Inferring propeller inflow and radiation from near-field response, part 1:Analytic development

In general, the physics of the relationship between the pressure field surr ounding a rotating propeller in subsonic flow and the how characteristics i s understood. However, quantification of this relationship in a way that al lows engineering analysis of propeller noise is limited by complete definit ion of the inflow distortions. Therefore, a way of inferring this relations hip and the distortion characteristics unobtrusively and in situ has been d eveloped. The technique is based on the assumption that measurements of the unsteady pressure on the blades are available. From the pressures, the tec hnique predicts the radiated acoustic far field, infers incoming flow chara cteristics, and defines Green's function between the near and far pressure fields. The analysis combines theoretical and empirical treatments of press ure data to infer the acoustic quantities. Thus, the turbulence ingestion p roblem is approached in a practical manner without the need for many of the simplifying assumptions required by purely theoretical means. The techniqu e is developed for, use on experimental data, The technique is subsequently applied to a propeller operating downstream of large-scale, mean-flow dist ortions, and ingesting broadband turbulence (Minniti, R. J., Blake, W. K., and Mueller, T. J,, "Inferring Propeller Inflow:and Radiation from Near-Fie ld Response, Part 2: Empirical Application," AIAA Journal, Vol. 39, No. 6, 2001, pp. 1037-1046).