IDENTIFICATION OF HEAT RELEASE RESPONSE FUNCTIONS AND THEIR APPLICATION TO LOW ORDER MODELS IN A SINGLE ELEMENT COMBUSTOR

The present thesis focuses on the development of a low order model for studying high frequency longitudinal combustion instability. Quasi-1D Euler equations are applied for the investigation of a self-excited single element combustor. The ob- jective is to prove the model capability of reproducing the unstable behavior if a suitable response function, describing the coupling between acoustics and combus- tion, is provided. In the present work the results of multidimensional high fidelity simulations, performed for the same test case, are matched using the low order model. Two formulations of response function are developed and calibrated: pressure and ve- locity time lag. The main parameters of the response functions are estimated on the basis of two different high fidelity simulations. In particular, hybrid RANS-LES and URANS simulations have been used. The contribution of the present work in the former consists in post-processing the data while the latter has been performed as part of the present thesis. The methodology for estimating the characteristic pa- rameters of the response functions is discussed. Finally, a sensitivity analysis is performed on the model main coefficients to assess their effects and the tolerance that can be associated in their estimation. Moreover, the analysis has the objective to test the formulation robustness. The quasi-1D solver has shown good qualitative agreement with the multidimen- sional data obtained from URANS simulation and quantitative agreement with the hybrid RANS-LES data, encouraging further developments of the low order model that most likely include extraction of response functions from experimental data.