Possibilities and Restrictions on the Use of the Zonal RANS-IDDES Approach to Calculate Fan Noise

The possibility of applying the method developed by the author’s zonal RANS-IDDES method, which includes a scheme with the local introduction of implicitness to the problem of calculating the fan noise of turbofan engines is analyzed. Estimates are presented of the required mesh power to use the wall-modeled LES on 1/4 of the chord of the rotor blades near their rear edges, amounting to more than 600M cells. It is concluded that it is not possible to consider the flow in a vortex-resolving formulation for the boundary layers on the rotor blades from their front edges for the current and promising calculations. The calculation confirms the published ideas that the zonal RAN-S‑LES approach to the vortex resolved with the explicit and high-quality generation of the turbulent content is preferable for such tasks. The importance of the qualitative description within the URANS regions near the front edges of the rotor blades, especially near the radial gap, is noted. A modification of a VSTG generator is proposed, which improves the size of the generation for the nonuniform mean velocity field. As a result, the noise of the fan stage that is consistent with the experiment both in the tonal and broadband parts is obtained.