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Old 11-27-2023, 12:12 PM   #24 (permalink)
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Originally Posted by j-c-c View Post
1. So your racket thread is slightly larger than my current grid solution, .030"
2. My grid openings are projected nearly 4 times larger.
3. Is the downstream "wake" measurement you note observed or measured or calculated? seems very acceptable for my use.
4. The acoustic conservation was what I was trying to reduce by dip epoxying the grid together rather than weave and post tension. Additionally, I thought the epoxy would act as a mass damper, and considered the residue drip while hardening might form a useful drag reducing shape. Bottom line silence is the goal, but not likely achievable. If it's simply an acoustic air resonance caused by simply pass thru a reduced opening, it will be what it is.
5. I appreciate the effort to do an initial test, I/we know more than we did at the start I suspect.
6. I am not clear how Ahemed arrive at his ideal grid sizing.
7. I already addressed the 2d flow influence prior and will just have to live with it.
8. My forebody testing was more to help out with intakes, inlets, winglets, etc which I think this rake/racket might help sort out.

Currently I'm at a standstill waiting on the aero shape tubing for the outer perimeter support.
Suction cups will be the go to mount, and a Hero11.

Thanks again
1) Yes, @ 1mm, the nylon webbing is 0.0393", with a wake of 0.0488, using Sighard Hoerner's schematic representation of the flow.
2) Your enlarged spacing would certainly be a plus.
3) Comparing actual 'known' wake images, to Hoerner's schematic representations, suggests that these line drawings have 100% fidelity, compared to actual flow imaging from which they're derived, and I believe that they can be used with a high degree of confidence.
4) The thing about the epoxy dipping would be the 'thickening' of each strand, which is already an issue, and as the coatings build up, and as they become 'boat-tailed' on their trailing edge, they could introduce a 'flow-straightener' effect, which could 'contaminate' the true orientation of the flow, frustrating your efforts to 'see' what's going on.
5) Yeah, information is what it is, and hopefully helps informs our next move.
6) I'm not even sure if Ahmed used a 'grid' at all. A bridge fiducial can be placed at a distance besides a wind tunnel test vehicle, with the 'tip' of a tuft wand placed successively within an imaginary grid, and photographically captured under a strobe light in a completely-dark wind tunnel, with an open shutter; and without advancing the film at all, 350-plus exposures can be captured on the same frame of film, building up a composite image from these stacked exposures. We did this in the physics lab for acceleration tests when I was at Texas Tech.
7) We do what we can.
8) Give it a go. We'll all learn something. I think it was Colin Chapman, of Lotus, who would strap himself to the top of a car, and while a test driver drove him around on a closed-course, would observe the behavior of tufts on some new prototype.
9) If the suction cups were to fail, some sort of safety lanyard backup would prevent the loss of your test rig.
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Last edited by aerohead; 11-27-2023 at 12:14 PM.. Reason: typo
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