LES Large Eddy Simulation

The interaction between rotor wake turbulence and stators is a major source of fan broadband noise. This paper presents a method on how to obtain the low to medium frequencies using a hybrid RANS/LES method. Three stator vanes are discretized and the mean rotor wake is specified at the inlet. Synthetic fluctuations are also added to the inlet profile to trigger the flow into turbulent mode. Chorochronic periodic boundary conditions combined with temporally damped buffer zones (chorochronic buffer zones) are used to make sure that the deterministic part of the wake interaction is taken care of properly. The combination of chorochronic periodicity and buffer zones in the area close to the pitch-wise boundaries efficiently filters the flow field from turbulence generated stochastic fluctuations. The center blade in the domain is relatively unaffected by the filtering effect and the unsteady pressure field, deterministic and turbulence generated, can be used as a source for both tone and broadband noise. The paper also include a comparison between the proposed method and a simulation with modified blade count and standard periodic boundaries. The tone noise will change when the number of blades is modified but the aim is to see whether this has a significant effect on broadband noise