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对一台双吸离心泵的能量特性和空化外特性进行了试验测量,基于SST k-ω湍流模型及Zwart-GerberBelamri空化模型对双吸离心泵内部流动进行数值模拟,计算得到的双吸离心泵扬程曲线、效率曲线及扬程随有效空化余量变化曲线与试验结果吻合较好。数值模拟结果表明:随着有效空化余量的减小,叶轮内低压区从叶轮进口处向出口处渐渐扩大,叶轮内空化沿叶片吸力面从叶片头部向叶片尾部逐渐发展,并集聚在叶片吸力面顶部附近;泵扬程下降的主要原因是叶轮内空泡的阻塞作用,并叶轮内空化发展到一定程度时叶轮流道内出现旋涡区,使影响叶轮内部流态,导致泵扬程突降。 相似文献
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展向周期振动的平板近壁湍流结构研究 总被引:1,自引:0,他引:1
通过直接数值模拟(DNS)对壁面作展向周期运动的槽道湍流进行研究,建立了槽道湍流数据库.通过改变振幅大小和振动周期,可以使壁面阻力明显减少.根据计算结果分析了减阻率和振动参数的关系.利用减阻后近壁湍流拟序结构的变化,研究了壁面展向周期振动减阻的内在机理,揭示了三种减阻过程中涡结构对近壁流体的上抛、下扫运动以及条带结构的影响规律. 相似文献
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液流中边壁附近的空泡溃灭研究 总被引:1,自引:0,他引:1
本文利用高速摄影方法观测了液流中的空泡溃灭过程,分析了空泡在流动系统中溃灭时的泡壁稳定性,和由于空泡射流挟带其表面分裂出的微小泡冲击边壁,从而使微小泡在高压强作用下溃灭,造成壁面破坏的可能性。本文还研究了液体粘性变化和液体挟带颗粒对空泡微射流速度及溃灭历时的影响 相似文献
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在全面考虑壁面对空泡运动粘悸阻力和升力影响的基础上,建立了空泡在近壁区内的运动微分控制方程,通过频谱分析,考察了壁面的存在对空泡频率响应特性和湍强度等方面的影响,并与壁面对固体颗粒运动和影响进行了比较 。 相似文献
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为了研究边界层涡结构对沟槽壁面摩擦阻力的影响,该文利用FLUENT软件对湍流状态下沟槽壁面进行数值模拟计算,分析了90°、120°和150°三种不同张角下沟槽壁面的减阻效果,获得了不同张角的沟槽结构对减阻效果的影响规律。结果表明:沟槽内形成的旋涡结构可以有效减小沟槽布置区域法向速度梯度,减弱流层间剪切作用,增加条带结构稳定性,湍流猝发频率降低,从而使壁面摩擦阻力降低。当来流速度v=25 m/s,沟槽张角β=90°时,可取得最佳减阻效果。在沟槽结构布置区域,流向涡的涡头上扬角度变大,上扬和下扫强度减弱,有效减小了摩擦阻力;同时,沟槽结构改变近壁区速度分布,使流向涡密度减小,从而减小壁面摩擦阻力。 相似文献
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离心泵叶轮的优化设计 总被引:5,自引:0,他引:5
本文用优化方法对叶轮的结构参数进行优化,并采用载荷法设计叶片的型线。计算了叶轮内的速度分布。应用本方法对3B-33型离心泵进行了改型设计,测试并对比了泵的外特性和叶轮效率。 相似文献
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为了研究离心泵空化诱导的非定常激励特性,采用数值模拟方法,分析了泵叶轮内压力脉动、涡量脉动及径向力特性。结果表明:叶轮内压力脉动的主频均为叶轮转频fi,涡量脉动的主频为1/5fi、fi、2fi;压力脉动强度从叶轮进口到出口逐渐增强;涡量脉动强度在叶轮出口处最大,进口处其次,叶片中部最小;空化发展诱发低频压力脉动和低频涡量脉动;径向力的大小和方向,由于空泡排挤作用而发生变化,空化充分发展时空泡脱落和溃灭,导致径向力骤增。对离心泵内空化诱导的振动和噪声产生机理的深入研究提供了参考。 相似文献
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根据冗各电站地下厂房开挖支护的施工顺序,以隐式杆单元模拟锚杆,以壳单元模拟混凝土喷层,采用三维非线性有限元技术,对洞室群的开挖支护动态过程进行了模拟计算。通过三维非线性有限元计算分析得到:洞室群动态开挖过程中围岩应力变形的分布规律,围岩塑性区的发展规律,锚杆受力变化情况。计算结果表明:整个开挖过程中,洞周围岩位移变化规律正常,量值较小,塑性区主要分布在洞室周边,围岩稳定性较好;但在洞室交叉口处围岩的变形较大,出现较大范围的塑性区,在此基础上提出了支护措施优化方案,并对优化方案的效果进行了评价。 相似文献
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The relocation of unionacean mussels is commonly used as a conservation and management tool in large rivers and streams. Relocation has been used to recolonize areas where mussel populations have been eliminated by prior pollution events, to remove mussels from construction zones and to re-establish populations of endangered species. More recently, relocation has been used to protect native freshwater mussels from colonization by the exotic zebra mussel Dreissena polymorpha. We conducted a literature review of mussel relocations and evaluated their relative success as a conservation and management strategy. We found that 43% of all relocations were conducted because of construction projects that were forced to comply with the Endangered Species Act 1973 and that only 16% were monitored for five or more consecutive years. Most (43%) relocation projects were conducted from July to September, presumably a period when reproductive stress is relatively low for most species and the metabolic rate is sufficient for reburrowing in the substrate. The mortality of relocated mussels was unreported in 27% of projects; reported mortality varied widely among projects and species and was difficult to assess. The mean mortality of relocated mussels was 49% based on an average recovery rate of 43%. There is little guidance on the methods for relocation or for monitoring the subsequent long-term status of relocated mussels. Based on this evaluation, research is needed to develop criteria for selecting a suitable relocation site and to establish appropriate methods and guidelines for conducting relocation projects. 相似文献
