青藏高原乡村人群对气候变化影响的感知与适应

青藏高原是全球气候变化的敏感区和脆弱区。研究青藏高原乡村人群对气候变化的感知与适应状况,对提高乡村人群气候变化的适应能力,促进青藏高原地区的社会稳定和可持续发展意义重大。本文采用问卷调查和访谈相结合的方式,分析了青藏高原乡村人群对气候变化感知与适应的现状。结果表明:在气候变化对农牧业的影响感知方面,68%的调查对象认为草场返青时间提前,62%认为在气候变化后草场状况恶化,78%认为农作物播种时间提前。在气候变化带来的不利影响感知方面,调查对象最担心的 3 个问题依次是:干旱更加严重(50.4%)、水资源矛盾突出(48.5%)、农业粮食安全(36.8%)。对气候变化的适应对策主要是:完善水利设施,采用高效节水灌溉技术(73.8%)、增加塑料地膜覆盖面或作物秸秆覆盖(58.2%)、调整农作物种植结构,改变作物布局(47.6%)。

Characteristics of penetration and distribution of a liquid jet in a divergent cavity-based combustor

The atomization process of a liquid jet in a divergent cavity-based combustor was investigated experimentally using high-speed photography and schlieren techniques under a Mach number 2.0 supersonic crossflow.Gas-liquid flow field was studied at different divergent angles and injection schemes.It is found that complex wave structures exist in the divergent cavity-based combustor.The spray field can be divided into three distinct zones:surface wave-dominated breakup zone,rapid atomization zone and cavity mixing zone.A dimensionless spray factor is defined to describe the concentration of spray inside the cavity qualitatively.As a result,it is revealed that for the large divergent angle cavity,the injection scheme near the upstream inlet has a higher penetration depth but a lower spray distribution,where the injection scheme near the cavity has a more spray distribution.For the small divergent angle cavity,the injection scheme near the upstream inlet also has a higher penetration depth and the injection scheme near the start point of the divergent section has a more sufficient spray distribution.The small divergent angle cavity-based combustor with the upstream wall transverse injection is an optimized injection scheme to improve both penetration and spray distribution inside the cavity.Finally,a penetration depth formula is proposed to explain the spray and distribution behaviors in the divergent cavity-based combustor.

Review of atomization mechanism and spray characteristics of a liquid jet in supersonic crossflow

The injection and atomization process of a liquid fuel jet is critical for an ignition start of a scramjet engine.Airwall-mounted crossflow injection strategy is widely used in scramjet combustors,avoiding high total pressure loss and allowing the liquid fuel to rapidly undergo atomization,mixing,and evaporation.In this review,research progress on a liquid jet in supersonic crossflow was evaluated from aspects of atomization mechanism and spray characteristics.When a liquid jet is injected into a supersonic crossflow,primary and secondary breakups occur successively.The surface instability of liquid can significantly affect the breakup process.This review discusses the current understanding of the breakup process and spray characteristics of a liquid jet in supersonic crossflow including the mechanism of atomization and the characteristics of distribution and atomization.The development of windward Rayleigh-Taylor(R-T)unstable waves is the main factor in column breakup.The development of Kelvin-Helmholtz(K-H)unstable waves along the circumferential direction of the jet or droplets is the main factor of surface and droplet breakups.The liquid-gas momentum ratio is the most important factor affecting the penetration depth.The span width of the liquid jet is affected by the windward area.Breakup and coalescence lead to a transformation of the size distribution of droplets from S-or C-shaped to I-shaped,and the velocity distribution of the droplets on the central symmetry plane has a mirrored S-shape.The droplet distribution on the spanwise cross-section retains a structure similar to an“Ω”shape.At last,some promising recommendations have been proposed,namely a theoretical predictive model which can describe the breakup mechanism of a liquid jet,the distribution characteristics and droplets size distribution of a liquid jet under a cavity combustion chamber,especially for enthalpy flows with complex wave structures.