复合材料自动铺带技术研究(I)——“自然路径”特性分析及算法

分析了可展面上“自然路径”的几何本质,推演证明其在可展曲面上与测地线的等价性。应用和拓展可展面“自然路径”数值算法,在一般曲面上引入边界控制点调整预浸带中心点以减小预浸带变形、实现铺放,构造了一般曲面“自然路径”求解格式。     

竖直平板间湍流自然对流中螺旋羽流结构的实验研究

应用粒子图像测速技术（PIV）对竖直平板间水的温差湍流自然对流的流场进行了测量,并由测量所获得的速度场获取了涡量分布和散度分布。测量结果表明,在流场中的竖直展向截面和水平流向截面上都存在大尺度涡流结构,而且在部分涡量集中区域同时具有正的或者负的散度集中,速度矢量分布也表明水平截面上的这部分涡流结构呈现着清晰的源或汇的特征。这些现象都表明这部分旋转着的流体不但有切向速度,还有径向速度。这意味着这部分流体在旋转的同时也有向上或向下的运动,即同时具有在同方向上的涡量和速度,即螺度,而这是螺旋羽流结构的特征。这些涡结构,尤其是水平流向截面上具有径向速度的涡流结构的存在证实了竖直平板之间的湍流自然对流流场中大尺度的螺旋羽流结构的存在。     

强制对流对 Al-4.5wt%Cu 合金枝晶生长的影响

研究了ACRT（坩埚加速旋转技术）对Al-4.5wt%Cu合金在静态温度梯度GL为120℃/cm时枝晶生长的影响。实验发现,在给定抽拉速度下,枝晶一次间距λ1随着坩埚旋转强度的增大而减小;而在给定的坩埚旋转参数下,λ1随着抽拉速度的增大而降低。经过线性回归,发现λ1∝V-b,此处V为生长速度;b的取值范围为0.31～0.38,并随着坩埚旋转强度的增大而减小。此外,坩埚加速旋转产生的强制对流限制了枝晶高次分枝的生长,促使一次枝晶生长过程中的分叉。通过对强制对流的具体分析,解释了ACRT对枝晶生长影响的机理。     

高位进气、径向出流的旋转腔内流动与换热的数值研究

用标准k-ε模型模拟了航空发动机涡轮盘冷却系统的高位进气、径向出流盘腔模型的湍流流场和温度场,分析了其盘面平均Nu数随旋转雷诺数Reω和进气雷诺数Re的变化。     

不同密度比下旋转方通道内流场和换热的数值模拟

在雷诺数为25000、旋转数为0.24、密度比为0.07~0.22的范围内,以数值计算的方法模拟了旋转方通道内三维流场及换热分布,与公开文献中的换热实验结果进行的对比表明,低雷诺数k-ω模型的计算结果与实验值吻合得相对较好;重点研究了旋转状态下冷气密度比对通道内流场和换热的影响,分析了哥氏力和浮升力在通道中的交互作用机理,结果表明,哥氏力引发的截面二次流是造成旋转通道前后缘换热差异的主要因素,浮升力加剧了通道内主流型的偏移,同时,其在前缘表面诱发的流体分离改变了局部湍流强度和换热分布。     

A 2-D comparison of ionospheric convection derived from SuperDARN and DMSP measurements

Ion drift vectors measured by the DMSP satellites are compared with plasma convection vectors obtained by the SuperDARN HF radars through the standard Map Potential algorithm of Ruohoniemi and Baker [Ruohoniemi, M., Baker, K.B. Large-scale imaging of high-latitude convection with super dual auroral radar network HF radar observations. J. Geophys. Res. 103, 20797–20811, 1998]. Despite significant data spread, the agreement can be qualified as reasonable for a data set comprising of 149 satellite passes over the Northern Hemisphere at high latitudes. The slope of the best-fit line relating SuperDARN and DMSP velocity magnitudes is of the order of 0.3 with a tendency for the SuperDARN velocities to be smaller. The agreement between the azimuths of the ion drift and convection is better with the slope of the best-fit line being close to 1. It is shown that consistency between the radar and satellite measurements is much better if the SuperDARN line-of-sight velocities are compared with the DMSP cross-track ion drifts for events showing slow spatial and temporal variations of the convection. If areas of strong convection changes are included into comparison, the degree of agreement deteriorates drastically. This result implies that differences in the spatial and temporal resolutions of DMSP and SuperDARN measurements are crucial factors contributing to the observed discrepancies. In addition, some differences are introduced when the SuperDARN line-of-sight velocities are filtered and reprocessed into vectors with the application of a background convection model.     

EXTENDED SELF SIMILARITY OF PASSIVE SCALAR IN RAYLEIGH-BENARD CONVECTION FLOW BASED ON WAVELET TRANSFORM

Wavelet transform is used to analyze the scaling rule convection flow from two aspects. By utilizing the method of extended self similarity (ESS), one can find the obtained scaling exponent agrees well with the one obtained from the temperature data in a experiment of wind tunnel. And then we propose a newly defined formula based on wavelet transform, and can determine the scaling exponent ξ(q) of temperature data. The obtained results demonstrate that we can correctly extract ξ(q) by using the method which is named as wavelet transform maximum modulus (WTMM).``     

磁尾等离子体片对流对亚暴的影响

采用2(1/2)维全粒子电磁模拟方法研究了等离子体片中稳态对流及局地爆发高速流对磁层亚暴触发过程的影响.研究发现,地向瞬时局地高速流可触发磁场重联,导致储存于磁尾磁场能量的快速释放.但是,等离子体片稳态对流可抑制磁尾磁场重联过程.此项研究结果表明,局地爆发高速流能够触发磁层亚暴;而行星际磁场(IMF)持续南向时的稳态磁层对流期间,不易发生亚暴.      

Thick exchange layer evaporation model with natural convection effect and evaporation experimental study for multicomponent droplet

In order to investigate the high-temperature evaporation characteristics of multicomponent liquid fuel, three kinds of blended fuel: n-heptane/n-decane/RP-3 aviation kerosene-ethanol were experimentally studied with and without forced convection. Further, based on zero-diffusion and infinite diffusion concept, this study expanded Thick Exchange Layer evaporation model with Natural Convection effect (NC-TEL) to multicomponent liquid fuels. The experimental results show that the droplet evaporation rate increases significantly with the increase of ambient temperature. Higher temperature leads to more significant relationships between the composition ratio and the evaporation rate. The effect of forced convection is not obviously under the circumstance in this paper. Then, the evaporation models were validated by experimental data. In general, the new NC-TEL model behaves better than the Ranz-Marshall (R-M) model, and the prediction accuracy at high temperature is improved by 8% to 35%. In lower temperature conditions, the prediction of zero-diffusion NC-TEL model is better than the infinite diffusion NC-TEL model. In high-temperature conditions, for n-heptane-ethanol droplet, the predictions of NC-TEL model are accurate, but for n-decane/RP-3 aviation kerosene-ethanol, the predictions are lower than experimental results. This may be caused by the micro-explosion phenomenon and the Marangoni phenomenon.