Porpoising, flexibile aerodynamics, rotating wheels in CFD?

[Fluido]

Can we include in CFD calculation, spring/damper function, material felxibility, tire rotation/tire deformation(sideslip), so result will predict porpoising, aero materail deformation , tire deformation etc or CFD can only look at car as static object?

[Greg Locock]

On a similar topic we model the car in CFD at a variety of static setups and build up a matrix of the forces generated as a function of attitude. These can then be used in the vehicle dynamics model. Co simulating CFD and vehicle dynamics would be possible but is an excellent way of using CPU cycles up for no real gain.

[n_anirudh]

One could setup an unsteady sim with moving mesh and look at the vortical structures that change/evolve as the car pitches/rolls etc - but these are highly expensive simulations - maybe tens to 100 x the times for a RANS. They would use DDES or hybrid methods for these.

One may (very cautiously!) perform RANS at the extremities/few intermediate points along any characteristic to obtain performance curves.

[Zynerji]

One could setup an unsteady sim with moving mesh and look at the vortical structures that change/evolve as the car pitches/rolls etc - but these are highly expensive simulations - maybe tens to 100 x the times for a RANS. They would use DDES or hybrid methods for these.

One may (very cautiously!) perform RANS at the extremities/few intermediate points along any characteristic to obtain performance curves.

So, even the most advanced usable methods are still using tricks to do these calculations? That almost seems unreasonable at a F1 level with modern hardware partners.

I get it though. Mapping air as it moves isn't easy.

[G-raph]

The technology for this absolutely exists in theory. You need to couple a CFD solver with a FEA solver (which is called FSI : Fluid Structure Interaction) and run a transient simulation with movable mesh (either using a mesh morpher or a geometry morpher and remesh at each time step).

It would be incredibly expensive (way more than 100 times a standard RANS simulation), as already mentioned, especially if you are looking at an entire F1 car.

But the real show stopper is that each tiny modification of the mesh (= each time step) would count as a new run, and as you know these are now restricted by the FIA (in both CFD and Wind Tunnel). I don't think F1 teams would like to spend an entire monthly CFD development allocation to run such a complex simulation.

And the results would probably be wrong anyway.

[Fluido]

.

And the results would probably be wrong anyway.

How are the results even accurate if we treat the car as a static object?

[SharkY]

How are the results even accurate if we treat the car as a static object?

If you look at a car at a very discreet period of time, say 0.05s, the car seems almost stationary, so that's a good approximation. You can than measure the forces, the air is acting upon the car, do this over and over again in different scenarios (geometries) and create a database of forces in relation to the geometry. You can also use a bit more resources to get some simplified (e.g. rear wing only, as you can use formerly generated satic data as boundary conditions) aeroelasticity simulations and add it to the database too.
From this, you can build a mathematical model of the car which takes into account the forces acted upon, the responsiveness of the suspension, etc and voila, you can throw that into a simulator or use it to determine some critical phases, that need further analysis.

The problem with complex transient simulations is that they require extreme computing power and you can never be sure if the results are true as small errors can build up and throw off the flow. So why bother, when you can simplify it to get the close enough results and get the corrections from the wind tunnel and track data?

[Zynerji]

The technology for this absolutely exists in theory. You need to couple a CFD solver with a FEA solver (which is called FSI : Fluid Structure Interaction) and run a transient simulation with movable mesh (either using a mesh morpher or a geometry morpher and remesh at each time step).

It would be incredibly expensive (way more than 100 times a standard RANS simulation), as already mentioned, especially if you are looking at an entire F1 car.

But the real show stopper is that each tiny modification of the mesh (= each time step) would count as a new run, and as you know these are now restricted by the FIA (in both CFD and Wind Tunnel). I don't think F1 teams would like to spend an entire monthly CFD development allocation to run such a complex simulation.

And the results would probably be wrong anyway.

Are there any softwares using point cloud data instead of meshing for this process? I thought the Euclideon Geometry breakthrough from 2005 had already unlocked that tech...

[G-raph]

The problem with complex transient simulations is that they require extreme computing power and you can never be sure if the results are true as small errors can build up and throw off the flow. So why bother, when you can simplify it to get the close enough results and get the corrections from the wind tunnel and track data?

I agree with this.

You have to remember that porpoising is triggered by an areodynamic instability, causing a large downforce fluctuation. If the car was infinitely stiff you wouldn't see it, but obviously it is still sprung so the car bounces.

So all you need to do is find a way to model that aerodynamic instability. Which is why the best approach is simply to run a static geometry with a transient CFD solver (such as DDES). That would be just as good (or even better, as mentioned above) that the fully CFD-FEA coupled setup.

Having said that, if CFD was good enough to capture this phenomenon by simply running a DDES simulation, all the teams would have fixed the issue after winter testing 2022. Which obviously they didn't.

Are there any softwares using point cloud data instead of meshing for this process? I thought the Euclideon Geometry breakthrough from 2005 had already unlocked that tech...

Yes. This is exactly what I refer as "morpher" in my original post. They are quite common and work very well.
You can use this morpher to modify either the CFD mesh directly (using cloud point data to move the nodes and cells), or modify the input geometry (usually stl format or equivalent) in the same way and then re-generate the CFD mesh.

[BritishPowerboats]

Your'e over complicating it. The maths for porpoising has been well understood since 1964. You need to look at engineering principles. For example, consider a wind instruments reed which all have a very shallow angle of attack. they all build pressure then collapse. Ground effect negative pressure is the opposite, but the principle is the same. Merc have an issue with the center of pressure moving rapidly fore and aft as it rapidly reestablishes and collapses.