FWE Theoretical Intake Flare Examples

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larry cottrill
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FWE Theoretical Intake Flare Examples

Post by larry cottrill » Fri Dec 02, 2005 9:00 pm

I took the time with UFLOW1D to investigate the theoretical effect of changes to the intake flare on the standard FWE design. Eric has claimed that the flare of the intake makes a significant difference to how well the engine runs - and the theoretical trials with UFLOW bear this out. Below are comparisons of no flare, 1.25 inch diameter flare, 1.5 inch diameter flare and a venturi design. Note that the vertical scales of these graphs varies from example to example!

The standard FWE has an internal intake diamer of about 23 mm, using 3/4 inch EMT (rigid steel conduit), and this is the basis for this comparison. The first graphic shows the theoretical values for one cycle and a square-cut, unflared intake. What you should look at in these comparisons is the white line in the Mach Number and Mass Flow graphs - this represents the speed and mass flow values for a point about 5 mm inside the intake flare. The blue line is the tail end of the engine, and is included just to show the timing between intake and tailpipe events. Remember that the instantaneous value of thrust is velocity TIMES mass flow, so an improvement in either one goes a long way.

The second example is exactly the same except that the outer 10mm of the intake has been expanded out to a flare of 32mm diameter (about 1.25 inch). Note that the initial blast wave now produces a brief flow at slightly greater than Mach 1 velocity! While this is a very brief part of the cycle, it is considerably better than the earlier value. Where the blue line comes up positive and the white line swings negative, the flows are inward - the engine is in aspiration. In these areas, the lines appear 'flatter' than in the earlier example, but this is just because of the change in vertical scale - the actual values are slightly better. It is also certainly true that UFLOW cannot take into account the multidimensional nature of the inflow near the rim of the flare, so the flare will actually accomplish more in the intake phase than this would make it appear.

The third example is the same except for expanding the flare to 38mm (about 1.5 inches). Again, the vertical scale changes, but there is a little more improvement in the white curves.

The last graphic is a simple venturi, which could be used (for example) in liquid fueling experiments. The inlet to the venturi acts as the flare, and surprisingly, even though the throat is smaller than the rest of the tube, performance is reasonable, with the velocity curve almost identical to the 32 mm flare and massflow about the same as the unflared tube. The ID dimensions of the venturi to achieve this performance was VERY critical - making the throat either a mm larger or smaller ruined performance, as did making the inlet rim or tube ID larger. The dimensions are:
ID of inlet rim: 23 mm
ID of throat: 19 mm
Intake tube ID: 23 mm
Distance of throat to inlet rim: 10 mm
Length of throat: 5 mm (this should be non-critical)
Distance of throat to full tube ID: 25 mm (this could be reduced, however - it should be non-critical)

L Cottrill
Attachments
FWE_venturi_intake_1.jpg
Intake venturi - 23 mm ID at each end, 19 mm ID in the throat. Graphic Copyright 2005 Larry Cottrill
FWE_venturi_intake_1.jpg (154.95 KiB) Viewed 9181 times
FWE_38mm_intake_flare_1.jpg
Perfomance with intake 38 mm (1.5 inch) edge diameter intake flare. Graphic Copyright 2005 Larry Cottrill
FWE_38mm_intake_flare_1.jpg (152.42 KiB) Viewed 9182 times
FWE_32mm_intake_flare_1.jpg
Engine curves with 32 mm (1.25 inch) rim diameter intake flare on 23 mm ID intake pipe. Graphic Copyright 2005 Larry Cottrill
FWE_32mm_intake_flare_1.jpg (153.27 KiB) Viewed 9181 times
FWE_no_intake_flare_1.jpg
Standard FWE performance curves with straight unflared intake. Intake ID is 23 mm (3/4-inch EMT intake tube). Graphic Copyright 2005 Larry Cottrill
FWE_no_intake_flare_1.jpg (153.23 KiB) Viewed 9181 times

hinote
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Re: FWE Theoretical Intake Flare Examples

Post by hinote » Sat Dec 03, 2005 1:27 am

Larry Cottrill wrote:I took the time with UFLOW1D to investigate the theoretical effect of changes to the intake flare on the standard FWE design. Eric has claimed that the flare of the intake makes a significant difference to how well the engine runs - and the theoretical trials with UFLOW bear this out.
Larry:

Thanks for bringing this subject up.

I know that Eric has recently been promoting a wide flare.

I can also tell you that Mike E. has been promoting just the opposite.

Currently, I have cut the front 1/3 (approx.) off the intake of my M8E engine; I have devised a sleeve, and will be able to test several intake front-end concepts, as well as attempting to fine-tune the intake length, ala the "SNECMA papers". BTW verification of optimized intake length with this engine will be reiterated into UFlow, to fine-tune its design capabilities in this critical area.

