Active Control of Fan Tones by Means of Wake Filling: Variation of Partial Edge Blowing

Abstract

Trailing Edge Blowing (TEB) injects air into the wake flow of the rotor blades to reduce the pressure and force fluctutations, which are responsible for the excitation of RSI noise. Previous Research has shown that in particular when trying to perfectly fill the Wakes by blowing out air along the full blade span the Approach was surprisingly disadvantageous in Terms of tonal noise reduction. In order to get more insight into the generation of the Sound sources, the present work focuses on the influence of the radial Position of TEB on the RSI tones by partly blocking the series of finve internral blade channels for all blades, causing circumferentially symmetrical blowing patterns with differing radial structures. A large variety of configurations and operating conditions were investigated by means of in-duct microphones as well as with hot-wire measurements in the inter-stage Region of the fan rig. The experimental setup is presented and Chosen acoustic results in the inlet are analysed as a function of different blowing configurations, Parameters, and operating conditions. A theoretical study on two chosed parmater sets of TEB reveals surprising similarities in their acoustics Performance, whereas the radial blowing patterns differ substantially