Thank you for your response. To achieve a value of f<5, I will need to further refine my mesh significantly. I also have a question regarding the mesh quality near the walls. As I mentioned earlier, my goal is to use LES results to extract pressure fluctuations on the walls of the duct for harmonic acoustic analysis. However, based on my RANS results, I have noticed that the mesh resolution near the wall for LES is not fine enough (f<5) in this case. Since it is crucial to accurately capture the pressure fluctuations near the wall, I would appreciate your suggestions on how to refine the mesh in those areas. Would it be recommended to use prism layers in simulations of this nature?