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Old 07-14-2023, 06:07 PM   #721 (permalink)
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Quote:
Originally Posted by freebeard View Post
Do you know about graysgarage? ecomodder.com/forum/showthread.php/automotive-aerodynamics-video-series-31047.html

He employed an open-top test section and hydrogen bubbles. Upside down.
ive seen a lot of his videos. they are really cool

i dont have a set up like that, so the easiest thing i can do is in water flow. it may not be as detailed, but i can at least show whats happening in the wake for example

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Old 07-14-2023, 08:07 PM   #722 (permalink)
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Some sort of test section that you can immerse in the river, with an upstream difusser and a window against a backdrop so you can see?

edit:
A scond-hand aquarium with the ends knocked out might be a good donor.
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Last edited by freebeard; 07-14-2023 at 11:37 PM..
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Old 07-15-2023, 02:41 PM   #723 (permalink)
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Quote:
Originally Posted by freebeard View Post
Some sort of test section that you can immerse in the river, with an upstream difusser and a window against a backdrop so you can see?

edit:
A scond-hand aquarium with the ends knocked out might be a good donor.
In the stream I would just have to raise or lower the model depending on what cross section I want to see. And then rotating it would let me kind of see what itís doing to the top of its body

Main reason Iím trying to do this is just to see how the rear ďbox cavity finsĒ affect the wake in the rear versus the default OEM shape
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Old 07-15-2023, 04:02 PM   #724 (permalink)
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I applaud your effort. Would you submerge it or use the surface wake to cut a cross section?
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Old 07-15-2023, 07:21 PM   #725 (permalink)
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I applaud your effort. Would you submerge it or use the surface wake to cut a cross section?
Surface wake. I see a lot of it behind rocks and boulders sticking out of the stream, and at the end of my sluice box
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Old 07-17-2023, 10:21 AM   #726 (permalink)
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'water tunnel / water table'

A water table would allow qualitative flow investigations in 2D flow.
For 3D flow you need a water tunnel, since our cars are 'completely-submerged' bodies on the tropospheric ocean floor.
Long ago, Myth-Busters created a sort of water tunnel from a shallow pool with an inside partition, and used a battery-powered trawling motor to circulate the water, in a continuous stream.
Very small Tygon tubing can be arranged within the model, to inject food coloring into the stream for flow imaging. We used this at Texas Tech for both the water table, water tunnel, and underwater tow-tank.
When the water gets murky, a shot of bleach instantly clears it up.
With SCUBA goggles you could observe your model while you inject the 'dye' with a squeeze-bulb.
You'll never be able to 'measure' forces, but you will be able to observe flow at a proper Reynolds number, with just a couple of mile per hour flow velocity.
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Old 07-17-2023, 03:06 PM   #727 (permalink)
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Quote:
Originally Posted by aerohead View Post
A water table would allow qualitative flow investigations in 2D flow.
For 3D flow you need a water tunnel, since our cars are 'completely-submerged' bodies on the tropospheric ocean floor.
Long ago, Myth-Busters created a sort of water tunnel from a shallow pool with an inside partition, and used a battery-powered trawling motor to circulate the water, in a continuous stream.
Very small Tygon tubing can be arranged within the model, to inject food coloring into the stream for flow imaging. We used this at Texas Tech for both the water table, water tunnel, and underwater tow-tank.
When the water gets murky, a shot of bleach instantly clears it up.
With SCUBA goggles you could observe your model while you inject the 'dye' with a squeeze-bulb.
You'll never be able to 'measure' forces, but you will be able to observe flow at a proper Reynolds number, with just a couple of mile per hour flow velocity.
i did a little test with a tesla model y hot wheels model at the river yesterday and then taped on the cavity fins. the wake behind the model with the fins seemed a little '' sharper/cleaner'' and faster, while the OEM shape seemed slower with more turbulance behind the wake. the wake sizes overall looked about the same
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Old 07-17-2023, 04:36 PM   #728 (permalink)
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Hot Wheels is 1/64th scale. aerohead will have an opinion on the Reynolds numbers involved, but in air 1/4-1/5th is minimal. Maybe you could find a 1/10th scale R/C body.
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Old 07-17-2023, 09:09 PM   #729 (permalink)
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Quote:
Originally Posted by freebeard View Post
Hot Wheels is 1/64th scale. aerohead will have an opinion on the Reynolds numbers involved, but in air 1/4-1/5th is minimal. Maybe you could find a 1/10th scale R/C body.
I have a huge block of wax I was going to carve out to a similar shape as my Ionia and then see what diff separation edges versus tapered cavity fins look in the wake
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Old 07-20-2023, 10:38 AM   #730 (permalink)
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'HOT WHEELS'

At Texas Tech their minimum model scale for the water tunnel was 1:24. That was for 'qualitative' work only. No measurements possible.
The underwater tow-tank used 2/3rds-scale models. $ 68,000 for a model, but the 6-axis sting provided meaningful quanta. SCUBA divers would be down there with video equipment to capture flow imaging.
AeroStealth purchased a $40.00, 1:24-scale die-cast Tesla Model X online and shipped it to me. I created a paint-matched boat-tail for it, and shipped it back for his You-Tube channel.
If you could find one of these for the IONIQ, it would end up cheaper and better in the long run. Cheapest $40 you ever spent.
As freebeard said, the HOT WHEELS is Reynolds number challenged.
If you know the rivers flow velocity, there are formulas and tables which would help you determine if you're achieving supercritical RN. If you're not, you're just gonna be peeing in the ocean and expecting to experience sea level rise.

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