| 1. |
- Ghulam, M. M., et al.
(author)
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Characterization of Non-reacting Swirling Flow in a Gas Turbine Fuel Injector
- 2021
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In: AIAA Scitech 2021 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA). ; , s. 1-22
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Conference paper (peer-reviewed)abstract
- The current work investigates the swirling flow of a gas fuel injector utilized in the Lean Direct Injection (LDI) combustion system. Planer particle image velocimetry (PIV) measurements and large eddy simulation (LES) numerical analysis are conducted to have a profound understanding of the swirling flow characteristics. Specifically, the impacts of the level of confinement with a rectangular cross-section and different Reynolds number are examined. Increasing the Reynolds number increases the strength of swirling jets and reverse flow region. More significant changes occurred on the mean flowfield due to the confinement effect such as increasing the width of the reverse flow region and increasing/decreasing the size of the recirculation zones which in turn effects the inlet jet penetration. The inlet jet spreads at a larger angle as the size of the outer recirculation zone (ORZ) increases with the confinement ratio. The shape of the inner recirculation zone (IRZ) vortex structure on the unconfined flow is characterized to be a thin and short vortex and located on top of the nozzle exit, and it becomes thicker and longer vortex located further downstream from the nozzle exit upon confinement. The increased size of the IRZ vortex structure in confined cases is an indication of the increased thickness of the inner shear layer (ISL) that increases linearly as the confinement ratio increases. LES results reveled there is a connection channel between the reverse flow region and the ORZ of the swirling flow emanating from the multiple-jet LDI nozzle. Higher level of turbulence is associated with the location of the IRZ vortex structure. Proper orthogonal decomposition (POD) analysis is preformed to extract coherent fluctuating flow features. The swirling flow of the LDI nozzle exhibits the single-helical and double-helical precessing vortex core (PVC) modes, with the first one being the most energetic mode. The general flow structure of the coherent single-helix PVC mode on the unconfined flow consists of four vortices: two corner vortices rotating in opposite of each other, and a tiny vortex on top of the nozzle exit followed by a huge central vortex rotating in a different direction. Upon confinement the outer vortices attached to the wall of the combustor and the central vortex becomes about twice bigger. The preexistence of the outer vortices on the unconfined flow suggests that the formation of the ORZ is not caused by the confinement, but rather it is a part of the natural behavior of a highly turbulent swirling flow which magnified in the case of confined environment. The single-helix PVC mode gains higher energy value and becomes less-sensitive to the increase of the Reynolds number as the confinement ratio decreases. This is linked to the asymmetry mode shapes, and energy content linearity between the axial and radial components associated with the single-helix PVC mode.
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| 2. |
- Szasz, R., et al.
(author)
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Hysteretic Dynamics of Flashback in a Low-Swirl Stabilized Combustor
- 2017
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In: Combustion Science and Technology. - : Taylor & Francis. - 0010-2202 .- 1563-521X. ; 189:2, s. 266-289
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Journal article (peer-reviewed)abstract
- The hysteretic behavior of flashback (FB) and flash forward (FF) in methane and natural gas flames, stabilized by a low swirl fuel injector, is investigated using high speed OH* chemiluminescence and particle image velocimetry. Due to the lack of vortex breakdown, the two mechanisms discussed are boundary layer and turbulence induced FB. Two hysteresis cycles were identified, one when FB is induced by increasing the equivalence ratio starting from lean conditions, and the other by decreasing the equivalence ratio starting from rich conditions. Impact of relevant parameters including Reynolds number (Re), equivalence ratio, fuel type, combustion chamber geometry, preheating, and mixing tube protrusions are investigated. As Re is increased, the equivalence ratio at which both rich and lean flashbacks occur approaches stoichiometric conditions. However, the range of the hysteresis cycle between FB and FF is independent on Re. The transition processes during FB and FF are quite variable and their duration is independent on Re. The mean duration of FB transition initiated from lean conditions is nearly twice longer than the rich branch and also longer than both the lean and rich FF. The geometry of the combustion chamber affected neither FB nor FF. However, preheating increased the equivalence ratio at which FB occurred but did not affect FF. Also, FB had significant effect on the mean flow field.
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| 3. |
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| 4. |
- Guillou, E., et al.
