dynamic modeling of a strip valve

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WebPilot
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Re: dynamic modeling of a strip valve

Post by WebPilot » Sat Oct 18, 2008 10:31 pm

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Re: dynamic modeling of a strip valve

Post by WebPilot » Mon Oct 20, 2008 4:56 pm

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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Oct 23, 2008 2:02 am

adding a few lines to the just previous ...

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Re: dynamic modeling of a strip valve

Post by WebPilot » Fri Oct 24, 2008 5:17 am

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Re: dynamic modeling of a strip valve

Post by BinaryReaper » Wed Oct 29, 2008 5:55 am

webpilot I just wanted to say That I think i may be "that guy" you got the concept from. Its been a handle of mine for years, and I am quite active on the internet in a number of ways. I goggled "BinaryReaper" just out of curiosity and found this page, and felt I had to say something. I agree with what you have taken from the concept completely, and I view it in much the same way! I am sorry if this post seems pointless, but when I saw this page I just felt an impulse and acted on it.

Keep the tag alive.

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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Oct 29, 2008 6:49 pm

Talk about Mercury in Retrograde. I was forewarned somebody from my past would contact me now, but I would never have thought it would be you.

If you get back this way, PM me. I'd like to talk more to you (I still do not know your name) ... and see your animation again.

Thanks
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Re: dynamic modeling of a strip valve

Post by WebPilot » Sun Nov 02, 2008 2:25 am

Here is one result from my Mode 1/0 thread that is pertinent to this thread.

The reader will find the Barton spreadsheet that I programmed at this location on my Mode 1/0 thread.

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Re: dynamic modeling of a strip valve

Post by WebPilot » Tue Nov 04, 2008 5:23 pm

I wrote the present code in the spring of this year and always planned to return to it and 'have another look at it'. I agree that it shows 'qualitatively' what is going on - that valve behavior is dictated by driving frequency ratio, w/wn. In that respect, I am very pleased with it and plan to keep it 'up on the board'.

However, I now plan to use the model 'quantitatively' and am looking at it in a different light.

What bothers me now about that code is the following:
  1. the curve p23 is a constant throughout my plots.
  2. since p12 = Psource - p23, the curve p12 is also a constant.
  3. why were the pressures not following the opening and closing of the valve (the theta curve) ?
I realized from the beginning, the equations of my model should be what is known in engineering terms, 'coupled'. Mine were until that feature 'dropped out' while doing some algebraic manipulation. Go figure! I have now found a programming 'gliche' and here is the first 'glimpse' at the result of my modification.

I do not believe that this is 'my the last word' on the subject, but the present model is beginning to make more 'engineering sense' to me.

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Click here to see the entire image.

Interesting things about this plot:
  1. the curve p23 is now changing with valve position.
  2. p12 + p23 = Psource at any time, as before.
  3. p12 still has the familiar dip shape as before, but slightly lags valve position.
  4. for this dfr, 0.59, the valve closes at exactly the end of the -tive part of the cycle.
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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Nov 05, 2008 1:20 am

I am not sure what this model will show for an increase in driving frequency ratio. So, why not be my copilot and let's take a "look - see",
shall we?

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For w/wn > 0.59, the valve is beginning to stay 'open' in the +tive pressure regime. This, of course, is unsatisfactory behavior unless you like 'flames' blowing past your valves and coming out of your inlet.

Let's look further ...
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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Nov 05, 2008 1:37 am

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Here, you can actually 'see' the pressure, p12, the pressure across the 'circular orifice', actually becomes +tive before the valve closes!
Blowby!

I like what this code is showing me, so far.

Let's look further ...
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Re: dynamic modeling of a strip valve

Post by GRIM » Wed Nov 05, 2008 2:13 am

Forrest, this is amazing stuff ,
I understand that this is the box model and not a true combustor model, but if my current engine was a "box engine " I would be at about w/wn=1.1 , OR WORSE,

Eagerly awaiting the next instalment,

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Re: dynamic modeling of a strip valve

Post by WebPilot » Wed Nov 05, 2008 6:09 pm

Hi GRIM,

At the start of the thread, I have used a pump. What usually comes to mind is an air compressor, driven by an electric motor. Well, any pump will do.

It is my long standing opinion, that pulsating combustors and pulse jets are merely thermodynamic pumps. They are heat engines, and thus, their theory of operation will yield to a thermodynamic analysis.

continuing ...

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As w/wn increases beyond 1.0, the valve begins to operate in a manner 'counter' to what we desire it to do. That is, the valve opens when the amplitude of the driving pressure, Psource, is +tive!

Look at the pressure drop, p12, across the 'orifice'. It is almost fully developed when the driving pressure is +tive! This pressure drop is also +tive here. So the majority of the flow through the orifice over one cycle is going out not in!
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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Nov 06, 2008 6:21 am

I am going to show the response at w/wn=0.59 here, again. I like this one. The valve and resultant flow are very well behaved.

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Now, what happens when the dfr is below this value?

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Here the valve closes prematurely. The maximum pressure amplitude of p12 is the same, but the amount of time the 'pulse' is open is less than before. This results in less flow per cycle.

Decreasing w/wn further ...

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The amplitude and duration of p12 are decreasing even more than before. The valve began to close, then stopped at some theta, opened a little more and then finally closed in the +tive region of Psource. There appears to be no blowby.

Notice how the shape of p23, the pressure drop across the strip valve opening, at its apex has changed from the earlier plot. The peak has moved from the left side to the right.
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Re: dynamic modeling of a strip valve

Post by WebPilot » Thu Nov 06, 2008 2:42 pm

The wigglies are back.

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Here, the valve is opening, reaches a maximum value, almost closes, reverses direction and opens again, then finally closes. The pressure drop, p12, follows this valve behavior. Thus, so goes the flow.

Since the time increments are dissimilar for these plots, the value for total flow per cycle is hard to estimate for this one. It will have to be computed.
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Re: dynamic modeling of a strip valve

Post by Graham C. Williams » Fri Nov 07, 2008 12:19 am

Dear Forrest.
Wonderful stuff.
Is it possible to see the response of the valve (&p12) when the exciting pressure in the box (Psource)is offset in the +ve direction, say about 0.5psi?

Graham.
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light. Productions begin.
Now open your eyes.

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