Please see the 2 attached images.

The first is a shot of the 2 intake schemes currently planned for the M8E.

The 2nd is a parallel project, that you-all will soon be hearing more about. I devised a method of producing a "fancier-looking" intake, which has a classic shape--after the so-called "Borda mouth".

Stay tuned--I'm currently retired and busier than a one-armed paper hanger, regarding my pulsejet activities.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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mini Borda mouth.JPG
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intake flare schemes.JPG
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hinote
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Re: FWE Theoretical Intake Flare Examples

Post by hinote » Sat Dec 03, 2005 1:40 am

Larry Cottrill wrote:I took the time with UFLOW1D to investigate the theoretical effect of changes to the intake flare on the standard FWE design.
Larry:

I don't want to shoot-down your efforts--BUT:

Several of us have observed misbehavior in the UFlow model, when attempting to use it to design valveless pulsejets. Specifically, UFlow has failed to model the effects of the intake flare, relative to the operation of the rest of the engine.

It appears to be one more anomaly that has to be considered when using UFlow. I'll be looking at your effort and trying to see how it should be considered in light of the overall efforts we're making to design pulsejets.

Thanks for your efforts!!

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Eric
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re: FWE Theoretical Intake Flare Examples

Post by Eric » Sat Dec 03, 2005 3:42 am

The intake is very important, as we all know :)

For the smaller engines I usually promote a big flare since it helps overcome some of the aerodynamic innefficiencies of small diameter tubes, and can also help ballance things out in big engines that arent quite perfected.

It cant just be any size though, it has to be just the right size.

I dont put much faith in uflow for the intake, since the flow has very little correlation with what is going on with the wave action in the intake.

Eric
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Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

larry cottrill
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re: FWE Theoretical Intake Flare Examples

Post by larry cottrill » Mon Dec 05, 2005 3:51 pm

I think this is one of the cases where UFLOW1D isn't really wrong - just inadequate. UFLOW sees changes in velocity, etc. only in the longitudinal direction (i.e. along the tube axis). This is inherent in a one-dimensional approach. He can't take into account things like lateral motion - the flare is seen as a simple nozzle in one flow direction and a simple diffuser in the other. So, the influence of "surrounding" free air is sort of "missing".

I was not trying to say this was a final answer for design, and obviously should have re-emphasized the program's shortcomings in this case. I just thought it was interesting that a one-dimensional model could, in fact, show a significant effect for end flares of varying dimensions. Especially intriguing is the sonic velocity of outward flow in the blast phase.

L Cottrill

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re: FWE Theoretical Intake Flare Examples

Post by Carl Litzkow » Wed Dec 07, 2005 3:54 pm

Larry,
Having abused and exploded many a flathead Ford and small block Chevy engine, I know the importance of tuning intake/exhaust.

Every time I have a new idea to contribute, I find the wheel has already been invented. I had already gathered parts for a removable " intake manifold" so one could bolt/unbolt a new intake tube config for evaluation. I was also going to allow for +/- ( fore/aft ) mounting of tube to evaluate that position as well. My Question is should I use your 7" set back as a ref to vary +/- from ?

Your FWE ver V is alive and well. Been "jpeging" as I go. The only thing I lack is to roll the exhaust tube and get use of left arm back.

larry cottrill
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Re: re: FWE Theoretical Intake Flare Examples

Post by larry cottrill » Wed Dec 07, 2005 4:06 pm

Carl Litzkow wrote:Every time I have a new idea to contribute, I find the wheel has already been invented. I had already gathered parts for a removable " intake manifold" so one could bolt/unbolt a new intake tube config for evaluation. I was also going to allow for +/- ( fore/aft ) mounting of tube to evaluate that position as well. My Question is should I use your 7" set back as a ref to vary +/- from ?
Yes, I would work from that. And, I think you can take an even simpler approach - hold that 7 inches constant and just play with the position of the flare itself, starting at what I show on the drawing. I'm now pretty much convinced that the position of the END of the intake is far more critical than the point at which it enters the chamber (until Mike or somebody like you proves this is just wrong) - so, start out by going at it that way. Remember also that the engine will be at least three times as sensitive to variations in the intake position as it will be to the tailpipe length! Make changes very gradually during testing.

Oh, and ... even if it happens to kick off and run the first time (ha!), you should still do some messing with slight changes in the intake position and record what happens. We might all learn something from that!
Your FWE ver V is alive and well. Been "jpeging" as I go. The only thing I lack is to roll the exhaust tube and get use of left arm back.
Carl, that sounds great. Hope the arm starts working well soon, though I know this will probably be a gradual process. On the engine, just take it at your own pace. If you have any construction photos to post, go back to the original thread (or start a new thread for construction, if you have a lot that you think is worth showing).

