Benim, A.C.
(Department of Mechanical and Process Engineering, Duesseldorf University of Applied Sciences)
,
Escudier, M.P.
(Department of Engineering, University of Liverpool)
,
Stopford, P.J.
(ANSYS Europe Ltd.)
,
Buchanan, E.
(Combustor Development, Siemens Industrial Turbomachinery Ltd.)
,
Syed, K.J.
(Combustor Development, Siemens Industrial Turbomachinery Ltd.)
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 com...
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.
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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제안 방법
The solution domain is defined to start in the annular channel, slightly upstream of the combustor. Preliminary 3D RANS computations were performed for a domain covering the guide vanes of the swirl generator and the axial inlet channel. In the main computations, the block-structured grid with conformal block interfaces consisted of approximately 600,000 hexa cells.
The solution domain is defined to include the combustor and the swirl generator. Preliminary 3D RANS computations were performed for a domain covering the plenum and channels of the swirl generator to obtain the inlet conditions. For the main computations, the block-structured grid consisted of approximately 1,000,000 hexahedral finite volumes.
The experimental data shows a forced-vortex-like region in the vicinity of the axis, changing over to a free-vortex-like distribution at higher values of the radial coordinate. It is interesting to note that the vortex core first radially expands between the stations x=10mm and x=50mm, and then contracts between x=50mm and x=160mm.
Although many analytical and numerical investigations have been conducted to address vortex breakdown and the criticality of the vortex core [3-6] much of this work is based upon simplifying assumptions, such as axisymmetry in conjunction with a Reynolds Averaged Navier-Stokes (RANS) based turbulence modelling. These studies have revealed much about the behaviour of vortical flows but they fall short of delivering quantitative information that can be used in the design of combustors, since low- frequency transient motion of coherent structures, which can play a very important role in swirling flows, cannot be represented adequately by a RANS based turbulence modelling approach.
대상 데이터
Preliminary 3D RANS computations were performed for a domain covering the plenum and channels of the swirl generator to obtain the inlet conditions. For the main computations, the block-structured grid consisted of approximately 1,000,000 hexahedral finite volumes.
Preliminary 3D RANS computations were performed for a domain covering the guide vanes of the swirl generator and the axial inlet channel. In the main computations, the block-structured grid with conformal block interfaces consisted of approximately 600,000 hexa cells.
The experimental results show recirculation regions as well as on the axis, and in the corner downstream of the sudden expansion into the combustor, at the axial stations x=10mm and x=50mm. At x=160mm, it can be observed that both recirculation zones have disappeared, and, on the axis, the reverse flow zone is replaced by a strong jet-like overshoot.
이론/모형
Although many analytical and numerical investigations have been conducted to address vortex breakdown and the criticality of the vortex core [3-6] much of this work is based upon simplifying assumptions, such as axisymmetry in conjunction with a Reynolds Averaged Navier-Stokes (RANS) based turbulence modelling. These studies have revealed much about the behaviour of vortical flows but they fall short of delivering quantitative information that can be used in the design of combustors, since low- frequency transient motion of coherent structures, which can play a very important role in swirling flows, cannot be represented adequately by a RANS based turbulence modelling approach.
In the first part of the paper, it is demonstrated that very encouraging results can indeed be obtained for a high-swirl lean premixed gas turbine combustor flow, which qualitatively agree with the measurements [7], applying an Unsteady RANS (URANS) based turbulence modelling approach, utilizing a Reynolds Stress Model (RSM) as the statistical turbulence model.
DES: Detached Eddy Simulations [15,16], as a LES-RANS hybrid modelling approach. In the present application, the model is based on the Shear Stress Transport (SST) model of Menter [17] as the background RANS model.
The rig operates at Re=7000 (Reynolds number is based on the diameter and the bulk axial velocity of the combustor). Measurements were performed by Laser Doppler Anemometry (LDA). Different swirl levels were obtained by adjusting the swirler guide vanes angles.
The analysis has been based on the commercial general-purpose CFD software ANSYS-CFX [8]. It is already known [9] that certain Reynolds stress components are significantly modified due to the action of flow curvature and pressure gradient within swirling flows.
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