Acoustic modification prediction using FRF: application of Helmholtz resonators on a rocket engine combustion chamber

摘要

This paper presents the application of a method that uses acoustic Frequency Response Functions (FRF) to predict modifications in an original acoustic system: in this case, a cavity of a rocket engine combustion chamber. As a cavity modification, the insertion of Helmholtz Resonators (HR) was applied. The use of HR in such chambers attenuates the effect of combustion instability, which can seriously damage the engine. The Acoustic Modification Prediction (AMP) method using FRF is based on the Structural Modification Using Response Functions (SMURF), which is a well-known structural reanalysis technique. The AMP uses the FRF matrix from the original cavity and the analytical model of the HR to predict the behavior of the new cavity, avoiding the use of large models. In order to validate the prediction results, experimental data were used. The first results presented differences in magnitudes, but it was possible to identify the modification behavior, as well as parameters to be enhanced to have a fully validated method.