Design of actively controlled semi- permeable trailing edge inserts for aeroacoustic noise reduction

Abstract

An experimental study is conducted on the design of actively controlled semi-permeable inserts for mitigating turbulent boundary layer noise originating from the trailing edge of an airfoil. Two sets of perforated inserts with hole diameter: 0.8 mm and hole spacing: 1.5 mm & 3 mm, are considered. The inserts are 3-D printed with a middle-disk shift mechanism to change flow parameters across the perforated disks without modifying the hole diameter and hole spacing. The pressure drop experiments across the inserts are carried out at pipe-level Reynolds numbers ranging from 160 to 2380 to characterize the variation in flow permeability, flow resistivity and formfactor of inserts. The tests are carried out in two phases: static and dynamic configuration. A novel static set-up with orientation pins is devised to implement the middle-disk shift mechanism. For
the dynamic configuration, an actuation device is designed and constructed to control permeability on-line through an external motor controller. The findings show that the middledisk shift mechanism can achieve a maximum permeability variation of DeltaK_max>4.5x10^-9 m2 at a net effective porosity change of epsilon_Eff >72%, for the current set of perforated inserts. The results also suggest that the mechanism is most potent in the range of 50%closed hole (half shut)- to 100% closed hole (completely shut)- orientations. The flow parameter
variations for the static configuration are fairly replicated by the dynamic configuration, thereby, establishing repeatability of the actuation device. Therefore, the dynamic configuration set-up holds good promise for up-scaling to real structures, that is, trailing edge of an airfoil with relevant optimization.