Modeling of a coaxial liquid oxygen/gaseous hydrogen injection element under high-frequency acoustic disturbances

An experimental combustor, designated BKH, is operated at DLR Lampoldshausen to investigate high-frequency combustion instability phenomena. The combustor operates with liquid oxygen (LOx) and gaseous or liquid hydrogen propellants at supercritical conditions analogous to real rocket engines. An externally imposed acoustic disturbance interacts with a series of 5 coaxial injection elements in the center of the chamber. A combination of experimental analysis and numerical modeling is used to provide further insight and understanding of the BKH experiments. Optical data from the BKH experiments are analyzed to extract the response of the flame at the excitation frequency. A new method for reconstructing the acoustic field inside the chamber from dynamic pressure sensor data is used to describe the evolution of the acoustic mode and the local disturbance in the flame zone. An Unsteady Reynolds-Averaged Navier–Stokes (URANS) model of a single BKH injection element subjected to representative transverse acoustic velocity excitation has been computed using a specialized release of the DLR TAU code. The single-element model reproduces the retraction of the dense LOx core during transverse velocity excitation as observed experimentally. The model also provides further insight into the flattening and flapping of the flame. The flapping is identified as the oxygen core being transported by the transverse acoustic velocity.