Making a Tripwire

[ericvw]

I don't see a link to the video.... Curious about your results, tho.
EVW

[dpottier]

Aug 8, 2014 20:20:57 GMT -8 ericvw said:

I don't see a link to the video.... Curious about your results, tho.
EVW

What browser are you using? I have checked with FireFox, IE and Chrome and can see the video clip box in all three.  I have edited the post and reduced the size of the video by more than 50% (25 megs now) but kept the AVI format. Here is a direct link to the vortex generator test video. Hope this helps.

[ericvw]

Dpottier,
I got the vid to play.... Neat animation. Are you thinking of implementing this shape? Cant wait to see THAT!
Eric

[dpottier]

Aug 3, 2014 0:18:03 GMT -8 peterberg said:

Maybe it will work, maybe not. I've tried several trip wire setups, the one with the best results was facing down the other way. But please, build it, test it, and show your results. I like good ideas, especially when tested thoroughly.

Peter


Here is the video of the tunnel test results for the "Schauberger Vortex" Concept Insert.

We used two styles of insert. One with a hard 90 degree leading edge and a second with a chamfered leading edge. The idea being that a chamfered leading edge would prevent / lower the oxidation / eating away of the insert's material.  BIG surprise - chamfering prevented the vortex generation.

If you can provide the measurements of your tripwire we can try to model it and tunnel test it.

David

[dpottier]

Aug 10, 2014 8:14:19 GMT -8 ericvw said:

Dpottier,
I got the vid to play.... Neat animation. Are you thinking of implementing this shape? Cant wait to see THAT!
Eric

We use software to design and test a prototype way before building it.

In the example below are angles of 10, 20 and 30 degrees, from the insert's circumference, with same diameters. The right side has two different diameters (to be tested).
To build and test each configuration to get the best vortex generation would be hot, time consuming and costly work.

Creating and testing prototype designs using software makes life much easier when thinking about "what if" scenarios. :-)

• What if each slot was identical? 
• What if each slot was at ?? angle?
• What if we vary the distance from the circumference?
  
• What is each slot changed by 5 degrees or 10 degrees from previous slot in the vortex generator?
• What if ......
  

Having fought my fair share of forest fires and seen more than one fire tornado a recent documentary turned on a concept light for this configuration.
Some design time and a tunnel test was proof of concept. Now only the stack of "what if ...?" needs to go through the process.
Finally is it cost effective and practical for a DIY project. We license for commercial use but for individuals and researchers it is free.

This video clip will give you a proof of concept.

David

[peterberg]

David,
The purpose of the trip wire in the rocket heater tunnel is to introduce small eddies, just to disrupt the boundary layer and break up laminar stream along the ceiling. Any vortex will create drag as well, that's why I tried to keep it small. Larger vortices will create more drag so there's a trade off somewhere where the medication is getting worse than the defect.

All that aside, adding a trip wire to the combustion chamber had positive effects on the overall efficiency and appeared to add to a better burn. But that effect wasn't overly large, only in the region of 10 percent, maybe 15.

In short, the goal should be complete combustion rather than vortex generation or velocity.

Oh, my experimental stove consists of a 4"x4" duct, the trip wire situated about 30 mm from the feed at the ceiling, depth of the ridge about 5 mm, shaped as an arrow pointing to the riser with sides of 20 degrees.

[ericvw]

Hey dpottier,
That is some sweet software! Thank you for sharing. The various views brought me back to the days of Floyd laser light shows (at the planetarium)! Very impressive- but what will you do with it? I would like to see if such a thing could bring a positive effect to rocket operation, but when Peterberg says it'll add drag.... Still, it's some nice work and I say cut something out and fire it up! 
Eric

[dpottier]

Aug 11, 2014 0:41:24 GMT -8 peterberg said:

David,
The purpose of the trip wire in the rocket heater tunnel is to introduce small eddies, just to disrupt the boundary layer and break up laminar stream along the ceiling. Any vortex will create drag as well, that's why I tried to keep it small. Larger vortices will create more drag so there's a trade off somewhere where the medication is getting worse than the defect.

Hi Peter

I did not calculate the Drag Coefficient previously because the software used does not give me the ability to add all of the parameters, i.e. air temperatures inside the burn chamber. It uses 15C and 1.225 as the density. At the higher temperatures the density changes and so would the drag coefficient. That being said, below is a test calculating the drag with the tools available.  I hope you find it informative.

I will create a drawing of your tripwire using measurements provided and upload the results and will include the drag info this time.  :-)

Looking at the curve in your molded burn chamber it looks a lot like the type of curve curve Schauberger used. For molding, you have a great resource in the Netherlands. How close are you to the Delft factory?

David

[dpottier]

Aug 11, 2014 0:41:24 GMT -8 peterberg said:

Oh, my experimental stove consists of a 4"x4" duct, the trip wire situated about 30 mm from the feed at the ceiling, depth of the ridge about 5 mm, shaped as an arrow pointing to the riser with sides of 20 degrees.

Peter

I have modeled, tested and recorded your tripwire design from both side and top views and in the following configurations:

• 0 degrees
  
• 
  
• 10 degrees
• 
  
• 20 degrees
• 
  
• 30 degrees
• 
  
• and 20-30 degree angles left and right
• 
  

I first tunnel tested just the tripwire brick and realized a great deal of what was being seen was a cascade effect over the edge of the brick but it did show the vortex patterns.

