Computational analysis of incompressible turbulent flow in an idealised swirl combustor (original) (raw)
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Computational Analysis of Isothermal Flow in a Test Swirl Combustor
Isothermal flow in an idealized swirl combustor is analyzed numerically and experimentally. The Reynolds number based on combustor inlet diameter and mean axial velocity is 4600. Measurements of time-averaged swirl and axial velocity components and corresponding rms turbulence intensities are performed by Laser Doppler Anemometry, along radial traverses at different axial locations. In three-dimensional, transient computations, Large Eddy Simulations (LES) and Unsteady Reynolds Averaged Numerical Simulations (URANS) are employed for modeling the turbulent flows. For LES, the Smagorinsky model is used to model the subgrid scale turbulence. For URANS, the Reynolds Stress Model (RSM) is employed as the statistical turbulence model. The URANS-RSM approach is observed to perform rather poorly. This is assumed to be due to the fact that the present flow has a rather low Reynolds number, and the applied RSM, being a high Reynolds number model, is not able to model low Reynolds number effec...
Experimental Thermal and Fluid Science, 2017
Swirling flows through sudden expansions is a common solution adopted to stabilise the flame within combustion systems. Fuel-air mixing promoted by the swirling motion contributes also to complete the fuel oxidation and reduce pollutant emissions. Most of the experimental studies appeared in the literature investigated the aerodynamics of highswirl combustors. In such combustors the expansion of the flow in the combustion chamber produces a central recirculation zone (CRZ) which provides a stable anchoring to the flame. By comparison, few studies analyse the structure of the flow field with weak swirl, although the capability of lowswirl combustors to generate stable flames over a wide range of thermal loads was experimentally demonstrated. This study deals with low-swirling flows generated by axial swirlers and aims at providing a comprehensive insight of the flow field by considering the effect of some relevant parameters not yet systematically investigated. Data taken from the literature of axial and tangential velocities measured on combustors of similar geometry and swirl number are compared in order to evaluate the effect of the Reynolds number and the main design parameters on the flow field. The literature database is 2 extended considering original measurements performed by the authors on a laboratory combustor.
Numerical Analysis of Turbulent Combustion in a Model Swirl Gas Turbine Combustor
Journal of Combustion, 2016
Turbulent reacting flows in a generic swirl gas turbine combustor are investigated numerically. Turbulence is modelled by a URANS formulation in combination with the SST turbulence model, as the basic modelling approach. For comparison, URANS is applied also in combination with the RSM turbulence model to one of the investigated cases. For this case, LES is also used for turbulence modelling. For modelling turbulence-chemistry interaction, a laminar flamelet model is used, which is based on the mixture fraction and the reaction progress variable. This model is implemented in the open source CFD code OpenFOAM, which has been used as the basis for the present investigation. For validation purposes, predictions are compared with the measurements for a natural gas flame with external flue gas recirculation. A good agreement with the experimental data is observed. Subsequently, the numerical study is extended to syngas, for comparing its combustion behavior with that of natural gas. Here...
Computational Investigation of Turbulent Swirling Flows in Gas Turbine Combustors
International Journal of Fluid Machinery and Systems, 2008
In the first part of the paper, Computational Fluid Dynamics analysis of the combusting flow within a high-swirl lean premixed gas turbine combustor and over the 1 st row nozzle guide vanes is presented. In this analysis, the focus of the investigation is the fluid dynamics at the combustor/turbine interface and its impact on the turbine. The predictions show the existence of a highly-rotating vortex core in the combustor, which is in strong interaction with the turbine nozzle guide vanes. This has been observed to be in agreement with the temperature indicated by thermal paint observations. The results suggest that swirling flow vortex core transition phenomena play a very important role in gas turbine combustors with modern lean-premixed dry low emissions technology. As the predictability of vortex core transition phenomena has not yet been investigated sufficiently, a fundamental validation study has been initiated, with the aim of validating the predictive capability of currently-available modelling procedures for turbulent swirling flows near the sub/supercritical vortex core transition. In the second part of the paper, results are presented which analyse such transitional turbulent swirling flows in two different laboratory water test rigs. It has been observed that turbulent swirling flows of interest are dominated by low-frequency transient motion of coherent structures, which cannot be adequately simulated within the framework of steady-state RANS turbulence modelling approaches. It has been found that useful results can be obtained only by modelling strategies which resolve the three-dimensional, transient motion of coherent structures, and do not assume a scalar turbulent viscosity at all scales. These models include RSM based URANS procedures as well as LES and DES approaches.
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Energy & Fuels, 2016
In this work, numerical investigation of a gas turbine model combustor (GTMC) was carried out using two different turbulence-chemistry interaction models: the EDC (Eddy Dissipation Concept) and TPDF (Transported Probability Density Function). GTMC with a good optical access for laser measurements provides a useful database for swirling CH ସ /Air diffusion flames at atmospheric pressure. Modeling was performed by solving RANS and RSM equations for a 2D axisymmetric computational domain accompanied with swirl and the combustion chamber was investigated for both reacting and non-reacting conditions. A detailed reduced mechanism of DRM22 (with 22 species and 104 reactions) was used to represent the chemical reactions. Comprehensive comparisons were done for the predictions and measurements of velocity, mixture fraction, temperature, and chemical species concentrations of H ଶ , O ଶ , OH, H ଶ O, CH ସ , CO, and CO ଶ. Results showed an acceptable accuracy of predictions by considering computational cost. That means that the simplified 2D-axismmetric-swirl simulation has the ability to capture some important features and structure of combustion field in a double highly swirled chamber, like GTMC, with much lower CPU time in comparison with costly 3D modellings, although misses some details of flow field characteristics in comparison with more accurate LES approach. In terms of comparison between the turbulence-chemistry interaction models, TPDF led to a good prediction for major species and flame structure near the inlets while the EDC predicted more accurately downstream of the flow field.
Nonuniform combustor outlet flows have been demonstrated to have significant impact on the first and second stage turbine aerothermal performance. Rich-burn combustors, which generally have pronounced temperature profiles and weak swirl profiles, primarily affect the heat load in the vane but both the heat load and aerodynamics of the rotor. Lean burn combustors, in contrast, generally have a strong swirl profile which has an additional significant impact on the vane aerodynamics which should be accounted for in the design process. There has been a move towards lean burn combustor designs to reduce NO x emissions. There is also increasing interest in fully integrated design processes which consider the impact of the combustor flow on the design of the high pressure vane and rotor aerodynamics and cooling. There are a number of current large research projects in scaled (low temperature and pressure) turbine facilities which aim to provide validation data and physical understanding to support this design philosophy. There is a small body of literature devoted to rich burn combustor simulator design but no open literature on the topic of lean burn simulator design. The particular problem is that in non-reacting, highly swirling and diffusing flows, vortex instability in the form of a precessing vortex core or vortex breakdown is unlikely to be well matched to the reacting case. In reacting combustors the flow is stabilized by heat release, but in low temperature simula-tors other methods for stabilizing the flow must be employed. Unsteady Reynolds-averaged Navier–Stokes and large eddy simulation have shown promise in modeling swirling flows with unstable features. These design issues form the subject of this paper.