Modeling Combustion Chamber Acoustics Using the DLR TAU Code

Abstract

Combustion chamber instabilities are poorly understood and remain a major concern during the design phase of rocket thrust chambers. It is therefore desirable to develop numerical tools for investigating combustion stability issues in early phases of thrust chamber design for cryogenic propellants like LOX-LH2 or LOX-LNG. This work was performed in the frame of an ESA TRP “Coupling Mechanisms of Combustion and Acoustics in Rocket Combustors”. In this work, we investigate the ability of the DLR TAU code to predict combustion chamber eigenfrequencies and damping rates for different test cases from earlier REST modelling workshops. A large variety of modelling approaches are investigated and compared to experimental data. Different methods for evaluating the combustion chamber frequency and damping from numerical simulations are presented and discussed. In addition to the investigation of eigenmodes in combustion chambers, the acoustic properties of the TAU boundary conditions are tested in detail in a separate test case. Also partially-reflecting boundary conditions are explored for their applicability to combustion chamber simulations. We find a good agreement between the experimental results from the test cases and simulations with TAU for all test cases considered. Regarding the acoustic properties of the boundary conditions, we present an equivalent acoustic type for all boundary conditions available in TAU.