[CraigD]

Originally Posted by Qfwfq

I also have a vague memory, from some 30 or so years ago, of a missile design emloying a small, flat circular plate to create a shock wave all around the craft. I imagine it reduced drag but ran into various engineering troubles.

This sounds a bit like the “aerospike” found on compact missiles like the US’s sub-launched Trident. From what I’ve read, the feature was successful, and did good things for the performance of the missile (if “good” is an appropriate term for a nuclear weapon ) They’ve been around since the late 70s, and, according to the wikipedia article, are expected to be around past 2020.

[Qfwfq]

Trident could be it, yeah.

[Turtle]

I have started...er...picked back up construction of an experimental laminar flow fan duct. This is not an engine for any propulsion , rather a tool for experimenting with the effects of low velocity laminar flow in air.

In this video I show the duct during the installation of the first row of straws. When complete, the duct is fully packed. 12Volt auto fan, coffee can, drinking straws, masking tape & the cow's glue everyone knows & loves. Just keepin' it cool.

YouTube - Laminar Flow Fan Duct Construction

[freeztar]

Originally Posted by Turtle

I have started...er...picked back up construction of an experimental laminar flow fan duct.

Can you explain this in detail Turtle? The video didn't clarify it for me.

[Turtle]

Originally Posted by freeztar

Can you explain this in detail Turtle? The video didn't clarify it for me.

All the 'splainin is to follow of course, but it did occur to me that maybe I should have started a new thread in the Science Project section. Feel free to split this off if you think it better.

To summarize, imagine you have a lighted candle, and the fan as it comes. If you use the fan to blow out the candle, there will be a maximum distance between the 2 where the fan no longer blows out the flame but only wiggles it.

Now all else being equal, that is not speeding up the fan or using a different one etcetera, what can we do mechanically to increase the distance from which we can blow out the candle?

My hypothesis is that placing a duct packed with cylinders will achieve that aim, and by an impressive amount. The principle that accomplishes this is laminar flow, and rather than modifying an object moving through air, here we are modifying air to move through air, or as the title has it, we are going to lubricate the air itself.

While the glue is drying I'm considering if it's worth building a small wind tunnel? Off to check the glue and cut some more 4" sections of straws. ...........

[freeztar]

Uber-cool Turtle!

So are you just lining the inside edge of the cylinder, or are you planning on filling it in with more straws?

I'm still uncertain about how the laminar flow is occurring in your model. Is it just because the straws isolate the air flow and hence reduce drag? Or is it because the straws create a much higher pressure?

[Turtle]

Originally Posted by freeztar

Uber-cool Turtle!

So are you just lining the inside edge of the cylinder, or are you planning on filling it in with more straws?

I'm still uncertain about how the laminar flow is occurring in your model. Is it just because the straws isolate the air flow and hence reduce drag? Or is it because the straws create a much higher pressure?

The edge lining is just the first layer, and the entire cavity is ultimately filled yes. I decided to make a video showing the construction steps, as when it is done it may not be obvious how it is made.

I have conducted similar experiments on a smaller scale, and I do know this arrangement is how those jumping fountains produce a cohesive laminar flow stream with water. I don't want to hastily jump into an explanation of how/why it works before I have a proper understanding of it myself, but I know it does work and I want to demonstrate it while I explore some aspects of the effects that I am personally curious about. I am not aware of anyone else doing this, but I'd love to learn of it.

I have had to settle for certain conditions I would avoid if I was engineering this under an unlimited budget. For example, I would make the duct the same diameter as the fan and in my machine the coffee can is smaller and so I have some backpressure developed from the venturi effect at the constriction. I expect this effect, and the additional backpressure from the straws, to have a negligable effect on the laminar flow exiting the duct.

It would be nice to besides tests using first no duct, and then the laminar flow duct, to include an empty duct, but my construction methods have excluded that option. I note that with my small scale experiments, an empty duct adds little if any distance to the candle flame blow-out standard. The empty duct is afterall very much the same principal as is well measured and even in use with propulsive fans as we have already discussed here.

I can run on, but I'll stop here. Perhaps someone would like to calculate the ratio between the cross sectional area of the straws over that of the inter-spaces formed between them. (Hint: no real measurements are needed for this calculation; it is a close packing problem.) .......

[Turtle]

Alrighty thens. While you work on that close-packing ratio solution (which may matter if we wish to calculate the cross section of active duct because many of the inter-spaces are closed off by glue), I have finished up the first ring of straws in the duct. While I have used the term 'straws', 'cylinders' gives a better geometric picture, and each is in fact a duct itself. We are building a duct of ducts. Quack, quack!

I did the control run this morning and will have the video presently. The open fan can blow out my test candle from ~ 7 1/2 feet away. I have the first row of straws in place, and I see now I can do a ducted blow run after each row. With this first row, it should be a close approximation to the empty duct.

Now that we have all our ducts in a row, it's time for lunch. Smoke 'em if ya got 'em.

[UncleAl]

Kinetic Temperature, Thermal Energy

Mach 20 = 6806 m/sec. For air with average molecular weight = 29 daltons, Mach 20 gives 80,000 C (most probable speed) to 52,000 C (RMS speed) as the apparent relative temperature of the surrounding atmosphere. What difference does surface "lubrication" make when sitting in a plasma furnace?

[alexander]

ooh i wonder if i could make a prototype for this for a car, obviously paper straws are out, but i am wondering if and how much it would increase the amount of air that is pushed into the engine by streamlining it's motion.... perhaps this would be interesting with a turbo?