How to Create a Funnel-Shaped Twister in a Tornado Machine?

[Meatball]

Hoping one will look nice in my new living room, I want one constructed about 7 feet high.

I think I understand the basics of how these machines work, but I'm wanting to change something.

Most tornado machines you see produce mini twisters that are shaped with parallel sides- to where the twister isn't even a funnel anymore.

http://www.youtube.com/watch?v=AYMfdchcASw&feature=bf_prev&list=WLE5754075D91FD0B3&index=26

Pretty cool eh?

So my question is, if I want a nice funnel shaped twister, do I want faster rotating air at the bottom of the twister? Or toward the top?

I'm not entirely sure how to linearly change the rotation speed of the air as a function of height, but I have one idea.

I haven't seen any machines that produce this effect, so I'm assuming it makes things more difficult. :P

I'm thinking that a larger diameter updraft fan will allow top funnel diameter to expand.

Anyone have ANY idea if I'm going to be any desirable results?

http://www.flickr.com/photos/62275796@N08/5660128324/in/photostream

Is increasing d a good idea?

There are PVC pipes in the four corners of the display case.

Air is forced into each of these pipes via squirrel fan. This air escapes through the many holes drilled along the height of each pipes. Each pipe is then rotated to where the force air from the drilled holes moves from one corner to the adjacent corner. This cause the needed rotation. There is a large fan on top of the device sucking air out of the display, causing the low pressure needed to draw the vortex upwards.

So how do I prevent a silly constant diameter vortex from forming? Should I vary the pvc hole diameters along the length of the pipes?

Larger holes may yield more air leaving the pipe at a slower rate, while smaller holes may yield a faster air escaped speed, but less air might leave the tube during each second..

Where is the draw off? Where is that line drawn?

 

[Navin A S]

When does the air leave the pipe in a way that will cause the vortex to be funnel-shaped? I think it's a combination of controlling the speed of the air, the direction in which it is leaving the pipe, and the rate at which the air is leaving the pipe. You want to create a balance between the rotation of the air and the speed at which it exits the pipe. The faster the air is exiting, the more narrow the funnel of the twister should be. The slower the speed, the wider the funnel should be.