He should tie a string to the boat
The string should show as dragging behind the boat, indicating there is current moving against the boat in the area where the boat is. If the string wiggles in the same direction as the boat is moving, than the experiment is no good…
Just like the ribbons on the “faster than the wind” video that I posted show the point where the land-moving sailing vehicle begins to exceed the wind speed thus proving in practice one can exceed the wind speed directly downwind (and that video has been officially certified to be “real”).
String?
– Last Updated: Mar-12-12 6:39 PM EST –
I don't think is is a good idea.
By nature - If one is working on fluid dynamic he/she should concentrate on the coming current, the flow in the back are very much driven by turbulence (eddy is a kind of turbulence too).
Thanks
yes, need actual flow, not a jet in a cl
Need a real flow and not a jet in a closed tank. Need a flow tank. Like an oval track. In such a tank the flow goes around the circuit. In a rectangular tank with a flow coming from one end and no outlet there will always be a return flow.
A close tank?
– Last Updated: Mar-12-12 6:55 PM EST –
The water comes from one end and overflows (outlet) the other end, No recycle?
need bottom pretty wide open and spillin
what happens sometimes is the inflow from the hose goes along the bottom of the trough, hits the bottom closed part (even if water is spilling over) and some of the water then returns on the surface flowing back toward hose.
Regardless you need to make sure there is no back flow and the dye you add clearly shows a back flow.
I see return flow
I see return flow in both videos. It is visible in the dye and in particles/debris in the water.
low head dams
His demo reminds me of the dynamics at a low head dam. Return flow balances the plunging jet of water and sucks stuff at the surface back toward the dam even though on balance the water eventually spills on down the river.
Harder to avoid than that even
– Last Updated: Mar-12-12 9:39 PM EST –
You are correct but there's even more to this. I mentioned this above but the OP did not pay full attention to my advice. A jet of water crashing into a larger pool will always create eddying back-flow - there is no way to prevent it, and it will happen even if the jet of water does not hit any solid objects (one of my proposed solutions was to place the inlet in a can full of holes so that the water would basically "seep out" around the whole periphery of the can in hundreds of low-speed, low-volume jets aimed in all directions instead of a single high-speed, high-volume jet in a defined direction. I think that would solve this turbulence problem).
As an interesting side note, next time you are on open water and cross the wake of a motorboat within two or three minutes of its passing, note that within the actual path of the prop, the water is slowly streaming backward (relative to the direction the motorboat was going), but for a few feet to each side of that path, the water is streaming forward. Actually, the pair of forward streams are not straight and constant, but a bunch of curly-cues, but the overall impression you will get of the water in those areas is that it is streaming forward. If you get there within about a minute of the boat's passing, this motion is extremely obvious and unmistakable; it's a very large-scale example of what we see in the OP's flow tank.
Eventually!
– Last Updated: Mar-12-12 9:49 PM EST –
Eventually everything go left ->right ; except the . . . . models.
That's the point.
he doesn’t show the far end …
– Last Updated: Mar-12-12 10:08 PM EST –
...... of the water trough but says it's open and not closed .
It's closed or darm near so and the water recirculates , maybe even drains at the head behind or under the hose thing . If it's draing under there that would set up a nice strong reverse flow .
Regardless the drain or not , there is a surface reverse flow that is opposite the feed flow .
Show us the whole trough while you float your brain wood toy . That ain't gonna happen is it ??
What a joke !!
Doubt.
Some of you have valuable observations. These cause me some doubt as well.
The following link is my upload video to show that at the same stream a boat model can move up/down or stay by just changing the attack angle.
- It the repeats of the first minute; I do many times over to see if I can fool with the locations . . . .
http://www.youtube.com/watch?v=bBsYSCI001w&feature=youtube_gdata
Note:
(1) At that slow speed I need to adjust the attack angle . . . If there places seem that I kick then they are not intentional and please disregard them.
Phi.
This is like watching a train wreck.
And the lead-up to another, and another…
An answer
To give an answer to notion of flow back, eddy etc. . .
- The system is caused by the primary force which is the flow of water from the water hose.
- Through this primary energy some are diverted into other form such as turbulence, or. . . eddy?
- These secondary are always less then the primary.
So even there are secondaries the models always flow with the current (when the foil are not setup to harness those energy from the primary.)
And when we setup the right angle to harness, they move forward - against the current
- As shown on my video 3 above.
Phi.
Build a river
Items exist to try it all out fairly easily
-river morphology is being taught to lots of people.
Scale models work at gaining insight
http://www.youtube.com/watch?feature=player_embedded&v=5bqJo5ze3Bk
Foil.
For those who want to play with the concept there are well built foils that you can find at your local junkyard. . . . REAR WING
Using foils to Lift a Kayak from the water might help a little? I believe theire called Fly yaks? as soon as you hit a certain speed the kayak lifts up and flies over the water. The only thing that touches the ground are two foils benieth your boat. Maybe that would be easier to go upstream since there is less friction? (i’m not a physics person) . And of course you would have to paddle like a crazy person 