(author)
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Surge characteristics in a ported shroud compressor using PIV measurements and large eddy simulation
- 2010
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In: 9th International Conference on Turbochargers and Turbocharging - Institution of Mechanical Engineers, Combustion Engines and Fuels Group. ; , s. 161-170
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Conference paper (peer-reviewed)abstract
- Compressors operating range is limited at low mass flow by the development of surge. The objective of this research is to study effective operational range for a turbocharger ported shroud compressor typically used in diesel engines. Surge characteristics are assessed by planar flow measurements in the vicinity of the compressor inlet along with numerical computations in the entire compressor geometry. In this paper, satisfying characterization of the compressor instabilities was achieved. Experimental measurements yielded a better understanding of the flow interactions occurring at the compressor entrance and the validation of the computational results in stable regime for this specific model.
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| 5. |
- Hafsteinsson, Haukur, 1984, et al.
(author)
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Noise Control of Supersonic Jet with Steady and Flapping Fluidic Injection
- 2015
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In: AIAA Journal. - 1533-385X .- 0001-1452. ; 53:11, s. 3251-3272
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Journal article (peer-reviewed)abstract
- Large-eddy simulation is used to investigate steady-state mass flow injection into a supersonic jet stream with and without flapping motion of the microjets. The results are validated with particle image velocimetry and acoustic measurements. The effect of microjet penetration on the far-field acoustics is studied by altering the number of injectors, the cross-sectional area of each injector, and the injection mass flow. The injectors are evenly distributed around the nozzle exit. The injection angle is 90 deg relative to the main jet flow. This research is a continuation of a previous large-eddy simulation study of pulsed injection that showed that the unsteady injection-induced pressure pulses in the jet caused increased tonal noise for far-field observers at low angles. Flapping jet injection was shown to minimize the creation of the pressure pulses, except for high-amplitude flapping angles and high injection mass flows, where the injections divert out of the shear layer and introduce periodic superposition of the double shock-cell structure. Furthermore, the flapping injection did not show improved noise reduction compared with the steady injection, which is essentially promising because steady injection proves to be a more practical solution for implementation in real jet engine applications.
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| 6. |
- Hellström, F., et al.
(author)
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Stall development in a ported shroud compressor using PIV measurements and Large Eddy Simulation
- 2010
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In: SAE Technical Papers. - 400 Commonwealth Drive, Warrendale, PA, United States : SAE International.
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Conference paper (peer-reviewed)abstract
- Surge is a phenomenon that limits the operational range of the compressor at low mass flow rates. The objective of this research is to study effective operational range for a ported shroud compressor. The size of the compressor is typical for a turbocharger used on diesel engines. To be able to extend the operational range, the surge characteristics have to be assessed. This is done by performing measurement of the flow at the inlet to the compressor wheel and pressure fluctuations at the inlet and outlet of the compressor housing. Detailed numerical computations of the flow in the entire compressor section under similar operating conditions have also been carried out. The experimental work includes Particle Imaging Velocimetry (PIV) measurements of the instantaneous and mean velocity field at the inlet. At surge, low frequency pulsations are detected that seem to result from back flow already observed in stall. The numerical computations include details of the flow by having good spatial and temporal resolution and using Large Eddy Simulations (LES) to account for the turbulence. LES is most suitable for the surge flow since it resolves the large scale structures, such as flow separation and reversed flow, which characterize surge.
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| 7. |
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| 8. |
- Yellugari, K., et al.
(author)
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Effect of nozzle spacing on flow behavior in a lean direct injection combustor
- 2021
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In: AIAA Scitech 2021 Forum. - Reston, Virginia : American Institute of Aeronautics and Astronautics (AIAA). ; , s. 1-13
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Conference paper (peer-reviewed)abstract
- A numerical study has been performed on a linear array of five nozzles in a lean direct injection (LDI) combustor for three mass flow rates and four different inter-nozzle spacings, using two equation realizable k − ɛ turbulence model. It is observed that the mass flow rates do not affect the flow patterns in this five nozzle configuration. The two smaller inter-nozzle spacings, s = 1.25d and 1.5d, developed asymmetric flow patterns. Especially at 1.5d, the asymmetry is quite dominant in the core flows of nozzles N2 and N4, due to the non-merging of jets in the shear layers. But, at higher nozzle spacings, s = 1.75d and 2d, the jets merge in the shear layers and move downstream as a single jet. Due to the slower expansion of the flow in the radial direction, strong and compact central toroidal recirculation zones (CTRZ) are formed at smaller inter-nozzle spacings, 1.25d and 1.5d. These compact CTRZs contribute to higher turbulence kinetic energy (TKE) in regions between the nozzles and closer to the dome-plate. These regions correspond to higher velocity and higher shear stress in the flow. As the inter-nozzle spacing is increased, the intensity of TKE decreases between the nozzles.
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