UFLOW trainer VPJ

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serverlan
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UFLOW trainer VPJ

Post by serverlan » Tue Sep 20, 2005 1:26 pm

Hi guys,

here is a basic version of the sort of jet I have been playing with in UFLOW. (attached)

Its purpose is to give a clear example of the basic concepts of valveless pulsejet operation, rather than to focus on any amazing performance etc.
Sort of a Trainer.

I don't have any significant points set.
I just run the simulation and then look at it change with time in the "graphics" display screen.

The simulation time is set to about one cycle. (If should run a bit over 300 Hz)
It starts with a combustion pulse, which moves both ways.
The input restriction is designed to minimuse reflections, so that we get neither positive nor negative pulses introduced into the simulation.
This is mainly for clarity, so I can see what is going on.
There is a bit of oscillation, but not too much.Of course, there is a fair amound of thrust lost through the intake. This could be compensated for by bending it into a U shape.

Meanwhile, the pressure pulse moves down the exhaust, producing a significant mass flow at the exhaust for part of the cycle. By this time the pulse has spread a bit.
Looking carefully, you can see a negative (below atmospheric) "Kadency" wave travel back up to the inlet. During this time, you can also see a reasonable amount of positive mass flow at the inlet, representing fresh air being drawn in.

One the negative wave reaches the front again, it is mostly nullified by the non-reflecting nature of the intake, and the system is stable once more.
Hopefully by now it has a fresh fuel/air charge and is ready to repeat the process.

A flared exhaust improves the mass flow (thrust). Presumably it also weakens the negative pulse, but this effect seems negligible.

I have tried flared combustion chambers like the Lockwood, but they introduce so many secondary waves and reflections that I can't tell what is happening any more.

Perhaps someone out this with a runniong lockwood would do a small experiment for me? Simply block about half the area of the intake, perhaps with a washer or similar. This would make it like my design, but with a combustion chamber. If you could let me know if this makes it harder to start or easier, more or less thrust, perhaps more or less efficient?

Well,
thats about the best I can do. Time to build one (or wait till someone else does so)

Happy simulating.

Don
Attachments
best.IMM.txt
UFLOW VPJ trainer - remove the .txt extension
(247 Bytes) Downloaded 530 times

serverlan
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re: UFLOW trainer VPJ

Post by serverlan » Thu Nov 10, 2005 2:27 am

Larry,

I think this may be relevant to what you are noticing in UFLOW

Don

thecheat
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re: UFLOW trainer VPJ

Post by thecheat » Thu Nov 10, 2005 3:04 am

does this work? when I downloaded it, it was just a mass of odd symbols and I couldn't seem to remove the txt. help?
Lasers, jets, and helicopters HURAH!

serverlan
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re: UFLOW trainer VPJ

Post by serverlan » Thu Nov 10, 2005 3:27 am

err. sorry.

If you are using Microsoft Internet Explorer,
Right clik on the link, and do a Save As...

In the dialog, set the file type to "all files"
and remove the .txt extension.

don

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re: UFLOW trainer VPJ

Post by Jim Berquist » Thu Nov 10, 2005 3:29 am

I checked it out too and only received garble...IMM what is that??
WHAT TO FRAP, IT WORKED![url=callto://james.a.berquist]Image[/url]

serverlan
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re: UFLOW trainer VPJ

Post by serverlan » Thu Nov 10, 2005 3:44 am

Its the file thformat that UFLOW1D reads/writes.

If you can get it downloaded as Best[1].IMM
Then start up Uflow1d.exe
Use file - Open to open Best[1].IMM.
Then, click on the Contour tab to see the minimalist engine design.
(Combustion is designed to occur about 1/5 the way along, in section 3)

Use menu Calculate - Play to get it to run the simulation.

Click on the Graphics Output tab to see the simulation at time t=0
You will see four charts - pressure, density, mach number, and mass flow

Use the scroll bar on the right to scroll it forwards through time.

It starts with a pressure pulse due to the combustion. Density is high to the left (cooler intake area) and low to the right (hot combustion/exhaust area.

Don

serverlan
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re: UFLOW trainer VPJ

Post by serverlan » Thu Nov 10, 2005 4:04 am

Actually, I think the simulation is better if you reduce the length of segment 2 to 0.01 m.

This puts the combustion very near the intake,
which corressponds to where fuel/air mix is sucked in,
and would combust,
and so would be more consistent with the next cycle.

Its a bit harder to understand though, as the left and right pulses are not as clearly separated.

Don

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re: UFLOW trainer VPJ

Post by leo » Thu Nov 10, 2005 8:49 am

the program link for downloading UFLOW is in this topic.
http://www.pulse-jets.com/phpbb2/viewtopic.php?t=2406

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re: UFLOW trainer VPJ

Post by Eric » Thu Nov 10, 2005 9:46 am

Leo I have been meaning to tell you that pulsejet gif is great! Did you make it?

Eric
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re: UFLOW trainer VPJ

Post by Jonny69 » Thu Nov 10, 2005 1:59 pm

Also Leo I pointed someone to the gif in your signature because they couldn't work out how the FWE I made was going to work. Pictures speaking a thousand words type thing, hope you don't mind. It's a fantastic animation!

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re: UFLOW trainer VPJ

Post by leo » Thu Nov 10, 2005 11:55 pm

Thank for the compliment on my animated Gif everybody.
I made it to explain to people how this things work.
It isn’t accurate bud so what, nobody knows how these things exactly work.
I made it in Paint Shop Pro 7, with the use of layers.
The contour I used is from the measurements of Ed Knesl his EDK-02A where I made a cad drawing off.

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re: UFLOW trainer VPJ

Post by Eric » Fri Nov 11, 2005 2:10 am

Leo,
Its actually a lot more accurate than you give yourself credit for. Very good job. I might make a few for my about pulsejet page.
I was making an animated video using 3dstudio, but that is going to be a while. Now I just need someone with a really good voice to narrate it .... maybe Morgan Freeman, he seems to do a lot of documentary type stuff :P

Eric
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