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In the lower River Murray, Australia, populations of gastropods have declined markedly over the past 40 years. Of the native fauna of about 18 species, only the ancylid Ferrissia petterdi remains common (but in patches), and another five species feature in sporadic local resurgences. Until recently the viviparid Notopala was thought to be extinct. The introduced physid Physa acuta is widespread, but in low numbers. The decline probably is associated with flow regulation, high turbidity and the introduction of common carp. Snail populations have persisted, however, in irrigation pipelines fed from the river, where they periodically cause blockages. This paper reports the discovery of the only known populaion of Notopala hanleyi in a pipeline where the inner wall accumulates microbial and other organic matter, providing high quality food for snails. In the Murray before regulation most of the periphytic biomass was probably microbial, as fluctuating water levels would have maintained littoral communities in a highly productive, early state of succession his postulated that, by stabilizing seasonal water levels, regulation has promoted the production of filamentous green algae, an inferior food source, and so displaced snail populations from the open aquatic environment. 相似文献
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V. K. Konovalov O. V. Yashkin V. V. Ermakov 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2008,42(2):105-109
A system for removal and pneumatic transport of fly ash is examined, in which air pulses act on batches (pistons) of ash formed
in a duct. Studies are made of the effect of several physical parameters on the force required to displace a piston of ash
and these serve as a basis for choosing a system for removal and pneumatic transport of ash simultaneously from several hoppers
of an electric precipitator. This makes it possible to separate the ash particles according to size without introducing additional
components. Formulas are given for calculating the structural and dynamic parameters of this system and measurements of indirect
dynamic parameters are used to calculate the input-output characteristics of the system. In order to optimize the system,
configurations for summing several ducts into a single transport duct for pneumatic ash transport are proposed. Some variants
of dry ash utilization and the advantages of producing of size-separated particles are considered.
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Translated from élektricheskie Stantsii, No. 2, pp. 26–30 (2008). 相似文献
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Peter B. Bayley 《河流研究与利用》1991,6(2):75-86
The ‘flood pulse advantage’ is the amount by which fish yield per unit mean water area is increased by a natural, predictable flood pulse. Evidence for this increase is presented from tropical and temperate fisheries. It is argued that increasing multispecies fish yield by restoring the natural hydrological regime is consistent with increasing production of other trophic levels and with restoration from ecological and aesthetic viewpoints. When applied to a river-floodplain system, this restoration would provide a large, self-sustaining potential for recreation, commercial exploitation, and flood control. An interim ‘natural flood pulse’ restoration approach is proposed for systems modified for navigation. This approach approximates the natural hydrological regime in a river reach and is intended as a first step in the long process of restoring the watershed. 相似文献
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简述天湖水电站投运以来各种故障的表现形式,分析其原因,提出了相应的处理方法及措施,并对合理利用国内外设备提出建议。 相似文献