Dedicated numerical simulations of vortex-nozzle interaction indirect noise in solid rocket motors (SRMs) are presented. It is assumed that the flow in the nozzle and hence the sound radiation is not significantly influenced by the global acoustic oscillation of a SRM. Therefore, the study is limited to the acoustic response of a semi-infinite pipe terminated by a choked nozzle. The nozzle considered here is placed flush in a wall forming a right angle to the walls of the combustion chamber. The study focuses on where sound is produced due to vortex-nozzle interaction. The presented results indicate that sound is produced when the vortex is on its approach to the nozzle, rather than by impingement of the vortex on the nozzle walls.

In solid rocket motors, vortex nozzle interactions can be a source of large-amplitude pressure pulsations. Using a two-dimensional frictionless flow model, a scaling law is deduced, which describes the magnitude of a pressure pulsation as being proportional to the product of the dynamic pressure of the upstream main flow and of vortex circulation. The scaling law was found to be valid for both an integrated nozzle with surrounding cavity and a nozzle geometry without surrounding cavity that forms a right angle with the combustion chamber side wall. Deviations from the scaling law only occur when unrealistically strong circulations are considered.