Novel Approach for Reducing Rotor Tip-Clearance-Induced Noise in Turbofan Engines

Rotor tip-clearance induced noise, in the form of both rotor self-noise and rotor-stator interaction noise, constitutes an important component of total fan noise. Innovative yet cost-effective techniques to suppress rotor-generated noise are, therefore, of foremost importance for improving the noise signature of turbofan engines. To that end, the feasibility of a passive porous treatment strategy to modify positively the tip-clearance flowfield is addressed. Accurate viscous flow calculations of the baseline and the treated rotor flowfields are studied. Detailed comparison between the computed baseline solution and experimental measurements shows excellent agreement. Tip-vortex structure, trajectory, strength, and other relevant aerodynamic quantities are extracted from the computed database. Extensive comparison between the untreated and treated tip-clearance flowfields is performed. The effectiveness of the porous treatment for altering the rotor-tip vortex flowfield, in general, and reducing the intensity of the tip vortex, in particular, is demonstrated. In addition, the simulated flowfield for the treated tip clearly shows that substantial reduction in the intensity of both the shear layer rollup and boundary-layer separation on the wall is achieved.