Materials of Wind Tunnel / Scale Model

[ericengines]

Hi lads and lasses, new to this forum,

I have been a passerby of this forum or rather the entire website for quite a while.So, I decided to create an account and converse with like-minded individuals and peers who I think us motorsport/ automotive engineering degree students, would deem extremely valuable. (apologies for the boring prologue)

Right, the main bit, my question or rather seeking confirmation. Is the scale model of the F1 car made out of different materials? Plus would the finished, track-ready car differ in surface roughness compared to the scale model? I am trying to argue that surface roughness is affected between the two, due to differences such as panel gaps, paint finishing, and pre-preg carbon layups, thus affecting Reynolds Number.

This is for an assignment of mine, but can't find anything conclusively saying that the scale model is the same as the real car in composite materials, texture, etc. Plus I don't want to assume because assumptions have to be referenced as you know per rigorous academia.

I would greatly appreciate it if someone could either point me to the right direction or validate it with a source. Unless you are a part of the technical world of F1, then that's the pot of gold I am looking for.

Thanks again and let's all enjoy the 2025 season before the regulations and new cars are introduced.

[Tommy Cookers]

these are 50% models not 5%
roughness-wise the worry is about the ground plane model not the car model

[jjn9128]

Wind tunnel models are made from a variety of materials based on mechanical requirements of the part. Wings will typically be metallic for stiffness, body panels will be a variety of different rapid prototype or 3d printed parts. All painted a homogenous colour, typically chosen to minimise reflections when using PIV for flowfield analysis.

The car is more split up in the wind tunnel to allow modular changes of parts, so a sidepod/engine cover which is maybe 2/3 pieces on the car could be 20/30 panels in the wind tunnel. Panel splits are then taped over (or not) depending on the underlying construction and whether there is a bleed path which would impact aero conclusions for a part.

Not sure there are any academic sources, The honda 3rd era papers by Ogawa might have some info about wind tunnel construction, but they're nearly 20 years out of date now. There's a series of papers by Nakagawa from Toyota (some in Japanese) about their wind tunnel testing, but mostly about flowfield analysis if I recall correctly and again 10 years out of date. There are some videos by Willem Toet on youtube about wind tunnel testing, but I can't remember what details he goes into.

[JordanMugen]

Wind tunnel models are made from a variety of materials based on mechanical requirements of the part. Wings will typically be metallic for stiffness, body panels will be a variety of different rapid prototype or 3d printed parts. All painted a homogenous colour, typically chosen to minimise reflections when using PIV for flowfield analysis.

Do you suppose there is little to no intention to recreate aeroelastic, flexible or porpoising effects in the wind tunnel?

I.e., the wind tunnel model is designed to be "as if" it is infinitely stiff?

[Rigid?] wind tunnel car models or CFD simulation car models consisting of shapes representing the deflected position of front or rear wings/flaps, would certain be something the FIA could be suspicious about with respect to wings being deliberately designed to flex (if teams would do something so overt!).

[Sorry, this is beyond the scope of ericengines' question. ]

I would be surprised if the surface roughness is important (within reason, unless you are talking >10mm roughness), whether it's the equivalent of 3000 grit sandpaper, 1500 grit sandpaper, 200 sand paper or even 10 grit sandpaper.

According to this random pdf I found online (please use a reputable source instead ericengines!), 36 grit is equivalent to 4.06 micron RMS surface roughness, while a "mirror" finish is considered equal to 0.13 micron RMS surface roughness.

The boundary layer very quickly becomes much thicker than even 10 grit sandpaper. As long as you have your no slip condition, does surface roughness matter?

A rough surface could act as lots of little trips or vortex generators to generate hairpin vortices and trip the transition to turbulence earlier on the surface than "normal", but this might even be a desirable thing?

[JordanMugen]

As you imply, poor panel fit lines could/will act as tiny trips. But whether that's important or not is hard to say. Usually the seams are all taped up.

If the boundary layer is already turbulent where the small step in the surface is, then it's unlikely to make all that much difference surely?

Flow visualisation paint would help show if or where misaligned junctions are causing separation bubbles and how big those separation bubbles are. [Edit -- they may be laminar separation bubbles, so the flow downstream of the small step may reattach and still be laminar if it's a favourable pressure gradient and/or still at low flat plate Reynolds number.]

Even things like exposed dome head screws, rather than flush-fitting countersunk screws, only seem to affect a few mm either side in any case -- going by the flow visualisation. [This is on a flat plate though, all bets might be off for exposed screws or bolts on critical locations like corners.]

[Farnborough]

Unsure if this would assist https://arc.aiaa.org/doi/10.2514/6.2022-0149 primarily above F1 scope in speed, but related.