Brilliant way to visualise/see air/fluid flow

[Logic]

This is a brilliant way to see the flow around a body of any shape.
Just brilliant!! And a fellow South African judging by the accent.

https://www.youtube.com/watch?v=CncGLXxG3ZE

[freebeard]

Agreed. No response to my thread from yesterday yet.

ecomodder.com/forum/showthread.php/rheoscopic-fluid

[j-c-c]

Did not see your post yesterday, but yes this is certainly very visual.
Now can I see a "teardrop" trailer test?

[freebeard]

All one needs is a test trailer and a custom receiver hitch. Scientific equipment uses a ring that deforms with a sensor to accurately measure when it goes out of round. So the [removable] hitch would have a ball on one end and a Class 1 or 2 tongue on the other. As the [thick steel] ring in the center goes out of round it's width narrows.

[Logic]

Originally Posted by j-c-c

Did not see your post yesterday, but yes this is certainly very visual.
Now can I see a "teardrop" trailer test?

Ask Him...

Or get some graphite etc.

[j-c-c]

Originally Posted by freebeard

All one needs is a test trailer and a custom receiver hitch. Scientific equipment uses a ring that deforms with a sensor to accurately measure when it goes out of round. So the [removable] hitch would have a ball on one end and a Class 1 or 2 tongue on the other. As the [thick steel] ring in the center goes out of round it's width narrows.

That is a measurement. The previous test shared here gave visual results, staying with that line of thinking, I want to "see" what the "teardrops" actually deliver with this innovative IMO test.

[aerohead]

1) In order for the 'scale' flow to represent 'real flow' ( verisimilitude ) we need a minimum Reynolds number ( Rn ) of around 1,000,000, which is the 'supercritical Rn' for a fully developed turbulent boundary layer to exist.
2) This is essential if 'real flow' effects are desired in a scale model.
3) You'll need the formula for Rn.
4) You'll need the kinematic viscosity of the 'fluid' your choosing for the water table.
5) Knowing the kinematic viscosity, and supercritical Rn requirement, you reverse-engineer the water table flow velocity requirement necessary to balance the equation.
6) If you fail to satisfy all conditions of verisimilitude, what you observe will be 'bogus.' And there's no way you could trust scaling up your results in order to create a 1:1-scale 'body'.
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7) If testing for a 'teardrop' trailer body, 2-D flow will not reveal the extremely high vortex-drag which exists in 3-D flow. This was tested to high precision by Fachsenfeld, who presents the wind tunnel photographs, plus associated drag tables, in his self-published ,1951, Aerodynamiks Des Kraftfahrzeugs.

[freebeard]

1) In order for the 'scale' flow to represent 'real flow' ( verisimilitude ) we need a minimum Reynolds number ( Rn ) of around 1,000,000, which is the 'supercritical Rn' for a fully developed turbulent boundary layer to exist.

I'm having trouble sorting out whether the viscosity of the fluid needs to be greater or less at smaller scales.

Gnats feel air like we do water, so maybe a less viscous fluid like ethanol?

Here's a CFD analysis of fifth-wheel teardrops: www.sciencedirect.com: Shape optimisation of teardrop trailers to minimise aerodynamic drag in articulated lorries

[aerohead]

Originally Posted by freebeard

I'm having trouble sorting out whether the viscosity of the fluid needs to be greater or less at smaller scales.

Gnats feel air like we do water, so maybe a less viscous fluid like ethanol?

Here's a CFD analysis of fifth-wheel teardrops: www.sciencedirect.com: Shape optimisation of teardrop trailers to minimise aerodynamic drag in articulated lorries

1) It all come down to Reynolds number, which must always be 'supercritical.' ( one-million or above ).
2) 'Kinematic viscosity' is part of the equation used to calculate Rn. It must be known, just as with air density ( rho ) in the drag force calculation.
3) 'Scale' is the other consideration, since 'Length' of the body under consideration is literally one of the factors used in the equation used to calculate Rn .
4) 'Velocity' is the limiting factor in scale testing, as there will be a point where flow is so great that air becomes 'compressible' and supersonic shockwave drag can be present around the body, due to it's super-velocity effects.
5) We must limit ourselves to 'low-speed' aerodynamics, of 'subsonic' flow.

[freebeard]

Now that I've thought about it: upside down, *in water*, with hydrogen bubbles.