ISBN 9783843941815

978-3-8439-4181-5, Reihe Energietechnik

Sohail Iqbal
Numerical investigation of turbulent combustion in gas turbine combustors for methane, biogas and syngas fuels

108 Seiten, Dissertation Helmut-Schmidt-Universität Hamburg (2018), Softcover, A5

Zusammenfassung / Abstract

Numerical simulation of swirling flames in gas turbine combustors is an important part of gas turbine design and is the focus of this work. The swirling flow in the combustors is used to generate a vortex breakdown recirculation zone which helps in the flame stabilization. Therefore in this work, numerical simulation of the swirling flow is performed with the focus on the turbulence modelling for high Re number flows. For this purpose, RANS and LES turbulence models were used and the results are compared with the measurements. Overall, LES model shows better agreement with the experiments but is more computationally intensive because of higher number of elements. DES simulations also performed well, however, there was no significant improvement compared to LES. An optimum grid size was obtained with respect to quality of agreement with the measurements and computational time by employing theoretical criterion. The resulting grid was then used to study the turbulent swirling methane-air flames in gas turbine combustors with Re number representative of the practical gas turbine combustors. The focus was to investigate turbulence-chemistry interaction in reacting flows to model the flow field and temperature and mixing of fuel-air streams in diffusion flames. The EDC and FLAMELET combustion models were used to simulate the non premixed swirling flames and validation was done with the experimental data. Both combustion models showed good agreement with the measurements but EDC exhibited longer computational time which makes its use in industrial applications challenging.

The numerical simulations were performed for a fuel flexible experimental combustor test-rig with natural gas, biogas and syngas as fuels. The numerical results showed that the syngas flames exhibited the tendency to propagate upstreams which was also observed in the experiments. The flue-gas recirculation is a promising technology to reduce the CO2 emissions where a part of the exhaust air is recirculated to inlet air stream of the compressor. Flames of natural gas, biogas and syngas fuels operated under different levels of flue-gas recirculation were simulated and the CO2 and NOx emissions were compared with the experimental data. The effect of the increasing FGR showed an increase in exhaust CO2 and NOx emissions. The absolute value of the exhaust CO2 and NOx obtained with simulations showed significant deviation from the experimental data.