Random Wind Tunnel and Smoke Pictures Thread

[aerohead]

Originally Posted by kach22i

Quite incredibly the topic this NASA article covers is not accompanied by an appropriate still photo, nor are such images in the poorly edited video.

Your government at work, guess you will have to just use your imagination.

For me this includes a 1980's dance floor with a crystal ball, strobe light and smoke machine.

Sept. 7, 2016
NASA to Shine Lasers on Future Aircraft Concept
https://www.nasa.gov/feature/langley...rcraft-concept

For a couple of decades,Mercedes-Benz has used what they called 'laser doppler anenomometry' to study airflow over their car models.It seems similar.

[aerohead]

Originally Posted by kach22i

Nov. 30, 2012
Common Research Wind Tunnel Model with a Particle Image Velocimetry Plane
https://www.nasa.gov/centers/ames/or...1600-1200.html



I'm just not seeing it.

Perhaps the visualization is too rapid and meant for photo sensors and not the human eye, or at least the eye of a traditional digital camera (or what ever they used here)?

All the streamline filaments passing the model are isoenergetic.They contain the same amount of energy,whether in pressure or velocity,or any combination of the two.
With smoke,any particular filament could be analyzed by measuring the velocity of entrained air molecules as they pass by the model.From Daniel Bernoulli's theorem,they could know the air pressure at any point around the model,based upon the local air velocity vector.
Turbulence,if present,would have it's own velocity/pressure anomaly.
Any three lasers chosen,would act as theodolites,capturing the dynamic vector history of a particle,fixing,through trigonometry,range and location at any given point,much as global positioning satellites can fix the position of your cell phone.

[kach22i]

Originally Posted by freebeard

Amazing Mirror Experiment Reveals Invisible Air Movement!

From the description on Youtube.

This is a demonstration of the Schlieren effect. This setup allows you to see changes in air density. The point light source is aimed at the concave mirror. The concave mirror reflects to a focal point. There you use a sharp edged object to partially block the light which helps create a shadow effect that allows you to see air movement.

The comments section was rather humorous reading, and sort of middle school.

Aerohead,, thank you for the explanation of the NASA posts, but somehow I'm still wondering if there is any visual delight or subjective human brain processing of visuals involved, or if the data is all numbers on a read out.

I'm not getting that therapeutic release of brain emissions which traditional smoke and wind tunnel images give me.

And the "Amazing Mirror Experiment Reveals Invisible Air Movement! " is pretty safe in the "Wow" or "amazement factor" from being challenged by PIV as well.

http://forums.pelicanparts.com/off-t...pics-4008.html


http://forums.pelicanparts.com/off-t...ures-1738.html

[freebeard]

That's a great picture of the Tu-95. A modern wind farm would have the towers staggered, with the blades spinning in alternate direstions, so the vortex street reinforces rather than defeating the downwind units.

What is PIV?

Anyone who finds a large, shallow concave mirror would want a wind tunnel and a razor blade.

[kach22i]

Originally Posted by freebeard

What is PIV?

As previously posted.

https://www.nasa.gov/feature/langley...rcraft-concept

But for this test it looks a little different. The top of it has been painted in non-reflective matte black to accommodate laser lights that will sweep across the model in sheets. NASA and Boeing researchers will use those laser sheets combined with smoke in the technique known as particle imagery velocimetry or PIV. That will map the airflow over the model.

Unrelated:
How do they get away with the related ground pressure interface issues when doing half models on the floor?

Nov. 30, 2012
Ultra High Bypass (UHB) Nacelle Semi Span
https://www.nasa.gov/centers/ames/or...1600-1200.html


Also, by putting the model on it's side wouldn't that upset gravity's effect on air particles?

This configuration has to have an advantage, otherwise they would use the wall as I've seen done elsewhere.

I do see that they can rotate the model to change the angle of attack, maybe that's just where the turntable is?

[aerohead]

Originally Posted by kach22i

From the description on Youtube.



The comments section was rather humorous reading, and sort of middle school.

Aerohead,, thank you for the explanation of the NASA posts, but somehow I'm still wondering if there is any visual delight or subjective human brain processing of visuals involved, or if the data is all numbers on a read out.

I'm not getting that therapeutic release of brain emissions which traditional smoke and wind tunnel images give me.

And the "Amazing Mirror Experiment Reveals Invisible Air Movement! " is pretty safe in the "Wow" or "amazement factor" from being challenged by PIV as well.

MORE random pics...... - Page 4008 - Pelican Parts Technical BBS


Random TRANSPORTATION pictures - Page 1738 - Pelican Parts Technical BBS

My guess is that our retinas will be denied any grist for endorphin release.With the data presented as a spreadsheet,it could be assembled as a colorized image denoting velocity or pressure as a static image.
At flight conditions,a freeze-frame of the action would tell the air heads what they needed to know.
Seems like CFD would already do all this.

[aerohead]

Originally Posted by kach22i

As previously posted.

https://www.nasa.gov/feature/langley...rcraft-concept


Unrelated:
How do they get away with the related ground pressure interface issues when doing half models on the floor?

Nov. 30, 2012
Ultra High Bypass (UHB) Nacelle Semi Span
https://www.nasa.gov/centers/ames/or...1600-1200.html


Also, by putting the model on it's side wouldn't that upset gravity's effect on air particles?

This configuration has to have an advantage, otherwise they would use the wall as I've seen done elsewhere.

I do see that they can rotate the model to change the angle of attack, maybe that's just where the turntable is?

*they're presuming laterally-symmetrical flow with zero yaw.
*the angle-of-attack is the reason for the model position on the turn table.
*any wall-associated boundary layer effect interference can be nullified with suctioning off the boundary layer.
*we'd want to review fluid mechanics,but since all the flow is occurring inside a 'pipe',the gravitational effects to the fluid can be ignored.

[freebeard]

Originally Posted by aerohead

Seems like CFD would already do all this.

This is why I'm intrigued by OpenVDB

OpenVDB

It's open source, being folded into Blender, and you might say it holds a fractal array of voxels (technically a fast shallow and sparsely populated binary tree). It's currently used by, e.g., Dreamworks SKG to make fire, smoke and water in Hollywood movies.

The neat thing is each voxel can have have non-spatial attributes like color, opacity, velocity or pressure. I'm sure what we want could be built on Blenders animation engine.

August 10, 2016

OpenVDB 3.2.0 is now available to download.

Highlights of this release include

tool to produce and store a sequences of progressively lower resolution grids (mipmaps)
an acceleration structure for fast range and nearest-neighbor searches on particles
arbitrary volume and level set specific segmentation tools
a new binary mask grid type and an efficient point to level set conversion scheme
faster volume to mesh conversion and threaded grid destruction
faster morphological dilation, csg operations and fracture tool
New Houdini nodes: Segment, LOD and Topology To Level Set.

See the release notes for more information.

[gumby79]

Sub

[kach22i]

I'm assuming the laminar airflow over the top of the P51 wing would have quite the velocity, in a dive at least.

Notice the tiny turntable built into the wing.

Not sure if this disk would be adjustable in flight, or even how testing data would be accumulate.

Guess I have to read the paper.

http://history.nasa.gov/SP-4302/ch2.3.htm

Wing-flow technique of transonic testing. Models mounted on the wing of a North American P-51.

Reminds me of testing shapes/bodies on the roof of cars.