Construction and Assessment of an Inflow-Control-Device for a Low-Speed Aeroacoustic Fan Rig

Prerequisite for an undisturbed investigation of fan self-noise generating mechanisms is a fan inflow with negligible spatial and temporal nonhomogeneity. For this purpose, an inflow control device (ICD) was constructed for a low-speed aeroacoustic fan rig operated in laboratory environment. The ICD was built using flexible honeycomb covered on both sides with a thin wire mesh to ensure maximum turbulence reduction. The performance of the ICD was assessed both aerodynamically by means of hot-wire and total pressure rakes, and the fan noise emission was recorded by a microphone array. The ICD established a homogeneous inflow in terms of both turbulence intensity and the mean axial flow velocity. Both the turbulence intensity and the integral length scale profile along the radial direction were fully characterized. Turbulence levels of around 0.1% were achieved in the freestream when the ICD was installed on the inlet. Acoustic measurements revealed more stable rotor-coherent tones, along with a strong reduction of narrowband components around the blade passing frequencies. A reduction of the fan noise broadband levels was also observed.