I added 2 more bricks after the tripwire brick to get more realistic idea of what was going on downstream. (below is the 20 degree)

One thing caught my eye in the last tunnel test in side view of the 3 brick setup. The stiction effect, that is, the air flow running in reverse at the brick surface. When I get the videos assembled I will add a caption to draw your attention to this effect.

David

[peterberg]

Aug 12, 2014 15:51:33 GMT -8 dpottier said:

For molding, you have a great resource in the Netherlands. How close are you to the Delft factory?

I am living at the edge of Delft, it's possible to walk there. But what do you mean by Delft factory?

[peterberg]

Aug 13, 2014 23:37:49 GMT -8 dpottier said:

I have modeled, tested and recorded your tripwire design from both side and top views and in the following configurations:

The configuration is correct, the angle could be 20 or 30 degrees, not much difference. According to some reports I read, the tripwire works best at an angle to the stream. But in the burn tunnel there are sides as well, wouldn't it be wise to implement those as well in one form or the other?

Aug 13, 2014 23:37:49 GMT -8 dpottier said:

One thing caught my eye in the last tunnel test in side view of the 3 brick setup. The stiction effect, that is, the air flow running in reverse at the brick surface. When I get the videos assembled I will add a caption to draw your attention to this effect.

I've seen that mentioned somewhere, but of course I didn't know whether or not this was happening behind the tripwire. What would be very interesting: the effect of variations in the height of the trip wire. Is the stiction effect smaller or absent with a lower or higher ridge? And is that effect considered good or not?

Besides, implmentation of the tripwire is only one of the many factors into play inside my J-tube.

[dpottier]

Aug 14, 2014 0:18:49 GMT -8 peterberg said:

Aug 12, 2014 15:51:33 GMT -8 dpottier said:

I am living at the edge of Delft, it's possible to walk there. But what do you mean by Delft factory?

The Delft Pottery factory. I think it would also be a nice row or a sail from your home to there. Possibly, if the canals freeze, a wonderful skate in winter with a thermos of Bensorp chocolate and some fine cheeses.

David

[dpottier]

Aug 14, 2014 0:43:17 GMT -8 peterberg said:

The configuration is correct, the angle could be 20 or 30 degrees, not much difference. According to some reports I read, the tripwire works best at an angle to the stream. But in the burn tunnel there are sides as well, wouldn't it be wise to implement those as well in one form or the other?

I agree, all areas of the burn tunnel should have something to deal with the laminar layer.  I have a couple of thoughts that might work. One is to "dimple" the burn chamber like the surface of a golf ball, the second would be to add alternating rows of half spheres.

Using silicon to mold an acorn nut then filling that mold with fire or refractory clay and simply tapping it on a brick surface to release it would be cheap and fast. You would have to wet the brick first to help the clay to stick to the surface then let it dry before the first lighting.

A third option, taken from the swimsuit technology that has just been banned from competitions after more than 100 records were broken, is the modified shape of an Erlenmeyer flask. Large end towards the airflow. This could be made using a 5 mm plywood such as Baltic Birch and molding the pattern with silicon rubber then using fire clay as above. Using your 4 " burn chamber, two 1.5 or 1.75 inch wide patterns and placed side by side would be interesting to test if the "tunnel" results look good. It would also give a wider area of air disturbance. The current 20 degree angle gives only a single point which I think deals mostly with the central area of the burn chamber.

Let me model it and see what the results are.

I've seen that mentioned somewhere, but of course I didn't know whether or not this was happening behind the tripwire. What would be very interesting: the effect of variations in the height of the trip wire. Is the stiction effect smaller or absent with a lower or higher ridge? And is that effect considered good or not? Besides, implementation of the tripwire is only one of the many factors into play inside my J-tube.

I can easily change the tripwire heights and test them. Modeling the first brick with a 20 degree diagonal, left to right, and a second brick with a 20 degree angle right to left can be tested. Arcs instead of angles are possible as well. In the real world slicing an old broken Delft tile at 20 degrees and rounding (grinding) the leading edge then cementing it inside the burn chamber would be a cost effective solution. Heavier floor tiles would give an increased height but not sure of what cone # they are fired at.

I was a professional Life-Guard and White Water Kayaker. In river or rapids rescue we take advantage of stiction to easily move upstream as the water near the shoreline moves in the opposite direction to the flow. The faster the rapids the greater the stiction so I will assume that increasing or decreasing the height and hence the turbulence would have a similar effect as water and air are both fluids.

David

[ericvw]

Hey dpottier,
    I, for one, like your analogy of white water kayaking. Having grown up on rivers both fresh water and tidal, I remember experiencing this effect myself. I believe in the fluidity of different mediums, sharing similar flows and such. Please keep the thinking and software simulations coming... I do agree that simulation is more cost effective than multiple experimental(and costly) builds, but we must consider the efforts of all in this forum, especially peterberg, and the indispensable effort and posting they have contributed. I am certainly appreciative, and I know many more are, too. That being said, this use of software is VERY intriguing; please continue to post results and videos! I love videos as much as the next rocketeer!
Thanks for sharing your work David,
Eric VW

[Daryl]

I do like your posts but can't wait for a real world trial. I am curious to learn about buoyancy, pressure, and energy with your model.

P.S. Kayakers rule!