Coherence analysis of the simulated sound field of a highly-heated laboratory-scale jet

Abstract

Large eddy simulations (LES) have successfully reproduced the flow and acoustic fields generated by laboratory-scale jets. However, laboratory-scale test conditions ordinarily do not match those of full-scale military aircraft. Recently, Liu et al. (AIAA 2016–2125) showed that accounting for a variable ratio of specific heats leads to increased accuracy in LES simulations of heated jets. As a step towards modeling operating parameters similar to military aircraft, they produced a simulation of a highly-heated jet with a temperature ratio of seven. This paper shows the levels in the field as well as the axial and azimuthal coherence trends of this simulated jet. Large axial coherence lengths are found in the direction of maximum radiation with decreased coherence towards the sideline. Azimuthally, coherence length scales are greatest in the region of maximum radiation and generally decrease with increasing frequency. Additionally, evidence is seen for multiple self-coherent and mutually-incoherent radiation lobes within the region of maximum radiation. [Work supported by USAFRL through ORISE.]