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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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于河道弯折处设置丁坝后,其水流特征显著改变,为探究该问题,采用RNG k-ε湍流模型及VOF模型对60°弯道内的单丁坝绕流进行了三维数值模拟,模拟中分别计算了设置3种丁坝的工况(模型单丁坝的长度分别为0. 15、0. 25、0. 35m)。基于数值计算的结果,重点对弯道流场结构、断面流速分布、湍流特征参数和液面特性等进行了分析探讨。研究表明:水流流经无丁坝的弯道,会对凹岸产生冲刷,凸岸造成淤积;丁坝的布设,加剧了凹、凸两岸的流速不均匀性,削弱了对凹岸的冲刷,调整了水面横比降;当丁坝长度增长,混流区的尺度变大,流体湍动能以及湍流黏度的强度和作用范围随之变大;在坝后流动分离区域,湍动能呈现最大值,在坝后旋涡中心区域,湍流黏度呈现最大值。 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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子格(SGS)模型在内流湍流中的大涡模拟 总被引:1,自引:0,他引:1
苏铭德 《水动力学研究与进展(A辑)》1994,(6):680-688
本文将子格模型应用于大涡模拟,对直方管,弯方管和弯曲槽道内充分展湍流,进行了数值模拟,并将所得的结果与实验数据作比较,计算表明,应用于子格模型的大涡模拟可以用来模拟比较复杂的内流,研究湍流运动的结构,检验湍流模型。 相似文献
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弯曲型主渠交汇是天然河流的主要交汇形式,对河床演变和水运发展产生重要影响,为了研究弯曲型交汇河口的水力特性,首先通过实验值与模拟值进行对比进行模型验证,然后通过三维数值模拟研究了流量比为0.250、0.417、0.750时,支渠分别交汇于120°弯曲主渠弯顶凹岸和凸岸的交汇口附近的水流特性,从而为进一步研究弯曲型交汇河口的动床水流创造条件。通过研究表明:相同流量比的情况下,凸岸交汇时,分离区大,凹岸交汇时,分离区小;流量比越小,上游雍水越高,交汇口下游最低水位越低;相同流量比,凸岸交汇时上游雍水大于凹岸交汇,下游最低水位低于凹岸交汇,上下游水位差更大。 相似文献
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本文利用边界层理论对二维曲壁扩压流道内部的气流流动规律进行了初步的研究。主流流场的计算采用了时间推进有限面积元方法,然后用BOX差分格式对边界层方程进行数值求解,并且在紊流切应力模式中考虑了壁面曲率的影响,由此得到流道两壁上边界层流动沿流动方向上的发展规律,最后通过三个不同来流条件的实验测量,对理论计算和分析进行了验证。结果表明:沿凸壁面的边界层流动与沿凹壁面的边界层流动具有不同的发展规律,凸壁面上的压力分布比四壁面情况下要平缓些,最大压力梯度出现得也更迟,此外,凸壁画上的壁面局部阻力系数也比相应的凹壁面为低,这说明了凸壁面上的边界层流动比较稳定。对于壁面曲率比较大的弯曲流道来说,在边界层的计算中应考虑到曲率的影响。 相似文献
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光滑及粗糙明槽湍流流动大涡模拟 总被引:2,自引:0,他引:2
采用大涡模拟(Large Eddy Simulation)方法和Smagorinsky亚格子模型数值计算了光滑及粗糙明槽湍流运动。以槽高为参考长度的雷诺数分别为3000,22800和10^5,数值离散方法为有限体积法,自由面的处理使用了简单了刚盖假定,固壁面采用了壁函数,与低雷诺数直接模拟(Direct Simulattion)和物理实验结果相比,本文数模呈现了良好的预测效果,估计的湍流宏尺度(M 相似文献
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该文发展了高阶精度有限差分格式的直接数值模拟方法,并将其成功地应用于带有自由面的热分层槽道湍流问题的计算,与低阶精度格式相比,高精度格式有着更宽的低耗散波段,对中高波数分量有较好的模拟能力。该文直接在非均匀网格上采用Lagrange多项式插值构造迎风偏置格式,克服了传统二阶格式在网格变化剧烈时精度损失的缺点,提高了在近壁区的计算精度。对三维槽道湍流以及带有自由面的热分层湍流的流场和温度场的统计特征、脉动特征以及能谱进行了分析,进一步验证了高精度差分方法对热分层剪切湍流问题直接模拟的有效性。总体上讲,该格式精度高,对高频非物理振荡有抑制作用,可以适应变化的空间网格,有效地模拟复杂湍流流动结构,并正确地揭示其流动机理. 相似文献
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槽道湍流空间变化的展向Lorentz力可以有效干扰湍流拟序结构,抑制壁湍流的产生,达到良好的减阻效果。该文以槽道流形成的充分发展的湍流边界层为基本研究对象,利用Fourier-Chebyshev谱方法,通过直接数值模拟(DNS),对槽道湍流空间变化的展向Lorentz力控制和减阻问题进行了研究。传统方法往往直接对湍流进行研究,但由于湍流结构的复杂性,减阻机理不能完全解释清楚。为解决上述问题,提出了Lorentz力对湍流的控制过程实质上是诱导流场与固有流场相互作用。首先分析了诱导流场展向速度分布特点,然后介绍了固有流场典型特征,进而把调制流场和诱导流场、固有流场进行对比,发现调制流场是通过诱导流场与固有流场相互作用实现的。研究结果表明,在优化参数控制下,诱导流场逐渐主宰壁面边界层,这导致了壁面阻力的下降,平均减阻率最高可达39%。 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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Samples were taken year-round at eleven sites along the altitudinal profile (2900-1400 m a.s.l.) of the Gunnison River, a 329 km tributary of the Colorado River, to document the distribution of the Plecoptera and to evaluate responses to hypolimnial-release dams in the headwaters and middle reaches. Twenty-two species were present, with the greatest species richness occurring in an unregulated segment upstream of the middle reach dams; average nymphal biomass over the study period (175 organisms, 395 mg dry mass m?2) was also greatest in this segment. Only four species (58 organisms, 48 mg m?2) were present in the tailwaters of the headwater dam and values were greatly reduced (nine species; 35 organisms, 180 mg m?2) below the middle reach dams. The stonefly community recovered ca. 80 km downstream from the last dam (15 species; 244 organisms, 250 mg m?2), apparently in response to natural resetting of environmental conditions corresponding to those above the middle reach dams. At the most downstream site (11) only four species (four organisms, 16 mg m?2) were present. The observed distributional pattern is a classic serial discontinuity in response to hypolimnial stream regulation in a temperate latitude river. 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