Thanks for opening up the debate. I was getting worried there that I was ostracizing myself by raising the concern.
A2/ Darko (basically the same tunnel design) are certainly an affordable tunnel for trying out ideas. And they both have some really smart guys working for them.
The racing industry in the US has moved towards using Windshear which is significantly more expensive. But does correct a number of the inherent issues with a small closed section fixed ground tunnel. It's not perfect, but it's closer.
I am a little out of touch with F1 these days, but it doesn't surprise me to hear of RedBull's issues. Rules limit full scale testing time, and scale model testing is under increased limitation. Most teams are doubling down on CFD, but mistakes are still made in basic validation between the 3. In an f1 car all it takes is a slight separation point miscalculation and you go from the front of the grid to the back.
CFD is great tool (Woody you can forward the commission check later
) However, without validation to real or tunnel data you might as well be P*&$ing in the wind. The entire premise of CFD is based around solving 2 unknowns. In order to get one unknown (Lift/Drag) you have to make up the answer to the other. This is refereed to as the turbulence model. And which model you choose wildly changes the answer of the Lift/Drag. Not to mention all the other variables, Steady State vs transient etc. It's a real minefield. On a vehicle program (in my day job) I might do 10-15 transient CFD runs before I am happy the model correlates with my tunnel, not many people can afford 15 runs to throw away for validation.
Those who say they prefer to test on the track are not as insane as they sound. With some data logging and some other basic principles a lot of data can be gathered about the aerodynamic performance of the car in the real world.
In short, continue to test and use tunnel facilities and CFD. But don't do so assuming the answers are right. always be critical of what you are looking at.
I am not trying to set myself up here, but if people feel they need help to understand numbers or procedures I'll try to help. I don't have all the answers, but I'll do my best.
I just want racers to be safe. Fundamentally these cars are on the edge of stability, and decisions made in a tunnel or CFD without knowing all the facts could push you over that edge. You don't know what you don't know. And the first key to solving a problem is knowing what you don't know.