kilcoo316 wrote:Nor in a situation where boundary seperation from the wing/diffuser is a distinct possibility.
There is no such thing as a free lunch when it comes to aerodynamics - what you gain on the swings, you lose on the roundabouts.
Of course you are right. A
panel method can't predict viscous effects, unless using a coupled boundary layer method which assumes full attached flow.
However, the likely hood that a RANS CFD field solver (such as Fluent, CFX, STAR-CD) can accurately predict separation from smooth surfaces (not sharp corners) on airfoils/diffusers within a full car simulation is low. In order to get close we'd have to use an extremely fine mesh normal to walls, coupled with a non-wall function based turbulence model. Such a mesh (of optimally placed cells) for a full car will likely approach over 10,000,000 cells which in Fluent will require upwards of 10GB RAM (most likely run in parallel). Also to really nail airfoil flows at such relatively low speeds (compared to aircraft) we'll need to model laminar to turbulent boundary layer transition, another notoriously difficult task.
Next up in our simulation toolbox is the wind tunnel, which has no trouble simulating full cars and boundary layer transitions. However, using a scale model means the
Reynolds number won't match that of the full size car. Without matching the Reynolds number there is uncertainty as to whether the laminar/turbulent regions on the model will be equivalent to those on the full size car, which relates directly to downforce and drag predictions. Also wind tunnels have issues with blockage effects and stationary/rolling roads.
My point (and I think your point is too) is that no single form of simulation is perfect - each has strengths and weaknesses. F1 teams know this (the best ones do anyway) and use a variety of techniques from hand calculations, through panel methods to RANS CFD and wind tunnels. If we know our objectives (e.g. better understanding, comparison with other designs, optimization), then we are in a good position to select the most appropriate technique, in terms of turnaround time, accuracy and cost.
As you say there are no
free lunches, but there are cheap and expensive lunches, knowing which to choose and when, is what separates engineers from apprentices.
