b'Power & Energy | Engineer Innovation28 million cells, most of which are distributed in the swirler, mixing and reaction regions. The cell size in the flame region and most of the mixing region was less than one millimeter.When compared with experimental observations on the same rig the LES results showed good agreement, and predicted the principle mechanisms that ultimately are the cause of thermo-acoustic oscillations:The LES predictions show good overall agreement with experimental data in terms of the mean flame structure and pressure fluctuations that are produced.Figure 3: Computational mesh used for LES simulationsMore than this, the simulations revealed the mechanisms behind the pressure fluctuations we observed on the rig,Beyond fossil fuelssaid Dr Moll. Axial movements of theAlthough natural gas (principally flame are coupled with the pressuremethane) is by far the most commonly drop across the burner and the localused fuel for gas turbines, attention is swirl number, acting as a force/increasingly turning to synthetically feedback loop between velocity,generated non-fossil fuel gases, such as pressure, and local flame position. Thehydrogen and ammonia. These can be axial flame pulsating is interacting withmixed with methane in order to further an acoustic mode generating axialreduce COemissions. However, 2pressure fluctuations in the combustionchanging fuel mixes is another potential chamber. cause of thermo-acoustic instability, something else that LES simulations can In addition to the two dominant axialenhance insight into:pressure fluctuation modes, a mode acting in the cross direction of theUnderstanding this coupling between combustion chamber is discovered,fuel and transient flow effects is of key continued Dr Moll. This pressure waveimportance to gas turbine developers, is bouncing between two of the foursaid Dr Moll. On a global level, using combustion chamber walls and isdifferent fuels results in different flame triggered by the general flameshapes and different flame positions movements - which is one of the things that we can easily simulate using CFD, but it is very Once validated, the Simcenter STAR- difficult to measure on a test-rig. We CCM+ simulations provided a wealth ofcan also predict changes in dynamic insight and engineering data: response that will alter the thermo-acoustic behavior of the system by The real value of CFD is to explain theusing a different fuel, where the heat dynamic effects because we have all ofrelease is slightly different. the necessary data in the flow field. Once you have demonstrated the CFDThe possibilities are endless herefor result matches the experiment, you canexample another way of dealing with go into much more detail inthe intermittent nature of wind could investigating flow phenomena throughbe to use excess wind-power to post-processing and data analysis, saidmanufacture hydrogen which could be Dr Moll. You can look at the detailedused as pure fuel for electricity coupling between vortex structures,producing gas turbines that run at heat release, and acoustics. You cannight, without COemission. Of course, 2then start to answer the importantthe different chemical properties of a questions: how can I change the flowhydrogen flame might then lead a field to improve the dynamicchanged combustion behavior, which performance of my gas turbine, withalso need to be mitigated using LES CFD fewer emissions and more stability? simulations.9'