Upstream Potential Propagation Effects of Unsteady Stator-Rotor Interaction in an Axial Flow Blower: Numerical Analysis and Experimental Validation

The potential effect of the inlet guide vanes blockage is predominant in an axial one-stage configuration when the upstream flow field is considered. In the same way, rotor downstream, the main unsteadiness is provoked by the rotor wakes mixing-out at the machine discharge. Nevertheless, if the gap between the rows is significantly reduced, the stator wakes are not allowed to be mixed out before impinging the rotor blades, so a chopping effect overcomes, stretching and tilting them, and generating wake-wake interactions and new loss sources at the exit. On a similar trend, it is expected that a reduced axial gap allows the potential unsteadiness of the rotor blockage between the blades to be propagated upstream, modulating the flow conditions at the stator passages, and even at vanes leading edge locations. In this paper, the evolution of the rotor potential interaction within the stator passages and up to the vanes leading edge is analyzed. The main goal is placed on the analysis of the propagation, relating the axial distance with the attenuation of those potential mechanisms. A numerical 3D simulation of a complete single stage axial flow blower has been developed and executed using a commercial code that resolves the URANS set of equations. The axial gap between the 13-IGVs stator and the 9-blade rotor has been modified in order to evaluate its influence on the potential distortion propagated upstream of the stator. For the closing of turbulence, a LES scheme with a Smagorinsky-Lilly model is used in the computations. Finally, due to the LES characteristics, a phase-averaged procedure has to be introduced for the simulation post-processing. Complementary, experimental measurements have been carried out over a test rig with modifiable axial gap between the fixed and rotating blade rows. As a matter of fact, pressure transducers were placed all along the machine shroud to capture pressure fluctuations related to potential sources radiated from the rotor blades. These measurements have been analyzed using frequential analysis, which is essential to identify the origin of the flow inlet distortions. The final objective is to complete the rotor-stator interaction scenario both downstream and upstream the stage. Previous works were focused on the downstream conditions and now the upstream potential propagation is studied in detail.