Lean Direct Injection Gas Turbine Research Articles

Influence of liquid-fuel swirl injection pressure on the flow dynamics characteristics in a lean direct injection gas turbine combustor using Eulerian-Lagrangian large eddy simulations

Influence of liquid-fuel swirl injection pressure on the flow dynamics characteristics in a lean direct injection gas turbine combustor using Eulerian-Lagrangian large eddy simulations

Thermoacoustic instability and flame transfer function in a lean direct injection model gas turbine combustor

This paper discusses the combustion dynamic characteristics of hydrogen/methane flames and the flame response to fuel flow fluctuation in a model lean-direct injection gas turbine combustor. The results show that a higher frequency longitudinal thermoacoustic instability is triggered as hydrogen/methane ratios increase. The mode shift is accompanied by shortening flame length and hence decreasing convection time delay between fuel injection and flame location. The flame transfer function (FTF) subject to fuel flow rate modulation is determined over a range of frequencies for hydrogen/methane volume ratios of 25:75, 50:50, and 75:25 at a fixed equivalence ratio of 0.55. The input and output of the FTF are the velocity fluctuation of fuel-mixture at the inlet of the burner and the heat release fluctuation of flame in the combustion zone, respectively. Because of the difficulty of measuring fuel flow velocity at the inlet of the combustor while the flame exists, the fuel transfer function (FLTF) is measured and used along with the intermediate flame transfer function (ITF) to determine the FTF. The transfer functions are measured at frequencies up to 600 Hz and the FTF above 600 Hz is determined from the flame response at higher harmonic frequencies. Results of the FLTF measurement show that an acoustic resonance is formed within the fuel injector and the resonance frequency changes with the hydrogen/methane ratio as well as the length of the fuel feedline. The gain of FTF at a given frequency decreases as the hydrogen content increases and the absolute value of the slope of the phase plot, which is related to the convection time delay between fuel injector tip and flame location, decreases as the hydrogen enrichment ratio increases. Using the measured FTF as input to an open-source simulator, the occurrence of instability is predicted and compared with experimental results. The modeling results agree very well with the experimental data in predicting the occurrence of unstable combustion, the frequency at which unstable combustion occurs, and the acoustic mode inside the combustor.

Vortex breakdown of the swirling flow in a Lean Direct Injection burner

This paper presents a comprehensive study of the unsteady flow field in a new concept lean direct injection gas turbine burner, which aims at a clean and efficient combustion with application to sustainable aviation and pollution abatement. Large Eddy Simulation (LES) and planar particle image velocimetry are employed to capture the characteristics of the swirling flow issued from the multiple-jet swirler under both the confined and unconfined conditions. The results are compared, and good agreement shows the capability of LES in capturing the large-scale flow structures. The iso-contour of axial and swirl velocities shows that the swirling flow is featured by multiple jets. These jets interact with the central recirculation zone (CRZ) and reform it into a “starfish” shape. Under the effect of the confinement, the flow displays a larger spreading angle of the jets and an outer recirculation zone (ORZ). A distinctive connection between the CRZ and the ORZ is evidenced to occur through the channels between the multiple jets. The outward flow in the channels is identified to oscillate at a Strouhal number of 0.1. To characterize the evolution, the unsteady large-scale structures, proper orthogonal decomposition (POD), and spectra POD (SPOD) analyses are performed. It is found that a single helix and a double helix are manifestations of two independent global modes in the SPOD analysis. The former shares the same frequency with the outward flow, and the latter is solely affected by the confinement.

Modeling gaseous non-reactive flow in a lean direct injection gas turbine combustor through an advanced mesh control strategy

Fuel efficiency improvement and harmful emissions reduction are the main motivations for the development of gas turbine combustors. Numerical computational fluid dynamics (CFD) simulations of these devices are usually computationally expensive since they imply a multi-scale problem. In this work, gaseous non-reactive unsteady Reynolds-Averaged Navier–Stokes and large eddy simulations of a gaseous-fueled radial-swirled lean direct injection combustor have been carried out through CONVERGE™ CFD code by solving the complete inlet flow path through the swirl vanes and the combustor. The geometry considered is the gaseous configuration of the CORIA lean direct injection combustor, for which detailed measurements are available. The emphasis of the work is placed on the demonstration of the CONVERGE™ applicability to the multi-scale gas turbine engines field and the determination of an optimal mesh strategy through several grid control tools (i.e., local refinement, adaptive mesh refinement) allowing the exploitation of its automatic mesh generation against traditional fixed mesh approaches. For this purpose, the normalized mean square error has been adopted to quantify the accuracy of turbulent numerical statistics regarding the agreement with the experimental database. Furthermore, the focus of the work is to study the behavior when coupling several large eddy simulation sub-grid scale models (i.e., Smagorinsky, Dynamic Smagorinsky, and Dynamic Structure) with the adaptive mesh refinement algorithm through the evaluation of its specific performances and predictive capabilities in resolving the spatial-temporal scales and the intrinsically unsteady flow structures generated within the combustor. This investigation on the main non-reacting swirling flow characteristics inside the combustor provides a suitable background for further studies on combustion instability mechanisms.