L Cottrill

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re: FWE Theoretical Intake Flare Examples

Post by Carl Litzkow » Wed Dec 07, 2005 4:25 pm

Hello Bill H.
This is the first time I've had a chance to hyber-talk with you since I joined. I tried to read as much as my decaying gray matter could absorb before I posted. Just want to be helpfull.
I know you are serious about your PJ's and I have had 2 ideas for making flares.
The first was to combine metal spinning with an Oxy Acet to "encourage" the formation ( or deformation) as posted above to Larry.
The second would be done cold using a lathe turned metal male/female mandrel set under the "influence" of my 12 ton press. I felt the metal mandrels would suck away the heat as soon as they came in contact, so probably won't bother preheating.
Since turnig the mandrel is so labor intensive, could you please give me your best guesstimate as to shape and rate of flare. If all goes well dia. won't be to important since the taper should accomadate various diameters.
Don't know if these are good ideas,just ideas. Time will tell.

Carl Litzkow
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re: FWE Theoretical Intake Flare Examples

Post by Carl Litzkow » Wed Dec 07, 2005 4:51 pm

Larry,
Will do - yes, not acomadating for +/- placement does simply. I didn't mention that like Bill H. I can adjust tube length and do a "quick change" of flare config using a 1 1/2" EMT coupler. It has 4 set screws and when the pipes are pushed in all the way makes a pretty good "aerodynamic" connection. One problem might be it is an Aluminum casting and won't take a lot of heat. If it melts, good cut and weld to rescue
I feel naked without spell check, hopefully you will get the meaning. I appreciate your sugestion of mailing it to myself so I can use spell check, but that time could be better spent welding - right ?

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Re: re: FWE Theoretical Intake Flare Examples

Post by hinote » Wed Dec 07, 2005 5:38 pm

Carl Litzkow wrote: Since turnig the mandrel is so labor intensive, could you please give me your best guesstimate as to shape and rate of flare. If all goes well dia. won't be to important since the taper should accomadate various diameters.
Don't know if these are good ideas,just ideas. Time will tell.
I can only offer you the observations I have made, on my successfully operating engines.

The most consistent results have been with a simple sheet-metal cone, welded to the front of the intake tube. I'm using an L/D ratio of not less than one, and not more than about 1.4. Angle is 16 degrees each side, 32 degrees included. Be sure to blend the joint on the inside (I use a die grinder) for smoother airflow.

The other successful concept was the trumpet, formed by an exhaust shop (see my post "Bill's Tip o' the Day", in the Tools and Construction section). This has been successful on my smaller intake tubes.

Method-wise, it's a matter of "whatever gets the job done", IMO.

Also, attached is a more sophisticated approach to the intake flare, from previous posts. The classic Borda Mouth is more complex than anyone is currently using; whether it creates additional flow is still TBD.

Bill H.
Acoustic Propoulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."
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Re: re: FWE Theoretical Intake Flare Examples

Post by hinote » Wed Dec 07, 2005 5:52 pm

Carl Litzkow wrote: could you please give me your best guesstimate as to shape and rate of flare. If all goes well dia. won't be to important since the taper should accomadate various diameters.
Rate of flare and max flare angle are still unknowns. Everything seems to work for better or worse--so I wouldn't be afraid to try some different dimensions. As stated above this would be a good research project for somebody like you.

An easy way to adjust intake length, and to try different intake flares-- is to use a "wrap" of thin aluminum flashing from the hardware store. I use 2 hose clamps on each side of the joint. The aluminum will last long enough for experiments--the intake stays pretty cold (depends on the engine).

Also look at this old thread, for Dave's excellent forming method, and a good discussion on the "Borda mouth":

http://www.pulse-jets.com/phpbb2/viewtopic.php?t=1460

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Carl Litzkow
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re: FWE Theoretical Intake Flare Examples

Post by Carl Litzkow » Wed Dec 07, 2005 6:14 pm

Thank You Bill,
The only thing wrong with the trailer hitch idea is I wish I had thought of it first.
And thank you Dave, what a great idea, I knew I saved those old hitch balls for some reason.

hinote
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Re: re: FWE Theoretical Intake Flare Examples

Post by hinote » Wed Dec 07, 2005 9:28 pm

Carl Litzkow wrote: The second would be done cold using a lathe turned metal male/female mandrel set under the "influence" of my 12 ton press. I felt the metal mandrels would suck away the heat as soon as they came in contact, so probably won't bother preheating.
Just an opinion here:

You may find that POST-heating is necessary, to relieve the metal between flaring attempts. I would suggest moving in multiple, smaller increments.

I've already had the experience of tubing splits, while attempting to hand-form a flare--so some sort of relief would seem appropros.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

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