Wheel with dawn

[Grelinette]

Hello everybody

I just read a silly but interesting mechanical question on "the positioning of a paddle wheel":

Where to place the axis of the paddle wheel if you want the best mechanical power?

As close to the surface of the water, or on the contrary,
distant so that the water exerts a force only on the ends of the blades?

This question interests me because it joins the principle of vertical wind turbine blades which could benefit from a partial fairing as we are starting to see some of them,

or formerly as were the "Persian mills"

(nb: this question comes from a science site, and by correction I would put the link or the answers)

[dede2002]

Hi grelinette,

hot I would say the axis closer to the water, all energy is good to take.

Then it will be necessary to calculate the circumferential speed ...

[Macro]

It will mainly depend on the speed of flow of the water ... but to know the bigger your impeller will be the more it can have blades in contact with the working fluid so it can have more torque (and if in addition the lever arm increases) on the other hand the speed of rotation will decrease ...

[sen-no-sen]

Where to place the axis of the paddle wheel if you want the best mechanical power?

As close to the surface of the water, or on the contrary,
distant so that the water exerts a force only on the ends of the blades?

If you want to recover a maximum of power you will have to place (- for a paddle wheel with vertical blade -) the blades in contact with the surface of the water, it is for this reason that the paddles of the wheel paddles are generally 1/4 to 1/5 the diameter of the assembly.
Otherwise the drag would greatly slow down the structure.

[chatelot16]

all depand what wheel has dawn!

there are many completely different principles

your Persian mill is wind: this principle cannot be used in water

for high falls there is the bucket wheel: tree at half the height of fall ... the buckets are filled at the top and empty at the bottom: the performance and good if it is very slow ... the faster it goes the more the yield decreases because the kinetic energy is not managed correctly

wheel below: this is the type of wheel that there is in small mills around my house: a more or less open valve lets pass a jet of water, which taps at the bottom of the wheel: horizontal axis well above the level: the output is shabby like 20% because the impact against the wheel is done anyhow: this wheel has a more modern version: poncelet wheel: efficiency as good as a turbine like 60%: curved blade : the jet leaving the valve is deflected by tapping in the curved blade of the wheel, then is deflected a second time by the curved blades to exit the wheel

most recent: sage wheel or valve wheel: very large diameter wheel rotating very slowly in a very well-adjusted steed: water cannot pass between the steed and the blades ... large number of blades so that if it there are leaks the water must pass the leaks of all the dawn which is in the courier: the sagebien wheels have an excellent performance better than the turbines but turn very slowly, must be very large to make power, larger that the poncelet wheels

there are also the spoon wheels of small mills in the mountains: exactly like the peleton turbine: very good performance