Inferring propeller inflow and radiation from near-field response, part 2:Empirical application

Data analysis techniques mere previously developed for rotating machinery t hat predicted the far-field radiation, inferred inflow characteristics, and defined the near-field/far-field acoustic Green's function based on measur ements of the pressure near field (Minniti, R, J,, Blake, W, K., and Muelle r, T. J,, "Inferring Propeller Inflow and Radiation from Near-Field Respons e, Part 1: Analytic Development," AIAA Journal, Vol. 39, No. 6, 2000, pp. 1 030-1036). The techniques are applied to a free-running propeller in subson ic Bow. As a first case, the propeller ingesting large-scale, mean-flow dis tortions as mould be present downstream of stators or inlet guide vanes was considered. This simplified case allowed qualitative analysis in the time domain and complimenting quantitative analysis in the frequency domain. In addition, the case acted as a calibrating configuration to map the frequenc y response of the individual blades to the incoming Bow by varying the numb er of distortions present and the rotational speed of the propeller, Based on the results of the first case, the analysis was extended to the propelle r ingesting grid-generated turbulence, Because of the complex nature of the flow, all analysis was completed in the frequency domain. By the use of th e techniques in "Inferring Propeller Inflow and Radiation from Near-Field R esponse, Part 1: Analytic Development," an estimate of the blade summation gain was used to complete the direct solution of the aeroacoustic problem a nd predict the acoustic far field from a measurement of the ingested Bow Ad ditionally, the inflow character was inferred from the near-field measureme nts.