I try not to think in „can this be trusted: Yes/No“ terms but in „Cost/Benefit“ to gain an additional insight at a certain confidence level:
Our goal is to win races. To do so, you have to decide how to spend your time and your money most effectively. Do spend your money on a training camp or a wind tunnel test? Do you do a structured interval session or an aero test? Within testing: Do you run more repeats to increase your confidence or do you test more things?
Quantity and quality VS time and money.
You can turn to statistics and tools/concepts like Bayesian inference and Variance Bias trade offs to help you make these decisions.
The key takeaway out of all of this is that tiny differences are much harder to measure, so the cost to validate them are higher, yet tiny differences are also less valuable, so pursuing tiny differences is bad from cost benefit trade off. Big differences are much easier to make prove AND more valuable, but to find them you have to search broader and in places you haven’t looked/ didn’t want to look.
50% of my work with the US Olympic Committee is working on performance innovation strategy. I dubbed my framework „Pareto Gains“ as a counter movement to marginal gains and is built around exactly this insight.
I built my CFD tool chain accordingly, with the focus to rapidly and cost effectively explore a vast space. CFD also doesn’t require athlete buy in, doesn’t pose injury risk and allows to test positions an athlete can not yet hold, so it allows you to explore broader, reserving the wind tunnel and field testing as validation tools.
Bringing it all the way back to your question: Yes, the bigger the gain, the more confidence you can have in the results, accounting for the specific weaknesses of this CFD approach (more on this in a later post, I feel my posts are already too long). Depending on your performance engineering/innovation budget I would spend roughly 2/3 on exploration-CFD and 1/3 on tunnel testing and do very few tunnel set ups but with 3-5 repeats to push the accuracy of the validation tool as high as possible. If tunnel testing is out of the budget, you can do final validation on the track/ wind-still outdoors. If that isn’t available, making decisions based on CFD alone is better than any alternative which would be guessing, or copying others.