| 1. |
- Guo, Shilong, et al.
(författare)
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Investigation on bluff-body and swirl stabilized flames near lean blowoff with PIV/PLIF measurements and LES modelling
- 2019
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- Lean premixed combustion (LPC) is a promising technology for low-NOx emission, while it increases the risk of blowoff at the same time. Experiments and Large Eddy Simulations (LES) on swirl stratified lean-premixed CH4/air flames were performed to study the differences between the stable and near blowoff flame. The flow fields and instantaneous flame structures were measured by simultaneous Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (OH-PLIF). The Thickened Flame (TF) model coupled with a two-step reduced chemical mechanism was used in LES modelling. The non-dynamic formulation of sub-grid flame wrinkling model is performed well for stable condition while it cannot predict the near lean blowoff flame reasonable. Compared with the stable flame, several significant differences can be observed in the near lean blowoff flame. The height of high-temperature-zone is relatively low and the heat loss of flame attachment can be easily enhanced by the low temperature spot induced by flame-vortex interaction. The flame attachment is subject to higher excess strain rate and turbulence fluctuation. Meanwhile, a Processing Vortex Core (PVC) appears downstream of the centerline. It is concluded that lean blowoff is the result of interactions between the fuel/air mixture ignition, PVC instability and flame attachment lift-off.
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| 2. |
- Guo, Shilong, et al.
(författare)
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Numerical simulation of premixed combustion using the modified dynamic thickened flame model coupled with multi-step reaction mechanism
- 2018
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 233, s. 346-353
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Tidskriftsartikel (refereegranskat)abstract
- Thickened flame (TF) model is one of the effective methods to resolve the flame front in turbulent premixed combustion modeling. The multi-step reaction mechanism is becoming increasingly important for combustion simulations such as pollutant formation, ignition and extinction. The effect of TF model on flame structures when coupling with multi-step reaction mechanism was investigated. The simulation results show that, no matter in laminar or turbulent condition, the global TF model coupling with multi-step reaction mechanism results in an incomplete combustion, which is mainly due to the enhanced species diffusion. Although Durand and Polifke's dynamic thickened flame (DTF) sensor performs well for predicting laminar flame structure when coupling with multi-step reaction mechanism, it underestimates the effective thickening factor. In turbulent premixed flame simulation, the underestimated thickening factor leads to a faster local fuel consumption speed because of the over-predicted sub-grid flame wrinkling factor. A modified DTF sensor suitable for multi-step reaction mechanism is proposed. This sensor using the hyperbolic tangent function of progress variable to calculate thickening factor dynamically. It ensures that both the preheated and reaction zones are thickened effectively. The sub-grid wrinkling factor is hence estimated corresponding to the calculated flame thickness. Results of 1D laminar and 3D turbulent flame show that this method performs well for predicting both burned gas temperature and species concentration in burnt gas, which is important for predicting emissions.
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| 3. |
- He, Bin, et al.
(författare)
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Worldwide impacts of atmospheric vapor pressure deficit on the interannual variability of terrestrial carbon sinks
- 2022
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Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 9:4
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Tidskriftsartikel (refereegranskat)abstract
- Interannual variability of the terrestrial ecosystem carbon sink is substantially regulated by various environmental variables and highly dominates the interannual variation of atmospheric carbon dioxide (CO2) concentrations. Thus, it is necessary to determine dominating factors affecting the interannual variability of the carbon sink to improve our capability of predicting future terrestrial carbon sinks. Using global datasets derived from machine-learning methods and process-based ecosystem models, this study reveals that the interannual variability of the atmospheric vapor pressure deficit (VPD) was significantly negatively correlated with net ecosystem production (NEP) and substantially impacted the interannual variability of the atmospheric CO2 growth rate (CGR). Further analyses found widespread constraints of VPD interannual variability on terrestrial gross primary production (GPP), causing VPD to impact NEP and CGR. Partial correlation analysis confirms the persistent and widespread impacts of VPD on terrestrial carbon sinks compared to other environmental variables. Current Earth system models underestimate the interannual variability in VPD and its impacts on GPP and NEP. Our results highlight the importance of VPD for terrestrial carbon sinks in assessing ecosystems' responses to future climate conditions.
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| 4. |
- Yao, Tandong, et al.
(författare)
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Recent Third Pole’s rapid warming accompanies cryospheric melt and water cycle intensification and interactions between monsoon and environment: multi-disciplinary approach with observation, modeling and analysis
- 2019
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Ingår i: Bulletin of The American Meteorological Society. - 0003-0007 .- 1520-0477. ; :March, s. 423-444
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Tidskriftsartikel (refereegranskat)abstract
- The Third Pole (TP) is experiencing rapid warming and is currently in its warmest period in the past 2,000 years. This paper reviews the latest development in multidisciplinary TP research associated with this warming. The rapid warming facilitates intense and broad glacier melt over most of the TP, although some glaciers in the northwest are advancing. By heating the atmosphere and reducing snow/ice albedo, aerosols also contribute to the glaciers melting. Glacier melt is accompanied by lake expansion and intensification of the water cycle over the TP. Precipitation has increased over the eastern and northwestern TP. Meanwhile, the TP is greening and most regions are experiencing advancing phenological trends, although over the southwest there is a spring phenological delay mainly in response to the recent decline in spring precipitation. Atmospheric and terrestrial thermal and dynamical processes over the TP affect the Asian monsoon at different scales. Recent evidence indicates substantial roles that mesoscale convective systems play in the TP’s precipitation as well as an association between soil moisture anomalies in the TP and the Indian monsoon. Moreover, an increase in geohazard events has been associated with recent environmental changes, some of which have had catastrophic consequences caused by glacial lake outbursts and landslides. Active debris flows are growing in both frequency of occurrences and spatial scale. Meanwhile, new types of disasters, such as the twin ice avalanches in Ali in 2016, are now appearing in the region. Adaptation and mitigation measures should be taken to help societies’ preparation for future environmental challenges. Some key issues for future TP studies are also discussed.
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