Experimental analysis of an under-expanded jet interacting with a tangential flat plate: Flow visualizations and wall pressure statistics

A statistical characterization of the pressure load induced on a rigid surface by a high speed compressible jet is carried out experimentally on a simple configuration consisting of a single stream round jet flowing over a tangential flat plate. In order to reproduce the typical cruise configuration of modern long-range aircraft engines, a parametric study is performed in terms of Mach number covering under-expanded conditions from low to moderate amplitudes of the nozzle pressure ratio (NPR). The parametric investigation includes the plate-jet axis separation as well as the axial distance from the jet exit. The background oriented schlieren (BOS) technique is used for a qualitative visualization of the flow features whereas wall pressure fluctuations are measured using flush-mounted Kulite transducers covering a range of axial distances along the flat plate up to 14 diameters downstream of the jet orifice. The wall pressure statistical analysis, carried out both in the physical and the Fourier domain, highlights the trace at the wall of the screech tones and the broadband shock associated noise (BBSAN) as well as the co-existence of downstream and upstream propagating waves in the region close to the jet exit.