I am Looking for a Passive Fluid Amplifier

Perhaps you can describe your setup a little more so we can all get a better picture of it.

Is the paddle that you are refering to part of a paddle-wheel? Or a motor-generator set?

I want it to generate electricity where I live , so need it to turn a shaft

Have no idea what your on about...You want some sort of souped up paddle for your dingy?

What about a drift chute?

I don't think it will work, it is a venturi, the speed of the water will be higher but the amount will be less so nearly the same amount of force will be available minus drag

wrong place oops

Wouldn't that be increasing the head?

Sorry but no. I did say you could not increase head pressure.

I don't think an impulse turbine would do any better but it does sound interesting please expand further

If you are looking to extract the most energy from a given flow with a sufficient drop, a good design using a well matched Pelton wheel (an impulse turbine) would be very difficult to beat.

Pelton wheels can be far more efficient than typical overshot wheels. The water is accelerated through one or multiple jets to about twice the speed of the paddle, then interacts with the paddle which changes the flow of the jet roughly 180 degrees and exits with minimal energy.

Correct me if I'm wrong, but I thought a Pelton wheel is best choice (most efficient) only for fairly high heads, a few tens of metres at least, as on full-scale hydro jobs. For low heads Francis or Kaplan turbines better.

If it's something like a traditional watermill or a DIY job, head is likely to be a few metres.

You are right. I thought that low flow high head were specified in the OP, but rereading I realize I imagined that all on my own.

A pelton wheel really only shines with sufficient head.

No. You can increase the amount of work done by making the paddles larger.

Or, you could increase the specific gravity of the water.

That will not increase the force of a give amount of water. Sorry I should have put that in as a requirement, my fault.

If you are using all of a given amount of water already then that is all you get. If you have more volume available then that is a different story.

Do a rain dance and get more water flow.

Sorry, that just increases head pressure.

True that flow and head may not be completely independent, but increased flow can happen with only marginal increase in head. Larger paddle area ≈ greater flow; not necessarily any increase in head.

Good Point but "it can't rain forever"

Is the paddle driving a boat through the water or is the river powering a standing generator?

You mean something like this gizmo...RIVER PADDLE WHEEL WITH 14" CHAIN DRIVE TO #SC12 PMA - 3000 Watts

Yes, but this paddle wheel design is just trying to use every bit of what is available. If the paddle wheel was the same width and depth of the stream it would still not give more force than what was already there, unless it forced the water to rise up and that increases head pressure.

I think maybe the same fluid dynamic principle that makes a sail boat go faster than the wind would do it....or

maybe by using the water to compress air in a large pressure tank half filled with water… with multiple sites and sequential timing <?>

Depending on location you might make a tidal tank thingy, where you capture a body of water at high tide and discharge it at low tide, generating electricity both ways.. Sailing uses the force of the wind against the rudder in the water, sort of like a bar of wet soap slipping out of hand...I don't see how that would apply here....

Actually sail boats use the keel much more than the rudder and the sail uses a venture effect unless it's ruining down wind. A paddle is like running down wind what I want do it beam reach where the sails are in full venture mode and the low pressure side is pulling the boat faster than the down wind run. That's why racing sail boats never run completely down wind, they jibe back and forth.

You can sail without a keel, try it without a rudder...

You can and I have, when I single handed my 23' sailboat I did not have an auto pilot. So, I would tie down the helm and adjust the center of gravity of the sails to be either in front of or behind the center of gravity of the hull including rudder and keel. This is simply done by trimming in out main or jib, which steers the boat in any direction I wanted.

Without a keel you will find very quickly that you can only go down wind.

whoups i didn't reached to that "®Slow or fast you can't extract more energy from the water than it contains." yet

so donno what the head preassure means coz nonenlish but if the rotor speed is an issue the moment I=Σmr² can be geared up with the gearbox (post err-chk done the subj may leave muh-hah)

® replacement

"®I think maybe the same fluid dynamic principle that makes a sail boat go faster than the wind would do it....or"

(i hate cascading errors - errors are the generators of NEW stuff however, so...)

"maybe by using the water to compress air in a large pressure tank half filled with water… with multiple sites and sequential timing <?>"

This sounds like the hydraulic ram that I mentioned in another response.

Thinking about it, Yes it does

You might benefit from the venturi effect if you turned the channel back on itself. I suppose it would have to be an "S" bend. The entrance wide, narrowing up around the bend into the following legs. Put a cross channel with the paddle in it, connecting the entry and return channels. Because flow is faster in the second channel you could get an effective suction on that side to help the pressure on the front side.

If the paddles were closely spaced, the cross flow would be small.

