Laminar Fountains – What are they?

My first working laminar fountain

My first working laminar fountain

Water water everywhere! There are no two ways about it, water fountains are just plain fun. Show a water fountain to any five year old and just see if they don’t start playing and giggling. Which leads me to this conclusion: I never grew up because I still get a ridiculous grin on my face when I get to play in a water fountain. And the coolest of all the fountains in my opinion is the laminar fountain. I built a laminar fountain a few years back and am now working on designs for a 3D Printed laminar fountain which I will post online once I get a semi-working alpha version. In preparation for all that let me explain a little about what laminar flow and fountains are.

What is laminar flow?
The simplest way to explain laminar is probably to say that it is the opposite of turbulent flow. Turbulent flow is the most common type of flow you will see in nature. A drinking fountain is a good example of turbulent flow with how blobby and wiggly the water is when it comes out. White water rapids in a river would be an extreme case of turbulent flow. So in contrast, laminar flow is super smooth flowing liquid or gas. The full reality of laminar flow is that it means all of the water particles are flowing exactly parallel to each other, in the same direction, and as such are not bumping in to one another.

Laminar flow profile showing the velocity of water as it moves through a pipe. (Taken from wikipedia)

Laminar flow profile showing the velocity of water as it moves through a pipe. (Taken from wikipedia)

Laminar Stream

Real world picture of a laminar water stream after it exits my laminar fountain. Because the water is all flowing in the same direction it stays perfectly together and creates a glass rod effect where light can pass right through.

So why it cool?
Because it’s science! But also because it has some really cool application properties we can make use of:

1) Its moving… buts it doesn’t look like it
Because a laminar stream is perfectly smooth the flow path will stay in exactly the same place at all times. A traditional fountain will wobble and sputter as it pumps water out which makes it very obvious that the water is moving since you can follow the individual water blobs as they pass through the air. A laminar stream is perfectly uniform and does not waver which means there are now individual water droplets to follow with your eyes. The water is flowing quickly but its hard to tell. It literally looks like a perfect glass arch coming from the fountain going all the way to where it hits lands. (See the picture above)

2) No splash
Because the water stream is so smooth it will not break apart when it encounters another body of water or smooth object. If it lands in a pool of water it will disappear without a trace. If you put a smooth ball in its way it will spread out and wrap around the ball without splashing. Its a really cool effect and also has the benefit of making it quiet too!

3) It Jumps
Because the flow stream is so smooth it has a nifty visual effect when you suddenly block the stream. It looks like the stream is “jumping”. The water that is not blocked continues to fly through the air on the original path and stays together. You get little water snakes that that fly through the air. If you string multiple fountains together you can create the illusion that water is jumping from one fountain to the next.

4) It transmits light like a fiber optic cable
A fiber optic cable is a perfectly smooth medium that transmits light from one end to the other. The perfectly smooth sides of the cable reflect the light inside back in to the cable to keep it bouncing down the length until it reaches the other end. A laminar stream also has super smooth sides and therefore will also bounce light back inside of itself. This means that if you shine a bright enough light directly in to the laminar stream it will light up all the way from end to end! Even around the curve!

Here is a cool video that shows the laminar fountain forum user MagicNozzle posted of his home made fountain that demonstrates several of these properties (feel free to skip ahead, the night shots at the end are especially cool). Original forum post HERE

Laminar Maths:
If you’re in to math and the equations that govern when a stream is laminar than this is the section for you. I find it super cool how this works so lets dig in!

In an engineering fluid dynamics class (study of moving liquids, a really fun course) you learn about the Reynolds number which will tell you if a fluid’s flow is laminar, transitional, or turbulent. Here is the equation from Wikipedia:

AHHHHHH!!!1!1!! Maths! *Deep Breath* This equation is actually super simple so hold on and keep reading.

AHHHHHH!!!1!1!! Maths! *Deep Breath* This equation is actually super simple so hold on and keep reading.

Hold on, we’ll kick that scary equation in the teeth. Lets start by focusing on the first variation of the equation listed.

Re = (p*v*D)/u

Two of those are actually constants. p is the density of water which we can google (1000Kg / m^3) and u is the dynamic viscosity of our fluid (water is 0.000404 at room temperature). So putting those back in and simplifying we get this:

Re = (2.475×10^6)*v*D

That’s not so bad. v is the velocity of our fluid in the pipe in meters per second and D is the internal diameter of our pipe in meters which should be pretty easy to calculate. Once we have our Reynold’s Number (Re) we can see if the flow will be laminar. An Re value below 2300 means that the flow is Laminar. An Re value between 2300 and 4000 is Transitional and an Re value above 4000 is Turbulent. All this means that we need to adjust our water velocity and pipe diameter to get an Re below 2300 for our fountain. That’s all the math!

