| 1. |
- Iudiciani, Piero, et al.
(författare)
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Characterization of a multi-swirler fuel injector using simultaneous laser based planar measurements of reaction zone, flow field and fuel distribution
- 2009
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Ingår i: Proceedings Of The Asme Turbo Expo 2009, Vol 2. - 9780791848838 ; 2, s. 1041-1052
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Konferensbidrag (refereegranskat)abstract
- Modern gas turbine spray combustors feature multiple swirlers with distributed fuel injection system for rapid fuel/air mixing and flame stabilization ensuring low NOx operations. In the present paper, we investigate the effects of different swirler designs on flame characteristics, stabilization, and behavior at lean blow out using a Triple Annular Research Swirler (TARS) burner. Simultaneous planar measurements using laser diagnostics, namely, Planar Laser Induced Fluorescence (LW) of OH radicals indicating the reacting zone, LW Acetone indicating unburnt fuel distribution and Particle Image Velocimetry (PIV) for flow field mapping, were applied to study the flow dynamics, fuel distribution and flame dynamics for different swirler geometries, air flow rates, and equivalence ratios. Both axial and nearly perpendicular to axis cross-sectional planes were investigated. The three swirler configurations allowed getting stable and repeatable flames over a wide range of different flow and fuel equivalence ratio conditions, confirming the good flexibility and operability of the TARS burner. Averaged fields are presented to compare the effect of different flow conditions using the same swirler configuration, and the effect of different swirler configurations at the same flow conditions. LIF and PIV instantaneous samples are also shown, both in axial and cross sectional planes, with structures captured in detail. Perfect matching is found between unburnt and burnt field, as well as agreement between axial and cross-sectional measurements. Particular attention has been placed on unstable flames and a highly unsteady flame near the lean blow out (LBO) is shown. Local extinctions are occasionally seen on instantaneous snapshots. Unsteadiness of such flame is suitable to exemplify the use of Proper Orthogonal Decomposition (POD) analysis that identifies the most "energetic" large scale structures or modes of the flame. In particular, rotational and helical modes are observed which can contribute to the swirling flame instability. The results show the effect of the strength and rotation direction of the swirlers can lead to strong flame stratification or to a more homogenous flames. Analysis of the flame dynamics, indicates that the flame can be stabilized dynamically without the presence of a Central Recirculation Zone (CRZ) through flame quenching and flame propagation.
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| 2. |
- Duwig, Christophe, et al.
(författare)
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Large Eddy simulation of a swirling flame response to swirl modulation with impact on combustion stability
- 2005
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Ingår i: 43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers. ; , s. 4929-4940
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Konferensbidrag (refereegranskat)abstract
- A swirl stabilized flame has been studied numerically using Large Eddy Simulation. The response of the flame to a large swirl number modulation has as been determined. Decreasing the swirl number moderately does not destabilize the flame. Decreasing further the swirl number induces a transition from stabilized to a jet flame with increase in the flame fluctuations. Increasing back the swirl restores the original configuration. However, the re-stabilization has been found to be considerably slower as compared to the burner aerodynamic time scale. Further studies, including identification of some characteristic turbulent structures, have been carried out. Both a helical and an axial mode have been identified. The helical mode arises in the central recirculation zone, whereas the axial mode arises in the outer shear-layer. Both modes are possible sources of thermo-acoustic instabilities.
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| 3. |
- Duwig, Christophe, et al.
(författare)
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Modelling of flameless combustion using large eddy simulation
- 2006
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Ingår i: Proceedings of the ASME Turbo Expo 2006, Vol 1. - 0791842363 ; , s. 31-40
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Konferensbidrag (refereegranskat)abstract
- The challenge of achieving a clean and stable combustion in modem power plants or aero engines leads to develop new technologies and new combustors. Pioneer work on 'flameless' combustion has shown the great potential of such a technology for meeting modem requirements in term of safety and. low emissions. The idea behind this technique is to ensure low emissions by operating at very low fuel/air equivalence ratio but with high preheating to stabilize the combustion. In addition, a careful design of the combustor should ensure that fresh gases are diluted by hot exhaust gases. The result is a distributed but efficient oxidation region. This paper presents a new efficient model for simulating 'flameless' oxidation. The model is based on Large Eddy Simulation (LES) ensuring an accurate description of the mixing. In addition, a 'low-cost' technique for coupling the LES code with some complex chemistry is presented. This approach was used for simulating a reacting jet close to the 'flameless' regime. The simulation showed the capability of the present LES tool for understanding the flow dynamics and improving the design of 'flameless' combustors.
