Simulation and Control of Instationary Reactive Flows in Matrix Burner for Small Power Gas Turbine Applications

The main objective of this thesis is to analyze combustion instabilities in a matrix

burner. The various tools that exist for analyzing thermoacoustic instabilities are

applied to the matrix burner with multiple flames. The principal goals are to determine

the primary causes of combustion instabilities in the burner and to explore

ways of controlling such instabilities in order to prevent damage to the burner.

To achieve these goals, the stability map of the burner obtained from measurements

is analyzed. This is followed by the analysis of the aerodynamics of the cold flow

using CFD. Results obtained from CFD are validated with PIV and LDA results

from measurements. Critical are the centerline axial velocity inside the combustion

chamber and the recirculation zones on the walls of the combustion chamber and

those between the various slots of the matrix burner.

Cold flow simulations are followed by reactive flow simulations for both gaseous and

liquid fuels. A detailed atomization model is developed for the liquid fuel case from

experimental data. Two combustion models, namely, the combined finite rate/eddy

dissipation model and the finite rate chemistry model are compared in the CFD

simulations of combustion instabilities and validation with measurements are done.

The latter is chosen over the former because it accounts for chemistry and it is not

numerically dissipative. Two CFD softwares, Fluent and CFX are also compared to

determine which is better at capturing acoustics. System identification using CFD

is used to determine the flame transfer function and the acoustic transfer matrix.

This is followed by the use of acoustic forcing and fuel modulation on the primary

and pilot in order to limit the amplitude of the instabilities inside the matrix burner

combustor.

The 1D acoustic network is used to determine the longitudinal eigenmodes of the

matrix burner. This is followed by the use of 3D finite element method (FEM) and

fluid-structure interaction (FSI) to determine whether a coupling exist between the

fluid and structure of the matrix burner combustor and vice versa.

Finally, Full harmonic analysis is performed for the rectangular combustor and the

results obtained are validated with analytical results. This is followed by the 3D

structure modal analysis of the full matrix burner test rig.