That’s a question that I receive very frequently, and that’s my usual answer:
The result you get are accurate according to your input parameters if you observe the convergence of the solution.
BUT don’t forget your output results will always depend on your model and your input parameters.
If the input is wrong, you cannot get accurate results. That’s what some people are calling: garbage in / garbage out.
What most people are doing is that they are calibrating the simulation results with real experimental results. If you get simulation results that are matching the experimental results then you know that your approach is correct.
Using only simulation and never compare with reality (experiment/thesis) will rarely provide accurate results… and you will never know if those results are accurate or not…