Density measurements of a compressible jet flow interacting with a tangential flat plate using background-oriented schlieren

Many current and future aircraft designs deal with the problem of jet noise prediction methods when the flow interacts with part of the airplane structure. Data regarding how a planar surface interacts with a jet are limited. To this purpose, an experimental study has been conducted in the Roma TRE semi-anechoic chamber of the Aeroacoustics Laboratory using a Background Oriented Schlieren (BOS) technique. The technique was applied to a compressible circular jet flow interacting with a flat-plate positioned parallel to the axial direction. The aim of the work is to investigate how the planar surface interacts with the high-speed jet flow and influences the shock cell structures, for this reason the BOS set up has been configured specifically to meet the optical constrains related to the jet-surface geometry. Measurements have been performed at different Mach numbers in high subsonic, sonic and slightly under-expanded conditions and considering three relative positions of the plate with respect to the jet axis. The density gradient field is evaluated using a cross-correlation algorithm. The acquired images have been post-processed to obtain the density field by numerical integration of the Poisson equation and analysed together with the wall pressure signals. To improve the solution a patching technique procedure has been developed.