Aerofoil underwater

Daiquiri -- PIKE FISHING --AAHHhhhh someone is trying to catch me on a hook--

 

Ideally, pulsating flow.
If thats not possible then Turbulent flow.

I am not sire how th flap idea would work as the pressure from the pump is constant?

Let me just say thank you to veryone so far for looking into this

 

A pulsating flow can be created by using a piston pump instead of a rotary one, for example.

 

MMmmmm -- Place the snorkel injection before the intake of the pump and come up with a simple way to dip that snorkel hose in and out of the water and you should have a turbulant/pusating flow.----

 

It is quite possible to create a pulsing flow with no moving parts. Do a search for "fluidic oscillator". Basically what you do is have a bifurcated duct in which the Y part is steep enough to cause flow separation on the outer walls. From each output leg of the Y, you place a small pitot tube or inlet facing upstream, and plumb that to a hole just downstream of the branching point, that blows at right angles to the surface. Do this for both legs of the Y.

What will happen is the flow will more or less randomly go down one leg or the other of the branching duct. When it does, the small duct will act as a feedback loop, and the flow through the feedback duct will cause the flow to separate at that side of the Y. The flow will then switch to going down the other branch of the duct. This does two things - it cuts off the flow going into the first feedback tube, and it starts the flow through the opposite feedback tube. The new feedback causes the flow to separate on the new side and switch back to the original side. The end result is the flow oscillates between one output branch or the other.

If both outputs are plumbed to your aquarium, you will get a pulsing flow coming out of each tube, with the pulses alternating between the tubes.

If you only wanted one pulsing output, you might be able to plumb one output of the branching duct to be the feedback to the opposite side. I"m not sure what would happen in this case, as you'd have one output that was essentially dead-ended. It might alternately feed and then cut off the flow to the feedback duct and give you the pulsing flow you want. However, it might just settle down into a steady flow situation. I know that the two-output oscillator that I described above will work well.

It's a little known fact that it is possible to do nearly everything with fluidics that you can do with electronics, including logic gates, swtiches, amplifiers, etc. But the circuits are much heavier and slower, and take a lot more power. However, for some applications, especially in very harsh environments, fluidics are a very good choice. A good example is the original F-15 flight control computer, which was all hydraulic and was essentially a fluidic stability augmentation system. (They've since been replaced with a digital electronic flight control computer.)

 

Most if not all marine aquarium pumps are rotary.
I think creating a pulsing flow may be harder than I thought. Maybe I will have to have a moving part in the pipe somewhere?

 

WOW! that sounds like a great idea Tom. I will look more into this. I dont mind two outputs as long as there only one input(which your idea has).

Truely amazing what can be achieved with clever engineering

 

Can you modify the rotary pump and install a rotating orifice at the pump outlet? It could be connected to and moved by the pump shaft. In that way the flow would be alternatively stopped and let go, depending on the angular position of the orifice.

 

Pulse

Attachd is a quick image of what I think you meant. Is this roughly correct?
And this then creates a pulse effect?

 

Introducing air via a surface air tube through a small hole in the pipe will aerate your flow more than you could imagine.

 

It would ontroduce micro bubbles into the display which is no good for marine aquariums.
It seems the above idea is best I just wont to mak sure my vry rough drawing is grasping the idea correctly

 

Yes, that's basically what I was describing. The inlets of the feedback tubes should face upstream, though, so they get the maximum ram pressure to feed back. Like this:


There are other types of fluidic oscillator, but what they all have in common is a bi-stable flow situation with separation that is influenced by flow feedback. Here is another type of oscillator that may be more suited to your application because it has two inputs (which could both be from your pump) and one output that oscillates in direction.




And finally, here is another similar oscillator that produces a single pulsing flow, which may be what you want:


The literature on fluidic oscillators is vast and there are a great many different configurations. Not all may be suitable for your flow rates, so you will need to experiment a bit to find out what works best for you. The length of the feedback lines can influence the oscillation frequency, for example.

If you've ever used a pulsing shower nozzle, you've seen fluidic oscillators in action.

 

p.s. Here's a great Scientific American cover article on fluidic devices, including fluidic oscillators.

 

As fascinating as this stuff is, it mostly applies to gasses, really small liquid devices, and items with a pretty good pressure head. I think we need to look more towards a lava lamp than fluidics. It might be possible to exploit the Colandra effect and then deamplify the effect. If you want to experiment, try playing with flat hose- the type that rolls up flat on a reel. It is used for portable pumps and tends to "slug" at the discharge if run across the ground. I think you would need to run a loop above the waterline over a low wall, say 2" above wl, then let a foot of hose float on the surface. This should slug the flow. You can control the frequency and volume by controlling the hose volume and wall height. The general idea is similar to this, with gravity replacing the surface tension.

http://en.wikipedia.org/wiki/Plateau–Rayleigh_instability

its kind of like the noise a balloon makes when you let it go, only much slower.

 

Fluidic oscillators with a single input and an oscillating fan output are in everyday use as windshield washer nozzles on automobiles. Bowles is a major producer. http://www.bowlesfluidics.com/