Far-field acoustic characteristics of supersonic jet from conical, Rao and Double Parabolic Nozzles – an experimental investigation

Purpose This paper aims to compare the far-field acoustic characteristics of the recently designed contoured Double Parabolic Nozzle (DPN) with the conventional contoured Rao nozzle and conical CD nozzle. Design/methodology/approach Each nozzle is designed and fabricated with a design Mach number of 1.6. Two cases of all three nozzles, flanged (lip thickness = diameter of nozzle exit) and unflanged (lip thickness = 0.04 mm), have been analyzed at the design NPR of 4.25, as well as under various overexpanded and underexpanded NPR conditions, at different polar locations ranging from 25 degrees to 105 degrees from the downstream jet axis. Findings The results show that the DPN’s Overall Sound Pressure Level (OASPL) values are 2.22–4.5 dB lower than those of the Rao nozzle and quieter than the conical nozzle by 3.21 to 5.42 dB. In addition, the screech tone of the DPN is lower in over-expanded and under-expanded conditions and is absent at the design NPR, whereas the other two conventional nozzles exhibit screech tones even at the design condition. Research limitations/implications The acoustic data provide sufficient information to characterize the aero- acoustic performance of each nozzle. However, flow visualization techniques like Schlieren or shadowgraph will support the explanation of the shock cell structure and thus the acoustic behavior. Practical implications The design of contoured converging-diverging (CD) nozzles has a significant role in the supersonic and hypersonic regimes. CD nozzles with reduced acoustic signatures are preferred by the aerospace industry. Social implications The findings support the development of quieter, fuel-efficient supersonic jet nozzles, helping to reduce noise pollution and environmental impact in aerospace applications. Originality/value To the best of the authors’ knowledge, this work presents the first in-depth study of how internal nozzle contouring affects far-field supersonic jet noise, offering novel insights for acoustic optimization in supersonic nozzle design.