

Dear M.
Thinking again about how I generated the values.
The values shown relate to a physical location (strictly cell number) on the unpacked motor. The acoustic length of the motor has been taken into account by the Navier-Stokes equation during the calculation of these points.
Does that make more sense?

Regards
Graham.

[milisavljevic]

The numbers here only relate to the Physical Length.

Yes, The induction pipe is at the front on this model.

No need to repost your information for my benefit. Anything I post will be relative to the motor, as built,
either as a percentage of acoustic length or its actual physical length. Although Mike has explained what
unpacking means to me (possibly more than once), I don't grok it and can't really relate to it. It's just me.

If you provide me with the physical length of the unpacked motor, then I can convert to the original duct.

Cheers,
M.

Thinking on it more myself, I suspect as I don't have to unpack this type of duct, I don't get a feel for it?

[milisavljevic]

Dear Graham,

Thinking again about how I generated the values.

As an example, consider when I mentioned that the effective length of the the combustion zone
for FWE-VIII was 17.4% of the acoustic length (ie., to 100.5 mm of the 559 mm physical length);
where does this map to on the unpacked representation of this motor? This would help me a lot!

My caffeine buzz has devolved into a major headache...

Cheers,
M.

[Graham C. Williams]

If you provide me with the physical length of the unpacked motor, then I can convert to the original duct.

Cheers,
M.

The unpacked model I've used has a physical length of 696mm

Cheers
Graham.

[Graham C. Williams]

(ie., to 100.5 mm of the 559 mm physical length);
where does this map to on the unpacked representation of this motor? This would help me a lot!
Cheers,
M.

Ok. From the Open End of the Tailpipe to the Maximum dia of the CC : all the dims are as per my drawing.
The rest of the unpacked length is induction pipe and transition.
The lengths of the induction pipe and transition (in the unpacking) do not directly relate to the physical motor but the unpacked model produces results in NUDiS that satisfy my requirements.
I'll have a look at Mikes unpacking it's probably similar. It may be better.

Graham.

[milisavljevic]

Last from me, for now...

Ok. From the Open End of the Tailpipe to the Maximum dia of the CC : all the dims are as per my drawing.

Thanks! I can use this information to go back and forth between the two versions, actual and unpacked.

Cheers!
M.

[Mike Everman]

Hi guys! Lots went on since late last night!
My unpacking yields 624mm physical length. Mine is not "seeing" the closed end cone at all, rather it's considering the wavefront reflection starting right at the max cc dia. I'm still on the fence about whether to use the average length of the cone or not use it at all. I think the latter is correct, since I'm calculating the average path through the combustor, and that average length would be averaged out anyway. Anything beyond this average path through the combustor becomes a "sump" (M.'s suggested term, and very apt), that merely broadens pulse going through.

I'll do another write up of how I unpack a folded motor. This one was interesting in that the effective intake length gets buried in the end cone, protruding into the CC, just about to the point of the max cc dia.

On a Chinese, the intake goes right on the end, but getting the right effective length of the intake is the trick. That is, knowing what portion of the intake "connector" (another M. term, I prefer transition) is considered part of the intake, and how much is part of the CC volume.