Abstract
A study of the impact of reverberation on cruise regime acoustic testing of contra-rotating open rotors in a wind tunnel is presented. Models for the rotor tone noise generated in closed cross-section wind tunnels are derived and used in the analysis. The models account for rectangular and circular cross-sections, rigid or impedance boundaries and, for the rectangular wind tunnel case, the rotor axis may be arbitrarily located within the tunnel (but aligned with the flow direction). These models are used to generate simple simulations of model-scale open rotor testing in two real wind tunnels suited to high-speed rotor testing – the Transonic Wind Tunnel in Bedford, UK and the S1MA wind tunnel in Modane, France. In the analysis, the effect of various modelling parameters on the reverberant noise field is investigated. It is shown that open rotor interaction tone noise may be particularly susceptible to the impact of reverberation and that for many tones the reverberant field may persist and contribute to a contaminated noise field, even for wind tunnels with acoustic treatments on the walls of the working section.
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