Numerical Procedure for the Investigation of Combustion Dynamics in Industrial Gas Turbines: LES, RANS and Thermoacoustics

Abstract

The necessity for a combustion system to work with premixed flames and its capability to cope with rapid load variations avoiding the occurrence of thermo-acoustic instabilities, has led to investigate the complex dynamic phenomena that occur during combustion. Thanks to numerical simulations it is possible to examine these complex mechanisms getting useful information to optimize the combustion system. The aim of this work is to describe a numerical procedure developed in Ansaldo Energia for the investigation of combustion dynamics occurring in Ansaldo Energia gas turbines. In this paper, firstly the experimental apparatus of a full scale atmospheric test rig equipped with Ansaldo Energia burner is described. Secondly, the flame behavior is studied by means of a Large Eddy Simulation (LES). Once the LES has reached a statistically stationary state, a forcing is added to the system to compute the Flame Transfer Function (FTF), in terms of amplitude n and delay time τ, related to initial phases of humming. Thirdly, the forced flame simulations are used as the input of an Helmholtz solver to analyze the acoustic behavior of the system, which is then compared to experimental data. Finally, to evaluate the feasibility of a less computationally intensive approach, a RANS simulation of the same configuration is described and the results are transferred to FEM (Finite Element Method) Helmholtz solver: a comparison between the LES approach and the RANS approach is carried out with reference to the experimental data.

Comparison of Hydrogen Micromix Flame Transfer Functions Determined Using RANS and LES

“…The amplitude and frequencies chosen are shown in Table 3. An alternative forcing method has also been investigated in which multiple forcing frequencies are superimposed onto a single velocity perturbation which has been successfully applied in thermoacoustic assessments of premixed flames in industrial gas turbines [43]. This method also influenced the choice of forcing frequencies as it was essential that they were sufficiently distributed in such a way that harmonics of the lower forcing frequencies were not close to any of the higher forcing frequencies.…”

Numerical and experimental studies on self sustained thermo-acoustic combustion instabilities of an experimental rig for full-scale industrial burners

“…The longitudinal rig analyzed in this work has been thoroughly used to study the dynamics full-scale burners [11][12][13][14]. It comprises of two cylindrical chambers, the plenum and the combustion chamber, coupled by the burner.…”

“…Reynolds Average Navier Stokes (RANS) simulations are performed in order to calculate the three-dimensional fields of the thermodynamics quantities of the baseline flow. The six species-three reactions 2sCM2 combustion scheme has been used to simulate the combustion process [4,13]. Fig.…”

“…2(b), it is possible to notice that the first part of the flame front is located within the CBO that is included in the computational domain. Further details of these RANS simulations and a comparison between results from LES simulations can be found in [13]…”

Two-step approach for pressure oscillations prediction in gas turbine combustion chambers

“…There are different methods and numerical tools for prediction of combustion instabilities occurrence. The numerical tools used for thermoacoustic analysis could be divided into two groups: those that perform frequency domain analysis [4][5][6] and those that make time-domain simulations. 7,8 The first type of analysis can be applied to complex geometries of combustion chambers.…”