Feedback Control of Combustion Instabilities Using A Helmholtz Resonator with An Oscillating Volume

摘要

To suppress combustion instabilities, conventional Helmholtz resonators with fixed cavity volumes have been widely used as acoustic dampers in gas turbine engines. However, such dampers are normally only effective over a narrow frequency range and cannot respond to changes in operating conditions. To broaden the resonators effective frequency range, a multiple input single output control strategy (MISO) is developed to actively oscillate its cavity volume to damp combustion instabilities. This is based on the fact that the frequency at which the resonator provides maximum damping can be tuned by altering its geometry. The MISO strategy consists of two algorithms. One is a real-time plane-wave decomposition algorithm. Another is a least-mean-square algorithm with a variable step-size (LMS-VSS), which uses the decomposed wave to determine the optimum actuation signal. The performance of the tuning strategy, carried out with off-line system identification, is evaluated via a numerical model of an unstable combustion system. It is successfully demonstrated that the MISO strategy is capable of stabilizing the combustion system both under varying operating conditions and in the presence of a strong back-ground noise.