A Mesh Adaptation Strategy to Predict Pressure Losses in LES of Swirled Flows

The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Program (FP/2007-2013) / ERC Grant Agreement ERC-AdG 319067-INTECOCIS

Dynamics of premixed confined swirling flames.

International audienc

Swirling flame instability analysis based on the flame describing function methodology

International audienceThermoacoustic instabilities are analyzed by making use of a nonlinear representation of flame dynamics based on the describing function. In this framework, the flame response is determined as a function of frequency and amplitude of perturbations impinging on the combustion region. This methodology is applied to confined swirling flames in a laboratory scale setup (2.5 to 4 kW) comprising an upstream manifold, an injection unit equipped with a swirler (swirl number = 0.55) and a cylindrical flame tube. The flame describing function is experimentally determined and is combined with an acoustic transfer matrix representation of the system to provide growth rates and oscillation frequencies as a function of perturbation amplitude. These data can be used to determine regions of instability, frequency shifts with respect to the acoustic eigenfrequencies and they also yield amplitude levels when self-sustained oscillations of the system have reached a limit cycle. This equilibrium is obtained when the amplitude dependent growth rate equals the damping rate in the system. This requires an independent determination of this last quantity which is here based on measurements of the resonance response curve. Results obtained are compared with observations from systematic experiments carried out by varying the test combustor geometry. The demonstration of the FDF framework in a generic configuration indicates that this can be used in more general situations of technological interest

Uncertainties for Thermoacoustics: A First Analysis

International audienceAn Uncertainty Quantification analysis of a swirled stabilized combustor experiment is performed. Theobjective is to estimate the modal risk factor of the system, i.e. the probability of a thermoacoustic mode tobe unstable, which may facilitate the development and optimization of suitable control methods. Topropagate uncertainties, a Monte Carlo method is initially used based on 4000 Helmholtz-basedthermoacoustic simulations with random perturbations on the flame input parameters. The analysis of theMonte Carlo database suggests that a reduced two-step Uncertainty Quantification strategy may beefficient to deal with thermoacoustic systems. First, three bilinear surrogate models are tuned from amoderate number of Helmholtz solutions (a few tens). Then, these algebraic models are used to perform aMonte Carlo analysis at reduced cost and approximate the risk factor of the mode. Good agreements areobtained when comparing the risk factor from the full Monte Carlo database and the risk factor fromsurrogate models