Would this test set-up be informative?

[aerohead]

Originally Posted by j-c-c

It's not something I have seen or read about. It seems wool tuff testing is useful but often seems to be mainly 2d in its results. I'm wondering if a say 1/2" thin wire but rigid multicolored tuff grid (tuffs attached at nodes on the grind), say 24" square, mounted perpendicular to air flow might give a clearer picture of airflow around say a door mounted mirror if placed slightly down wind, or say mounted just in front of the leading edge of the grille intake/hood/bumper area, or any location to gather a clearer picture of air flow, short of a computer..
My concern is, how much the thin wire grid would distort the takeaway.
Worth a try?

Wire has a drag coefficient of Cd 1.17, higher than a sheet of plywood, crossways in the wind. If you did the grid you'd want to use as 'small' a wire as you could find. Like a 0.008 #1 guitar string or piano wire.
Long ago, the bi-planes used 'streamline' wire for all the tension bracing between the two wings, and it was designed for low-drag, with a 'teardrop' cross-section. Wicks, or one of the other catalog stores for experimental aircraft supplies might be a source. Don't know.
A problem with it is that, if the airflow is not 'parallel' to it's symmetrical streamlined chord profile, you'll get separated flow, and the turbulence will affect what the tufts are 'telling' you.
For the mirrors, the 'tennis racket' is a very good idea. If the wire is properly 'stretched', where they cross, will not require bonding, as in wire fabric.
In my wind tunnel, I use hollow aluminum radio-controlled aircraft wing strut from hobby shops to attach my yarn to, and then rotate it in the airstream to see at what angle of attack the flow is actually moving, then I know that I'm getting as good a flow representation as I'm likely to get.
For the front of the car, you could create a 'holder', which is mounted outboard of the body, like is done with 'Go-Pros', and extend the strut 'into' the footprint of the nose from there, taking care to 'aim' it.
In a wind tunnel, you'd just use a propylene glycol smoke generator and wand ( a vey large 'vape' ).
For the back of the car, do as was already mentioned about Lightyear.

[j-c-c]

Not clear what the difference here is in concept between my original idea and the tennis racket that you and I both really like, except the racket has unique real time positioning attributes.

In my test setup my intention was not to weave the solid wire grid, ala a tennis racket, and the epoxy dip glue process intended was to prevent/reduce wire vibrations by connecting the cross wires and maybe improve the cd as the epoxy hardened as it drains off, improving the trailing edge shape, even if
I have to dip/coat it a few times.

Regardless, I'll try a 9? tuff 3d mini square with wire and see how it looks before I proceed. I was also thinking with the diameter of the wire vs that of the cross-sectional size of the tuff, and the length of the tuff, wire induced turbulence would minimally effect the visualization results, but that would be an unknown until tested in my mind.

[freebeard]

Badmiton > tennis > crochet hoop

https://hearthookhome.com › hanging-baskets-free-crochet-pattern
Hanging Baskets: Free Crochet Pattern - Heart Hook Home
Materials: Steel metal hoops (6″, 8″, 10″, 12″, and 14″ hoops pictured) -I purchased mine individually at Hobby Lobby inexpensively ( here ), and you can also find a whole set of these six sizes on Amazon ( here) in gold.

A circular frame can be tensioned, where a square frame will warp into a saddle shape.

[j-c-c]

True, but in this context, that matters how?

[j-c-c]

I wonder if I could use .030 alum welding tig rod and run it thru a bead roller with angled rollers to seek a teardrop approx/improved shape?

That would end the luxury of burning off old tuffs with high heat/flame when time calls for their replacement when not using ss for the grid.

[freebeard]

True, but in this context, that matters how?

High dynamic loads in a public roadway?

Let's compromise -- a triangle, else two diagonals or four corner brackets for the square.

Why are you resistant to reducing the cross section? I suggested 1-2 thou, aerohead 0.008 #1 guitar string or piano wire.

I wonder if I could use .030 alum welding tig rod and run it thru a bead roller with angled rollers to seek a teardrop approx/improved shape?

Good luck with that. They will still need to be in tension and cross each other.

[j-c-c]

Originally Posted by freebeard

High dynamic loads in a public roadway?

