切线泵流动特征的整流场数值模拟

对单级切线泵在设计工况进行了定常流动数值模拟，分析了叶轮流道及蜗壳内的液体流动情况。结果表明，切线泵内流场非常复杂，叶轮进口有明显冲击，叶轮各流道的速度、压力差异很大，环形蜗壳内流动呈现旋涡推进特征，上、下游流动有强烈的相互作用，整机流场不具有对称性；环形蜗壳的几何结构以及流场上、下游的相互作用是导致整机流场非对称特性的主要原因。计算结果为进一步改进结构、提高性能、减小水力损失提供了理论依据。     

漩涡泵内部不稳定流场数值模拟

为了研究漩涡泵内部流场对其外特性的影响,采用RNGk-ε湍流模型和结构化网格技术对漩涡泵内部非定常流动进行数值模拟计算。结果表明,漩涡泵流道内压力变化呈直线分布;流道内纵向漩涡随流量的增大而减小,径向漩涡周期性地脱离叶片被液流带走且随着时间增加而增大;设计工况下,各监测点处压力脉动变化呈周期性分布,从流道进口到出口压力脉动幅值逐步增大;不同工况下,叶片通过频率是压力脉动的主频,其对应的压力脉动幅值随流量增大而增大。     

THE DISTRIBUTION CHARACTERISTICS OF TURBULENCE ON LEESIDE OF WINDBREAKS

The distributive characteristies of turbulence,turbulent vclocity,turbulent intensityand Rcynolds stress,in horizontal and vertical direction on leeward side of windbreak were dis-cussed in this paper.The results show that all the three kinds of parameters of turbulence have thesimilar distributive patterns in lec,their peaks were around 10H for houizontal and Z/H=1 forvertical.The windbreak is important barrier to affect the structure and distribution of wind speedand turvbulence.Porosities of windbreaks could alter the patterns of turbulence,therefore,affect theabilities and functions of windbreaks.     

垂直轴风力机叶片动态失速数值模拟

利用数值计算方法研究了一种典型的大高径比垂直轴风力机叶片动态失速现象。在验证数值计算方法可靠的基础上,结合速度矢量图和涡量图,研究了8 m/s风速时风力机在不同尖速比下叶片动态失速现象以及风轮尺寸改变时风轮动态失速流场及其对风力机功率系数的影响规律。研究表明,尖速比过低,增大弦径比和叶片数均导致叶片动态失速和气流分离呈现加剧趋势,削弱风力机的气动性能。对用于城市风力发电的大高径比垂直轴风力机,应使其在最佳尖速比下运行,同时控制弦径比在0.2~0.4之间,叶片数为3或4,以获得较好的气动性能。     

Tracking the potato late blight pathogen in the atmosphere using unmanned aerial vehicles and Lagrangian modeling

A means for determining the aerial concentration, C (sporangia m⁻³), of plant pathogenic spores at various distances from a source of inoculum is needed to quantify the potential spread of a plant disease. Values of C for Phytophthora infestans sporangia released from an area source of diseased plants in a potato canopy was quantified in three ways: (1) by using Rotorods to sample the air just above the source, (2) by using unmanned aerial vehicles to sample the air at altitudes up to 90 m above the source and at downwind distances up to 500 m from the source, and (3) by using a Lagrangian stochastic simulation of sporangia flight trajectories to tie these two measurements together. Experiments were conducted using three potato crops over two years. Model predictions of time-average, crosswind-integrated concentrations were highly correlated (r = 0.9) with values of C measured using the unmanned aerial vehicles. The model describes the release and dispersal of sporangia from a potato canopy to a downwind distance of 500 m. Thus, it may have utility as a part of an area-wide decision support system by helping to predict risk of disease spread between neighboring or distant potato fields.     

Applying a Lagrangian dispersion analysis to infer carbon dioxide and latent heat fluxes in a corn canopy

Warland and Thurtell (2000) proposed an analytical dispersion Lagrangian analysis (hereafter WT analysis) to relate the mean scalar concentration field to source profiles inside the canopy. The first objective of this study was to evaluate the performance of the WT analysis with existing turbulence statistics parameterizations in a corn canopy, by comparing its inferred net ecosystem CO₂ exchange (NEE) and latent heat flux (λE) with eddy covariance measurements. The second objective was to assess the performance of the WT analysis to infer the soil CO₂ flux. Four parameterizations of turbulence statistics were used to estimate Lagrangian time scale (T_L) and standard deviation of vertical wind velocity (σ_w) profiles. The estimated T_L and σ_w profiles were then corrected for atmospheric stability conditions. The field experiment was carried out in a corn field from August to October 2007 and 2008. Profiles of water vapour and CO₂ mixing ratios were measured using a multiport sampling system connected to an infrared gas analyzer. Wind velocity within and above the canopy and eddy covariance measurements over the canopy were taken. The soil respiration, estimated using the WT analysis, was compared to estimates obtained by an empirical model. WT analysis fluxes showed good correlation (R² = 0.77-0.88) with NEE and λE obtained by the eddy covariance technique, but overestimated net fluxes, especially when corrections for atmospheric stability were applied. The optimization of T_L and σ_w profiles using in-canopy turbulence measurements improved the agreement between measured and modeled NEE and λE. Inferred soil CO₂ fluxes were underestimated and were poorly correlated (R² = 0.02-0.01) with estimates obtained using an empirical model based on soil temperature. This poor performance in estimating the soil respiration is likely caused by the decoupling between inside and above canopy flows.     

开顶箱内自然气流的湍流统计特性

The turbulence statistics parameters （variables） of natural airflow within a large Open Top Chamber （OTC）, 4 m in high height and 3 m in diameter, were measured with a three-dimensional ultrasonic anemometer/thermometer at Research Station of Changbai Mountain Forest Ecosystems Jilin Province, China in May 2004, for improving the field application of OTP. Results showed that because of the physical limitation, turbulence within OTC exhibited unique map compared with that of natural environments. There were clear daily pat- terns for most parameters. Turbulence here seemed to be isotropic and closely linked at all directions. Shape of eddies looked like a ＇cylinder＇ which was very similar to the shape of OTC. Continuous airflow was always interpreted by large scale eddies from top of OTC and showed high interactive intermittence at all directions.     

基于小波和双谱分析的湍流相干结构辨

为了从湍流信号中获取更多关于相干结构的定量信息,提出了一种基于小波和双谱分析的辨识相干结构的方法.该方法通过双谱和互相关分析合理地得到了包含相干结构信息的大涡信号,利用小波变换有效地提取出表征湍流多尺度相干结构的信号成份.建立了基于小波分析辨识湍流含能尺度的能量最大准则,以沟槽壁面减阻机理实验的湍流数据分析为例,验证了该方法的合理性和可靠性.     

水泵吸水池流场PIV分析

水泵吸水池内部的流场很复杂，特别是在吸入管的周围，分布着十分复杂的涡。随着流量的变化，这些涡的位置和强度也相应地变化，这也是吸水池影响水泵系统性能的直接原因。一旦吸水池内部结构确定，影响其流场的因素就是来流情况。本文使用PIV技术对不同来流情况下吸入管附近的流场进行测量，从而得到该吸水池对不同来流的适应性。     

湍流模型的发展及其在内燃机CFD中的应用

从FLUENT软件出发,着重论述了湍流模型的理论和发展,论述了不同模型的适用范围和缺陷,有助于针对不同内燃机的流动过程选择恰当的模型,同时对计算结果作出合理分析。