I don't know how much drop you have in your stream, if it is in the region of twenty feet or so you might adapt an hydraulic ram

But if the paddle is still in the inlet side would it not slow down the second channel? Or do I have your idea wrong?

I now realize that the idea is impractical, or even wrong, what might work in a closed pipe system won't in an open channel system. In moving from the wide channel to the narrow channel the surface of the water may rise instead of speed up, thus losing the difference in pressure.

The thing is, the energy of the flow through the inlet is almost all kinetic already, and it is the conversion of the potential energy to kinetic that reduces the pressure.

If your paddle blade will fill the channel, there isn't much more you can do. If it doesn't you can improve efficiency with shapes. A double concave cross section would be best, on the inlet side it maximizes pressure and on the outlet side it maximizes negative pressure on the blade.

YES, and that where I am trying to go, but I lack the necessary knowledge. I am hoping to get enough incite from this discussion to overcome this temporary lack of brain power.

We seem to get that a lot here eh....

I just saw a passive fluid amplifier, but all it did was make more passive fluid which didn't do anything, so I let iit run off.

Thank you for my smile this moring

but I would rather keep trying to figure it out. Life long learning....

Just a new thought, you are using paddle wheel thinking when a nuke sub's prop is a lot closer to the task at hand. No cavitation, just raw power and all the technology our scientists can think up. We have come a long way from riverboats.

Thanks for the push.

I think things are getting stale on this idea.

Actually, a propeller generates the same sort of lift force that a sailboat's sail does. (A propeller is a set of twisted wings). 50% conversion efficiency is about tops for a propeller, although a duct through which all the stream's water flows improves this. Follow this line of thinking and you end up with a hydroturbine.

The Pelton wheel (in which a nozzle increases water speed and directs flow at little buckets) can be about 90% efficient, remarkably. Nothing you can do will improve that to 100% (with a Pelton wheel or any other means for extracting energy from water).

The stream is flowing so you must have some head available. You are looking for a solution to increase energy harvesting based on the water flow, maybe you should be looking at utilising the water weight. A practical solution is to prevent any of the water from bypassing the paddle. As already stated you cannot get more energy out than is contained within the water without adjusting the available head. So to maximise output you have to use ALL of the water and ALL of the head. A 'paddle' suggests that some water is flowing around the sides taking some of the energy with it.

Dig a hole in the stream bed at the downstream boundary of your property. Install an overshot water wheel. Starting at the upstream boundary of your property, install a horizontal flume that terminates in a shoot directing ALL of the available water onto the wheel buckets. The flume puts ALL of the available head in one place where you can utilise it.

I do not claim any expertise here. If a Pelton Wheel (reply 28) is more efficient than an overshot wheel, substitute Pelton Wheel into my previous answer. You still need the flume to concentrate the head but terminate it in a restricted bore pipe to increase the water velocity.

Fluid Amplifier is not the right term. A fluidic amplifier is a fluidic device that acts like a transistor where a small fluid flow controls the path of a more energetic fluid flow. Like a transistor, it doesn't result in any increase of energy.

I think what you probably mean is "What is the most efficient design for a paddle wheel to extract energy from a stream?".

the sailing stuff where the side wind boosts the ship faster than the wind speed - there are two force vectors combined <=> (speculating:) the wondering shaft turbine might get the systems bound ... donno (it's 12:23 AM - and i'm scheduled for different suff right now) . . . the fluids dynamics (is differential 3D vector matrix) and the conservation of E-laws ... it takes to play around

:::::\....... ? underwater dams () spoilers ... e.c.

i'll skip to my electrical circuits section for what i registered actually :P

A fluid amplifier is nothing but a valve, whose setting is controlled by small variations in pressure. Such an amplifier would be useful to allow more or less water to flow in response to more or less pressure on the actuator of the valve.

A toilet tank comes to mind. Uses negative feed back from the height of water in a tank to control a valve which controls the height of water in the tank.

Thats what an amplifier does....something which uses a small input to control a large flow. The pressure head in a toilet tank is minisule compared to the pressure in the supply pipe, you HAVE to admit.

I think that's called a regulator,

A transistor or FET are such valves but they are supplied from the outside power supply.

I don't see where the power supply is coming from in my stream.

A big rock placed at a certain point should force the water in the river towards the point you wish to increase flow but it might take more than 1 rock. The water flow should be albe to flow over the rocks when the water level rises from rain.

You asked... is there a way of increasing the force of a river against a paddle without increasing the head pressure.

Yes.

You can use a bigger paddle.

A venturi should work if the outlet width equals the width of the paddle and the upstream opening is wider.

Wrong way round! If velocity increases, pressure decreases.

Thank you Pass