Experiments to mitigate flow recirculation in a closed anechoic chamber using mesh screens as turbulence suppressors

The desire to gather acoustic data of a propeller in simulated hover without environmental effects is met with the challenge of recirculating flow in a closed anechoic chamber. Flow recirculation in an anechoic chamber is not ideal because the effects of it being ingested by the rotor cause unsteady loadings on the propeller. This unsteady loading causes vortex noise from the turbulence introduced by the recirculation of the flow. The aim is to study the acoustic signature of a propeller separate from external factors and engine noise. Two different propellers with three different screen combinations were tested in a closed anechoic chamber. The results of these tests showed that the screens are able to reduce the vortex and broadband noise levels, with the reduction being more pronounced when the dual screen was installed