vorticism wrote: ↑
Tue Mar 08, 2022 6:16 pm
Doesn't matter if it's pilot induced (though it sometimes isn't). Point was: ground effect + undampened spring force creates a feedback loop known as porpoising. Alternating pressure gradients beneath aero surfaces. Both vehicle types have at least one way of curing it: slowing down.
Porpoising on landing isn’t from this.
A PhD aerodynamicist friend said from the first day of testing to me that a possible cause was vortex shedding inducing oscillations that resonate at the same frequency as the suspension. He had experience with this in aircraft and the tools they had at their disposal were greater than the entire F1 grid combined. You can find my old posts from the first day of testing repeating this.
It could be a combination of things, but it was funny to read Jean-Claude Migeot mention this in an op-ed recently about this being a potential cause and how hard that is to fix.
Migeot explained that the cause of porpoising was not in a cyclical stall function, but down to the aerodynamic forces within the underbody at high speed inducing movement in the car close to its natural heave frequency.
This won’t show up in the wind tunnel because those are often rigid models and a scale suspension won’t oscillate the same and Cfd isn’t good enough (plus you would have to run a chassis / tire model at the same time, good luck). Complex shapes with turbulence requires a ton of computing power and nearly impossible to model accurately.
This vortex shedding is actually what causes skyscrapers to resonate and why they have tuned mass dampers.
Von Karmann Vortex’s are a bitch and it’s arrogant to think F1 cars are insensitive to flutter and structural mode interactions.