Experimental Determination of Flame Transfer Function Using Random Velocity Perturbations

This study focus on the experimental determination of the Flame Transfer Function (FTF) which can be used to analyze acoustic induced combustion instabilities. In the present work random non-harmonic velocity signals are generated to perturb the flame. This method enables to rapidly determine the FTF compared to other techniques and improves the frequency resolution. A System Identification (SI) technique is applied to model the frequency response of different components of the test bench. It is firstly used to impose a white noise velocity signal at the burner exit, with a tunable perturbation level. SI tools and spectral analysis are used to reconstruct the FTF of a laminar conical flame. Experiments are conducted for different operating conditions and forcing levels. Results are compared with those obtained by harmonic modulations of the flow. They closely match over a large frequency range for small perturbation levels. The limits of the technique are examined when the modulation amplitude is increased.