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| 4. |
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| 5. |
- Mihaescu, Mihai, et al.
(författare)
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Coaxial jet noise prediction: Grid resolution effect on the numerical solution
- 2005
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Ingår i: Collection of Technical Papers - 11th AIAA/CEAS Aeroacoustics Conference. - : AIAA. - 1563477300 ; 5, s. 3586-3595, s. 3586-3595
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Konferensbidrag (refereegranskat)abstract
- The flow and acoustic fields that are generated by two coaxial jets are considered. The problem is handled by solving the flow field using Large Eddy Simulation (LES) and the acoustics by a wave equation with source terms provided by the instantaneous LES. The paper is focused on the influence of the grid resolution on the solution accuracy.
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| 6. |
- Mihaescu, Mihai, 1976-, et al.
(författare)
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Computational Aeroacoustics of a Separate Flow Exhaust System with Eccentric Inner Nozzle
- 2007
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Ingår i: 45th AIAA Aerospace Sciences Meeting 2007. - 9781563478901 ; , s. 28-39
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Konferensbidrag (refereegranskat)abstract
- A major issue related to our modern way of life is the noise caused by jet engine powered airliners. Methods to reduce the jet noise were proposed in the last decades starting with the introduction of high bypass turbofan engines. A numerical investigation of flow and acoustics of a separate flow exhaust system is performed in the present paper. The goal is to investigate how the noise generated by a separate flow jet engine exhaust is influenced if the symmetry of the jet exhaust geometry is broken by having the inner nozzle and the center body off the center line axis of the fan nozzle. A decomposition of flow variables is used that allows separation of flow and acoustic computations. Large Eddy Simulation approach is employed to compute the flow field and the acoustic sources. The inhomogeneous wave equation is used to compute the acoustic near- and far-fields. Using this method, previous numerical studies of the symmetric (baseline) configuration showed good agreement between the computed data and the experimental results. Comparisons between the near- and far-field baseline concentric case and the computations obtained using the eccentric configuration are performed showing an acoustic benefit for the offset case.
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| 7. |
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| 8. |
- Mihaescu, Mihai, et al.
(författare)
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Flow and noise investigations of a separate flow exhaust system
- 2005
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Ingår i: Proceedings of the ASME Turbo Expo. - : ASME. ; 6 PART B, s. 1221-1229, s. 1221-1229
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Konferensbidrag (refereegranskat)abstract
- A major component of aircraft noise is the jet noise created by the high velocity hot stream exhausting from a jet engine, interacting with itself and with the surrounding cold air. In the present paper the flow and acoustic fields that are generated by two coaxial jets are considered. Numerically, the problem is divided into a flow related part (Navier-Stokes system of equation) and an acoustic part (an inhomogeneous wave equation). The flow field is handled by well resolved Large Eddy Simulation (LES). The acoustical sources can then be computed from the flow field calculations, on the near-field "source" grid. The acoustic field is solved, on the same or even on a larger separate grid, by using an acoustic approximation with appropriate acoustic boundary conditions. The computed flow and acoustical fields are compared to those measured on the separate flow nozzle test facility. The comparisons in terms of velocity and sound pressure levels are shown to validate the used approach. Frequency spectra of the acoustic density fluctuation are presented in order to indicate the locations where the high- or low- frequency noise dominates. The numerical study is focused as well on the Reynolds number effects on the flow and acoustics. Copyright
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| 9. |
- Mihaescu, Mihai, et al.
(författare)
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Numerical investigations of the acoustics of a coaxial nozzle
- 2005
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Ingår i: 43rd AIAA Aerospace Sciences Meeting and Exhibit - Meeting Papers. - : AIAA. - 9781563477577 ; , s. 12601-12610
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Konferensbidrag (refereegranskat)abstract
- The acoustic field generated by two coaxial jets is studied numerically. The turbulent non-isothermal flow is handled by Large Eddy Simulations (LES) and the acoustical perturbations are treated by solving an inhomogeneous wave equation. The acoustical source is obtained from the instantaneous LES flow field. The computed flow and acoustical fields are compared to measured data. Good agreement between the computed and the measured results has been found.
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| 10. |
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