Hierarchical Turbulence and Geometry Modeling: Case Study for Fan Stage Flows

Flow separations occur in the tip region when the fan is operating at the approach condition. To reduce computational cost without degrading accuracy, the hierarchical modeling approach has been developed to predict such fan flow. This allows both flow and geometry to be treated with various fidelity levels in different zones. To be specific, this is achieved by zonalizing large-eddy simulation (LES) in the fan tip region and modeling downstream stators with low-order blade body forces. This approach provides an accurate and economical prediction of separated fan flows in the stage environment. The predicted fan wake profiles show a reasonably good agreement with the hot-wire measurements considering passage-to-passage variations. Finally, the simulation data are used to assess the isotropic turbulence hypothesis that is made on fan wake in low-order acoustics models.