A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined j...A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala展开更多
Traditional rural social-ecological systems(SES)share many features which are crucial for sus-tainable development.Eastern European countries such as Romania,are still rich in traditional cultural landscapes.However,t...Traditional rural social-ecological systems(SES)share many features which are crucial for sus-tainable development.Eastern European countries such as Romania,are still rich in traditional cultural landscapes.However,these landscapes are increasingly under internal(e.g.,people’s aspirations toward western socioeconomic ideals)and external(institutional changes,globalization of the commodity market,connectivity with other cultures)pressures.Therefore,understanding the ways how traditional SES navi-gated past and more recent changes is of crucial importance in getting insights about the future trajectory of these systems.Here,we present the rural SES from the Saxon region of Transylvania through the lens of institutional transitions which happened in the past century in this region.We show that the rural SES went through episodic collapses and renewals,their cyclic dynamic being related to the episodic chang-es of the higher level formal institutions.These episodic collapses and renewals created a social-ecolog-ical momentum for the sustainability of these SES.While we recognize that policy effectiveness depends on institutional stability(and institutions are unstable and prone to collapses),maintaining those social-ecological system properties which can assure navigation of societies through the challenges imposed by global changes should be in the heart of every governance system.Such properties includes wide extent of native vegetation,fertile soils,wide range of provisioning ecosystem services,genuine links between people and landscapes and knowledge about the social-ecological systems.These features could provide important capitals and memory elements for the(re)emergence of social-ecological systems(old or new).展开更多
文摘A comprehensive numerical study on the three-dimensional structure of a turbulent jet in crossflow is performed. The jet-to-crossflow velocity ratio (R) varies in the range of 2 - 16; both vertical jets and inclined jets without excess streamwise momentum are considered. The numerical results of the Standard two-equation k-ε model show that the turbulent structure can be broadly categorised according to the jet-to-crossflow velocity ratio. For strong to moderate jet discharges, i.e. R> 4, the jet is characterized by a longitudinal transition through a bent-over phase during which the jet becomes almost parallel with the main freestream, to a sectional vortex-pair flow with double concentration maxima; the computed flow details and scalar mixing characteristics can be described by self-similar relations beyond a dimensionless distance of around 20-60. The similarity coefficients are only weakly dependent on R. The cross-section scalar field is kidney-shaped and bifurcated, vvith distinct double concentration maxima; the aspect ratio is found to be around 1.2. A loss in vertical momentum is ob-served and the added mass coefficient of the jet motion is found to be approximately 1. On the other hand, for weak jets in strong crossflow, i. e. R ≥ 2, the lee of the jet is characterized by a negative pressure region. Although the double vortex flow can stili be noted, the scalar field becomes more symmetrical and no longer bifurcated. The similarity coeffcients are al-so noticeably different. The predicted jet flovv characteristics and mixing rates are well supported by experimental and field dala
基金The publication of this manuscript was supported by the EEA Financial Mechanism and the Romanian Ministry of Environment,Forests and Waters under the project“Mapping and assessment of ecosystem services in Natura 2000 sites of the Niraj-Tarnava Mica region”(Programme RO02,grant No.3458/19.05.2015 to Milvus Group)through Bálint Czúcz.BC was supported also by the Bolyai scholarship of the Hungarian Academy of Sciences.
文摘Traditional rural social-ecological systems(SES)share many features which are crucial for sus-tainable development.Eastern European countries such as Romania,are still rich in traditional cultural landscapes.However,these landscapes are increasingly under internal(e.g.,people’s aspirations toward western socioeconomic ideals)and external(institutional changes,globalization of the commodity market,connectivity with other cultures)pressures.Therefore,understanding the ways how traditional SES navi-gated past and more recent changes is of crucial importance in getting insights about the future trajectory of these systems.Here,we present the rural SES from the Saxon region of Transylvania through the lens of institutional transitions which happened in the past century in this region.We show that the rural SES went through episodic collapses and renewals,their cyclic dynamic being related to the episodic chang-es of the higher level formal institutions.These episodic collapses and renewals created a social-ecolog-ical momentum for the sustainability of these SES.While we recognize that policy effectiveness depends on institutional stability(and institutions are unstable and prone to collapses),maintaining those social-ecological system properties which can assure navigation of societies through the challenges imposed by global changes should be in the heart of every governance system.Such properties includes wide extent of native vegetation,fertile soils,wide range of provisioning ecosystem services,genuine links between people and landscapes and knowledge about the social-ecological systems.These features could provide important capitals and memory elements for the(re)emergence of social-ecological systems(old or new).
