Analytical Study of Wind-Tunnel Acoustic Testing of Propellers

An analytical study based on finite element models is made of the acoustic testing of propellers in a wind-tunnel environment. Features that are considered are the subsonic mean flow, including the effect of a boundary layer; acoustically absorbing wind-tunnel walls; and a lifting line representation of the propeller. The boundary layer is approximated by several layers of uniform mean flow with interlayer boundary conditions forcing continuity of particle displacement. Results are presented as simulated acoustic measurements made at various locations around the propeller in the wind tunnel. Comparisons are made with similar simulated measurements generated by a free-field, finite element model of the same propeller. In the present study, the tunnel Mach number is limited to M = 0.5, only purely resistive wall treatment is used, and relatively thick boundary layers are considered. It is found that acoustic pressures near the propeller and removed from the walls compare well with pressures in a free-field environment.