| 1. |
- Gherman, Bogdan, George, et al.
(författare)
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LES of swirling flows in gas turbine combustion chambers
- 2004
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Ingår i: Proceedings of the ASME Turbo Expo 2004. ; 1, s. 465-473
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Konferensbidrag (refereegranskat)abstract
- The flow and mixing in a swirl-stabilized gas-turbine burner is studied by Large Eddy Simulations (LES). Each swirler has a different mass flux and swirl angle. The interaction between neighbouring jets is studied, co-rotating and counter rotating jets are considered. Another issue of importance is related to the jet inlet conditions (e.g. axial distribution and levels of turbulence). In addition to the flow field (using LES) we present results related to fuel/air mixing under different conditions. We show that the LES results can resolve several issues related to the burner that cannot be accounted for by the standard RANS computations.
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| 2. |
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| 3. |
- Mihaescu, Mihai, et al.
(författare)
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Modeling of the acoustical field due to a jet engine with ground effect
- 2003
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Ingår i: Proceedings of the Tenth International Congress on Sound and Vibration. ; , s. 677-684
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Konferensbidrag (refereegranskat)abstract
- The principal noise source for a jet engine is associated with the jet exhaust. The acoustical field that is generated by a jet engine before the take-off is considered. The turbulent jet and the mixing of the hot exhaust gas with the cold surrounding air forms an acoustical source. The compressible Navier-Stokes equations describe both flow field as well as sound generation. The acoustic theory uses the hypothesis that a part of the flow field (which is the source of the acoustic field) is distinct from the properties of the ambient flow field. Thus, the velocity vector, the pressure and the density are split into semi-compressible components and inviscid, irrotational acoustical components. The turbulent flow and mixing are computed by using Large Eddy Simulation (LES). The instantaneous LES provide the acoustical source for the Lighthill's wave equation, which is used to compute the acoustical field. The computed acoustical field agrees quite well with published experimental data.
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| 4. |
- Mihaescu, Mihai, et al.
(författare)
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Noise computation of a turbo-engine jet exhaust based on LES and lighthill's acoustic analogy
- 2004
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Ingår i: Proceedings of the ASME Turbo Expo 2004. - : ASME. ; 5 B, s. 1723-1731, s. 1723-1731
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Konferensbidrag (refereegranskat)abstract
- Increasing noise regulations at urban airports force jet engine manufactures to develop and build more quiet engines. Over recent years, a significant reduction in fan and mechanical noise has been achieved. However, the jet exhaust is the principal source of noise. The acoustical field that is generated by a turboengine jet exhaust running near the ground level is considered. The full equations of motion for compressible and unsteady flows describe both flow field and sound generation. The flow variables are decomposed into semi-compressible components and inviscid, irrotational acoustical components. The turbulent flow and mixing are computed using Large Eddy Simulation (LES). The radiated acoustical field is computed using the Lighthill's acoustic analogy with acoustic sources provided by instantaneous LES data.
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| 7. |
- Szász, Robert-Zoltán
(författare)
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Numerical Modeling of Flows Related to Gas Turbine Combustors
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis focuses on the numerical simulation of the flow field in gas turbine burners. Due to tougher and tougher requirements on low levels of emission of pollutants there is a need for new combustion technologies. In gas turbines one method to attain low pollutant levels is the use of lean premixed combustion. However, in lean combustion, problems related to the flame stability can arise. Swirling jets can be used to assure flame holding by forming an internal recirculation zone which helps to re-ignite the eventually extincted flame. Additionally, the swirl is enhancing the mixing process. This is important not only for flame stability and efficiency of combustion, but also the NOx levels have been proved to be highly dependent on the local mixture composition. Swirling flows, however, are difficult (but not impossible) to examine experimentally because of the high sensitivity of the flow field to external conditions. In addition, experimental approaches cannot be used to study the effects of individual parameters. Consequently, the use of accurate numerical methods is preferred for analysis and design. Of course, the accuracy of the numerical tools and the design must be verified by experiments. Here, the flow field downstream of a burner providing three swirling coaxial jets is studied numerically. The turbulence is accounted for by the Large Eddy Simulation (LES) approach because RANS-based models have been proved to fail to account accurately for some characteristics of the swirling flows, like large streamline curvature, flow reversal and flow dynamics. Since only limited experimental data exists for the given combustion chamber, the computational approach is tested first on a test case involving a single swirling jet. Further, the flow fields obtained by altering different parameters (Reynolds number, swirl number, inlet velocity profile, confinement) are compared with the base case in order to evaluate the importance of each parameter in the present set-up. These parameters are important for an efficient flow control. A study of the turbulent mixing in the combustion chamber is also presented. The effect of Schmidt number has been studied and the presence of counter gradient diffusion is established. The acoustic field generated by the swirling jet has been evaluated in order to identify resonant frequencies of the flow.
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| 8. |
- Szász, Robert-Zoltán
(författare)
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Numerical modeling of Swirling Flows in Gas Turbine Burners
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis focuses on the numerical simulation of the flowfield in gas turbine burners. Due to the higher and higher requirements regarding pollutant emissions there is a need for new combustion technologies. In gas turbines one method to obtain low pollutant levels is the use of lean premixed or partially premixed combustion. However, in lean combustion problems regarding the flame stability can arise. Swirling jets can be used to assure flame stabilization by forming an internal recirculation zone which helps to re-ignite the eventually extincted flame. Additionally, the swirl is enhancing the mixture quality. This is important not only for flame stability and efficiency of combustion, but also the $NO_x$ levels have been proved to be highly dependent on the local mixture composition. Swirling flows, however, are difficult to examine experimentally because of the high sensitivity of the flowfield to external conditions. In addition, experimental approaches demand larger resources and are limited in studying effects of individual parameters. Consequently, the use of numerical methods is preferred for analysis and design. Of course, the design should be validated by experiments. Here, the flowfield downstream of a burner providing three swirling coaxial jets is studied numerically. The turbulence is accounted for by the Large Eddy Simulation approach because simpler methods has been proved to fail to account accurately for some characteristics of the swirling flows, like large streamline curvature and flow reversal. The spatial derivatives are discretized with high-order schemes ($3rd$ and $4th$ order). Because no experimental data exist for the given combustion chamber, the computational approach is tested first on a testcase involving a single swirling jet. Later, the flowfields obtained by altering different parameters (Reynolds number, swirl number, inlet velocity profile, confinement) are compared with a base case in order to evaluate the importance of each parameter in the present set-up. A study of the turbulent mixing in the combustion chamber is also presented. The effect of Schmidt number will be studied and the presence of counter gradient diffusion is established.
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