How the math works in real life:
So now that we have the math (or trust me if you didn’t read it) we can interpret it. This is what it all boils down to in real life:

The faster the velocity of the fluid and the bigger the pipe, the more turbulent the flow will be.

Or inversely:

The slower the fluid and the smaller the pipe the more laminar the flow will be.

So to put this in to the real world lets tackle one problem at a time and start with velocity. We need a certain minimum amount of volume flow to achieve the fountain size we want. For instance, the pump I used in the pictures above is rated at 500 gph (gallons per hour) which gave me the nice big water arch you see. The problem shows up now in that the velocity is found by dividing the flow rate by the cross sectional area of the pipe which is a function of pipe diameter as well! So we need a bigger diameter to slow the velocity down but a smaller diameter to get a low reynolds number…… Crap.

But what if I told you we could have a separate diameter to use for velocity and the diameter in the Reynold’s equation? The trick is to take a large pipe (8 inch PVC here) and pack it full of small pipes (drinking straws). This way you get to use the large diameter of the PVC  for the velocity part and the small individual diameters of the drinking straws for the Reynold’s diameter. Bingo! We can now achieve laminar flow!

Inside my laminar fountain are nearly 2000 drinking straws to give a small diameter to the water flowing through while keep the slow velocity of a big 8 inch outer pipe.

Inside my laminar fountain are nearly 2000 drinking straws to give a small diameter to the water flowing through while keep the slow velocity of a big 8 inch outer pipe.

Theory crafting complete!
That’s it for the what a laminar fountain is. Stay tuned for some more posts talking about my first laminar fountain and how I am hoping to use my 3D Printer to start a new cycle of designs!

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11 thoughts on “Laminar Fountains – What are they?

    • I actually purchased that from a guy on the forums at http://laminar.forumotion.com/ Its a small copper disc that was turned on a lathe. He found a website where you can put up small parts for machine shops to bid on to fill their down time. I really wish I knew which site that was as I would love to get my own run. I’ve been meaning to go back and do some research on that. I’ll see what I can find out

      PS I’ve also 3D Printed some nozzles now and while they do work decently they aren’t quite the same caliber as the machined ones I have.

  1. I had a 500 GPM rated pump and accounting for head pressure losses I think I achieved roughly 60% of that as real world output.

    • Thanks. One other question which might be a little odd. How much noise does the stream of water make when it encounters its destination? Negligible? Super noisy? Somewhere in between?

      • Its really quiet actually. The deeper the collection pool at the end the quieter as there is less rebound off the bottom which can lead to turbulence. If you want whisper quiet you can put a piece of foam at the end where the fountain stream hits. Not only does it dampen the small amount of noise but it ensure zero splash back (you get a small amount of splash when going directly in to a pool if the pool has a choppy surface) The pump was by far the loudest part of my build and its really pretty quiet itself when submerged.

  2. Hello Isaac, I have built my first Laminar flow nozzle from 4″ PVC. The water first goes thru a 2″ thick open cell sponge, then thru full length drinking straws (a screen on each side of the straws), then I have 2″ of air pocket, then exits thru a 1/2″ hole. The hole is counter sunk and a used a bit of sand paper to smooth the edges. I’m using a 400gph eco plus submersible water pump.

    Here is a video of it running:

    As you can see, my water stream starts to wobble and then break up about 1/2 way thru the arc. Do you think my exit hole is no good? Or could it be the water pump is not pumping consistently? Thanks for your help.

    • Hi Tom,
      A couple things come to mind. One would indeed be pump jitter. But that can be solved by adding a low pass filter. That is basically a piece of PVC stood on its end with an inlet at the bottom, an outlet just a little ways above that, and the top end capped off air tight. What that does is trap a pocket of air at the top that acts like a spring to absorb the vibrations. That can help greatly with pump jitter. Here is a link to a picture from the laminar fountain forum of what one looks like http://i468.photobucket.com/albums/rr42/liteglow2000/airtank.jpg

      You may also want to consider adding a small air release valve to the top edge of your fountain. When fountains are tilted they can get air bubbles trapped inside that hang out behind and above the exit nozzle. Sometimes these can effect the quality of the stream. The two ways to deal with this are 1) to tilt the fountain straight up and move it around to get the air out the nozzle or 2) put a small pin hole in the top edge just behind the end plate to bleed air out and then plug up during operation.

      The final thing I might look in to is to put something in front of the inlet at the bottom to swirl the water around a bit. Having the water come straight in can sometimes cause different pressures in different areas on the filter foam which causes changes in flow speed. Diverting the water from the inlet to the side or split two ways can help break up some of the inlet pressure and even out the flow through the filter foam.

      Hope that helps! If you want to start a post at http://laminar.forumotion.com/ you can post pictures and things there to get a bigger discussion going. Otherwise keep me in the loop and I’ll do what I can to help!

  3. I’m struck with calculations of my Flow rate and head pressure losses, can you please help me with that?

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