The Effects of Temperature on Vortex-pairing Noise in Axisymmetric Subsonic Jets

Thermal effects on the sound generation by vortex pairing are investigated in axisymmetric subsonic jets. Direct numerical simu- lation of compressible Navier-Stokes equations is performed for an accurate description of near-field flow dynamics and far-field sound. As the core temperature increasing, the positions of vortex roll-up and pairing move upstream, and the noise intensity is enhanced. In addition, sound predicted by Lilley-Goldstein acoustic analogy is consistent with the result of simulation in all cases. A further analysis of sound sources of the Lilley-Goldstein equation shows that the thermodynamic component has remarkable influence in non-isothermal jets, especially in the cold one. Moreover, sound generation in the isothermal jet is specifically studied by a simple nonlinear interaction model based on instability waves which are obtained by solving linear parabolized stability equa- tions. The major radiation pattern given by the model is found to be in good agreement with the directly computed data, suggesting the great importance of nonlinear interaction in subsonic jet noise.