Sound generated by axisymmetric non-plane entropy waves passing through flow contractions

For a single-component perfect gas, entropy perturbations are associated with the difference between overall density fluctuation and that coming from acoustic perturbation. Entropy can generate sound when accelerated/decelerated by non-uniform flow this is highly relevant to thermoacoustic instabilities for gas turbines rocket engines, noise emission aero-engines. Widely used theories model entropy-generated rely on quasi-1D assumptions which questions of validity were raised recently both numerical experimental studies. In present work, we build upon an analogy theory problem. This was initiated Morfey (J. Sound Vib. 1973) Ffowcs Williams Howe Fluid Mech. 1975) about 50 years ago extended Yang, Guzmán-Iñigo Morgans 2020) study effect non-plane waves at inlet contraction its generation. Comparisons against simulations previous performed validate results.