Numerical Study on the Effects of Re on the Unsteady Behaviors in a Transonic Axial-Fan Under Inlet Distortion

The dynamic response of a compression system is the complex dynamic behaviors reacted by the compressor subject to non-uniform inflow excitation. However, in a real operating condition, the compressor would work at a wide range of altitudes within the flight envelope, which forces us to consider how Re additionally affects the compressor performance loss and dynamic response characteristic due to inlet distortion. To explore this issue, a full-annulus unsteady 3D simulation has been used to calculate the performance of a transonic axial fan with a 180-deg distortion at different Re. The results show that Re has additional detrimental effects on the fan aerodynamic performance with non-uniform inflow. To further explore the mechanisms of Re effects on fan–distortion interaction, the spatial and temporal distribution of the rotor blade response is discussed. The temporal distribution of the fan–distortion interaction is not changed with Re by analyzing the dynamic response orbit of the fan rotor. However, the spatial distribution of Re effects is highly related to the blade profile loaded mode at different spanwise locations. The results indicate that the time constant of fan dynamic response decreases by 17% at the mid-loaded region in the middle of the blade and increases by 40% at the aft-loaded region near the blade tip. Further analysis reveals that due to the low Re and flow separation of the suction surface, the thickness variation of blade boundary layer is the main cause for varying the blade time constant.