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991.
Evaluation of CFD Simulation using RANS Turbulence Models for Building Effects on Pollutant Dispersion 总被引:5,自引:0,他引:5
CFD evaluations were performed to examine the applicability of the RANS methods in simulating pollutant dispersion near, within
and over three typical building configurations: (1) an isolated building, (2) a building array and (3) an urban intersection.
The CFD results are compared with values obtained from wind tunnel tests. In some situations major differences between the
wind tunnel tests and the CFD results were observed. The main source of difference between the CFD and wind tunnel results
was inadequate modelling of local flow patterns using the RANS turbulence models. Also inappropriate evaluation of high intermittent
turbulent mixing in the RANS approach may lead to either over-prediction or under-prediction of the concentration level, by
up to a factor of 10, depending on the case investigated. 相似文献
992.
993.
梁红叶 《辽宁城乡环境科技》2007,27(1):15-16
根据煤堆起尘量经验公式,结合区域面源污染研究工作,提出煤场扬尘的主要影响因素,从而对煤场扬尘在区域大气面源污染中的重要性进行具体分析,并提出治理措施。 相似文献
994.
我省自八十年代初始,已开展了生态农业试点建设,在不同区域条件下取得了明显的经济、生态、社会三大效益。“八五”期间试点范围还将会扩大,在此基础上,提出评价指标为生态农业建设规范化提供依据。本文拟写评价指标体系及其标准原则、评价方法、指标体系的解释和评价单项指标群体。通过指标评价方法,既可找出影响生态经济功能的限制因子,又可找到问题的突破口及配套措施。将有效地促进县级生态农业的健康发展。 相似文献
995.
996.
R. Thomas James Karl E. Havens 《Journal of the American Water Resources Association》1996,32(5):995-1006
ABSTRACT: Algal blooms, defined as chlorophyll α concentrations greater than 40 μg l?1, are common in Lake Okeechobee, Florida. Using logistic regression techniques, we have developed equations that relate limnological variables to algal bloom occurrence in four distinct open-water regions of this large shallow lake: central pelagic, northwest, southwest, and a transition region between the western and pelagic regions. Wind velocity and total phosphorus, which are closely related to resuspended material in the central region, are negatively related to algal bloom occurrence there. In the transition region, algal bloom occurrence is positively related to total nitrogen and wind velocity. Algal bloom occurrence is strongly and positively related to total nitrogen and total phosphorus concentrations in the western regions. The logistic regression model predicts an algal bloom probability greater than 95 percent in the northwest region when total phosphorus exceeds 0.10 mg l?1 and total nitrogen exceeds 2.5 mg l?1. In the southwest region the model predicts algal bloom probability of 100 percent when total phosphorus exceeds 0.10 mg l?1 and total nitrogen exceeds 2.8 mg l?1. Given 1994 mean total phosphorus concentrations of 0.05 and 0.04 mg l?1 in the northwest and southwest regions, respectively, total nitrogen would have to remain below 1.32 and 1.43 mg l?1, respectively, to keep the algal bloom probability below 10 percent. Because the lake is heterogenous, such nutrient standards should be considered on an in-lake regional basis for Lake Okeechobee. 相似文献
997.
Kimio Sato 《Journal of Loss Prevention in the Process Industries》1989,2(4):209-214
Steam curtain equipment is used to prevent leaking flammable gases from reaching ignition sources, such as furnaces. However, steam curtains are sometimes designed badly and are ineffective for preventing the leaking gas from spreading in the windward direction. The leaked gas may pass on either side of the stream curtain, it may pass between the nozzles, or it may pass on the upper side of the stream curtain. At present, data to design the best stream curtains are quite rare. It is necessary to obtain fundamental data on the entrainment of air by steam jet and on the inclination of the steam curtain caused by the strong wind. Therefore, a series of experiments to investigate the entrained air and the inclination of the steam curtain were performed, in addition to further theoretical considerations. Thus, fundamental data useful for the design of the steam curtain equipment have been obtained. 相似文献
998.
北京地区偏南风和偏东风条件下污染特征差异 总被引:5,自引:5,他引:0
为探究污染的控制风向特征差异及其长期演变趋势,对2014~2019年北京地区逐小时气象要素和PM2.5浓度统计分析.结果表明,研究时段内北京地区67%的污染发生在偏南风和偏东风的控制下,且冬季最易出现污染,其次为春季和秋季,各自对应的冬、春、秋和夏季平均污染概率为45.2%、34.1%、32.1%和26.1%及47.0%、45.8%、39.7%和29.6%.北京偏南风频率更高,但偏东风下污染概率更大,污染差异在春季最明显11.7%(2.8%~18.6%),冬季最小1.8%(-7.6%~13.9%).过去6 a,偏南风和偏东风下的污染概率分别以每年4.6%~8.0%和5.5%~7.9%的速度降低,很大程度体现在中度及以上程度污染占比的减少.偏南风下污染发生时,能见度和混合层高度偏高、风速偏大、小时风速≥3 m ·s-1的时次偏多、相对湿度和露点温度偏低,春季、夏季和秋季的PM2.5平均、峰值和75%百分位浓度显著低于偏东风控制下的污染,而冬季PM2.5浓度则偏高.这表明,污染发生时,偏南风下大气对污染物的承载和扩散能力略好于偏东风,且偏东风下大气含水量的增加有利于污染的维持和加重.而冬季,原有排放加上城市供暖的影响,偏南风输送的污染气团可能更有助于PM2.5浓度的升高.此外,春季、夏季和秋季的污染逐渐向"偏东风型"发展,但冬季一直保持"偏南风型"污染. 相似文献
999.
Charles G. Hanlon R. L. Miller B. F. McPherson 《Journal of the American Water Resources Association》1998,34(4):951-961
ABSTRACT: Relationships between wind velocity and the vertical light attenuation coefficient (K0) were determined at two locations in a large, shallow lake (Lake Okeechobee, Florida, USA). K0 was significantly correlated with antecedent wind conditions, which explained as much as 90 percent of the daily variation in K0. Sub-surface irradiance began to change within 60 to 90 minutes of the time when wind velocity exceeded or dropped below a threshold value. Maximum one hour changes in K0 were > 50 percent, however, 20 to 30 percent changes were more common. The magnitude of change in K0 varied spatially based on differences in sediment type. K0 never exceeded 2.8 at a location where bottom sediments were dominated by a mixture of coarse sand and shells. In comparison, K0 exceeded 9 during episodic wind events where the bottom sediment was comprised of fine grain mud. Underwater irradiance data can be used to determine threshold wind velocity and account for the influence sediment type has on K0. Once a threshold velocity has been established, the frequency, rate, and duration of expected change in underwater irradiance can be evaluated. This is critical information for scientists who are studying algal productivity or other light-related phenomena. 相似文献
1000.