Let's compromise -- a triangle, else two diagonals or four corner brackets for the square.

Why are you resistant to reducing the cross section? I suggested 1-2 thou, aerohead 0.008 #1 guitar string or piano wire.



Good luck with that. They will still need to be in tension and cross each other.

I am not concerned that the loads will be high, nor will I be undertaking any testing with nearby traffic, albeit stll on a public road.

No need to compromise, the thin wire is likely the best option, except I am concerned with the amount time/complexity involved in the small wire tensioning (tig rod requires no tension), and the cumulative forces on a rectangle frame from that tensioning already noted, and lastly, is there bang for buck with the small wire solution. One little mentioned aspect so far, any attachment of a wool tuff of a size large enough to be videotaped and analyzed by the naked eye, will likely require an up wind glue glob attachment many times the size of any small wire solution, and the glue being centered axially with the tuff and hard to minimize, will almost in my suspicion completely negate any improvements a small wire solution might provide regarding induced turbulence..

[freebeard]

What sort of inter-tuft spacing and tuft length do you contemplate?

Tie the tuft in a knot and snip off the un-free end.

[j-c-c]

Multi color by row, 1'Sq, assuming a 24"x12" frame, with 1.25" gap on each side to reduce frame interference, grid spacing allows 94% opening per square with .03" wire/rod.

I was also considering adding a spot of glue to the tuff ends to see if that might mass dampen/steady the tuff fluctuations.

Frame is at this point streamline tubing .45"x .27"

[aerohead]

I did a rudimentary 'road test' of my tennis racquet. It's an adult, HEAD, Liquidmetal, Supreme. It's a light metal hoop / strut / handle, strung with 1mm-diameter Nylon. The mesh opening dimensions vary, depending upon position within the inner boundary of the distended hoop.
The 'most dense' pathways are near-center, creating a rectangular opening, 13mm by 10mm.
Due to flow separation, the wake, downstream of the 1mm string is 1.244mm, resulting in a vena-contracta-esque narrowing of the airway to 12.51mm by 9.51mm.
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1) Just 'swinging' the racquet produces an audible acoustic signature.
2) At 35-mph, it begins to 'sing' appreciably.
3) At 60-mph, it's 'roaring' significantly, and my wrist tired rapidly, attempting to steady the racquet in the oncoming airstream.
4) I've no means to parse out, and properly attribute the sound contribution and associated drag between the hoop and string grid.
5) I'm unwilling to invest the time to 'streamline' the hoop, and re-test.
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I suspect that there'd be little trouble coming to a consensus that, the noise was an artifact of separation, and any use 'upstream' of a road vehicle's body , or components would be unacceptable.
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Onset flow to side mirrors is typically 3-dimensional, making alignment of 'ALL' of the grid, normal to the flow downstream of a mirror problematic.
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I revisited Syed R. Ahmed's flow traverse research reported between 1979 and 1984. The 'densest' concentration of tuft intersections, in a half-body- width grid, was for the fastback body, with a Cartesian grid of eleven vertical columns, and thirty-two horizontal columns.
Based on the metrics he used for grid sizing, for a 2018 Nissan Leaf, imaging would require a grid of 73.6-inches height, by 42.3-inches width, with 352-tufts, spaced at around 3.5-inches, by 2.25-inches. Perhaps this would be a reasonable tuft population density.
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'Streamlining' the grid elements would introduce a 2-D flow bias within a 3-D flow environment. One might get some of the grid properly addressed with respect to some of the oncoming flow, while the rest of the flow would be unaligned, introducing transverse contamination of the flow field of interest.
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Tufting the side mirror itself would preserve fidelity of the actual flow.
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Since Hucho et al. published their shape optimization research in 1976, and new car production cycles back then ran about 48-months, it's hard to imagine a new production car manufactured after 1980, which would demonstrate significant flow issues for their forebody.
' Saturation' leading edge radii relationships were known by this time, and by 1969, the world community of auto designers were in possession of shape 'recipes' which would produce Cd 0.245, as of 1969.
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It seems to me that if everything published by 1976 is addressed, then lower drag will just come down to body elongation, along known streamlined contours/ silhouettes, also reported by 1969, if we ignore those known for over a hundred years now.