Aeroacoustic characterization, noise reduction, and dimensional scaling effects of high subsonic jets

A comprehensive far-field acoustics database was generated for high subsoni c, turbulent jets along with mean total pressure and temperature surveys in the flowfield. The effects of core jet temperature and of external coflow on the far-field noise and mean flowfield characteristics are investigated. The results show peak jet noise generation in aft angles (110 < theta < 15 0 deg). The mean velocity measurements indicate an average potential core l ength in the range of 3-8 jet diameters D-j, depending on the core jet flow temperatures and speed of external tunnel coflow, after which self-similar velocity decay is evidenced. Mixing devices (tabs) were used to enhance ne ar-field jet mixing and were explored as a means for far-field noise reduct ion. These devices decreased the peak jet noise but were accompanied by inc reases in high-frequency noise. The effect of scaling from model-scale to e ngine-scale conditions shifts spectral peaks to lower frequencies, thereby driving high-frequency mixing noise increases (due to tab-generated flows) into the peak annoyance range.