A study in the near pressure field of co-axial subsonic jets

An experimental investigation of the near pressure field of unbounded subsonic jets has been performed. The near-field pressure was sampled, using linear and azimuthal arrays, on conical surfaces surrounding free jets generated by (1) a single axisymmetric nozzle, (2) a co-axial short-cowl nozzle, and (3) a co-axial short-cowl nozzle with serrations (the co-axial experiments were performed as part of the EU program, CoJeN (AST3-CT-2003-502790), where velocity and temperature-ratios were varied). The objective of the study is to better understand differences in the structure of the flows in terms of their sound production mechanisms. A model representation of the source mechanism associated with coherentstructures in the flow is considered, using both the pressure fluctuations themselves and the pressure-derivative source term from Curle’s acoustic analogy. A filtering operation is then applied in order to identify the structure of the radiating source field.

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