考虑诱导速度的螺旋桨敞水性能CFD模拟

螺旋桨工作时在其周围形成诱导速度场,诱导速度随到桨叶距离的增大而衰减。采用CFD方法模拟螺旋桨敞水性能时,只能截取有限尺度的流域进行计算,此时计算域边界上诱导速度并不为零,将进口速度设为进速是近似的。一般采用足够大的计算域,使螺旋桨前方及侧面边界尽量远离桨叶。为了在较小的计算域中实现螺旋桨敞水性能的准确预报,提出在设定进口速度时计入螺旋桨诱导速度的CFD模拟方法。应用升力面方法计算诱导速度,将进口速度设为进速与诱导速度之和。逐步减小计算域尺度,考察敞水性能及压力分布计算结果的变化情况及精度。算例比较表明:通过考虑诱导速度,可以大幅度减小进口与螺旋桨的距离而不降低计算精度。     

基于数据融合降低气温测量辐射误差的仿真分析与试验研究

地表气温上升速度约为0.1℃/(10 a),然而受太阳辐射影响,地面气象站观测到的气温会高于真实大气温度,存在1℃量级的辐射误差.因此,本文提出了一种基于数据融合的铝壳温度传感器设计.首先,利用流体动力学方法计算温度传感器在不同环境条件下的辐射误差.其次,为获得连续辐射误差结果,利用神经网络算法对辐射误差数值计算结果进...     

风电场流场特性及风机布局数值模拟研究

针对风电场流场特性研究对风力机工作性能提高的重要意义,采用计算流体力学(CFD)方法在单机风力机模拟验证的基础上,对某风电场单风力机和三种布局条件下的风电场流场特性进行了数值模拟研究.考察了不同布局条件下风电场速度、叶轮表面压力以及湍流涡的分布特性.结果表明:叶轮后方尾流效应明显,速度损失随着相对距离的增加而逐渐减小,...     

基于Fluent的空气射流切削式反循环钻头参数优化

针对黄土地层,提出利用空气代替钻井液的反循环气体喷射技术。但现有技术对反循环气体喷射钻头切削土体的能力没有具体优化讨论。利用fluent软件,优化反循环喷射钻头结构参数,对不同底喷孔直径、底喷孔数量、底喷孔扩大段直径、底喷孔扩大段数量、喷射孔数量5个结构参数进行模拟分析。分析结果表明,在进风流量一定的情况下,增加底喷孔的数量或增大底喷孔的直径会削弱钻头的空气射流切削能力和反循环能力。底喷孔直径为3 mm,底喷孔个数为2个,底喷孔扩大段直径为8 mm,底喷孔扩大段长度为5 mm,内喷孔数量为5个时,反循环喷射钻头喷射能力和反循环能力最优。     

基于SRTM资料的小海岛CFD计算模型构建——以东澳岛为例

提出了一种利用SRTM资料构建海岛CFD计算模型的技术方法,并以珠江口的东澳岛为对象,进行了模型构建试验及边界层风场的数值模拟试验.实验结果表明,SRTM资料作为开源的资料,可有效地解析空间尺度在1 km以内数量级的海岛地形,并可以此为基础构建用于CFD模拟的计算模型,真实地刻画出岛屿的地形.利用计算模型进行的模拟试验表明,岛屿地形对风场的影响明显,且这种影响可以被计算模型有效地描述.所提出的技术未来在海岛风资源评估、风电场选址、污染扩散等领域有望发挥作用.     

Sail pressures from full-scale, wind-tunnel and numerical investigations

The main results of a two-year project aimed at comparing full-scale tests, wind tunnel tests, and numerical analysis predictions are presented. Pressure measurements were obtained from both full-scale tests and wind tunnel tests, in upwind and downwind conditions. The upwind wind tunnel test condition was modelled using a Vortex Lattice code, while the downwind wind tunnel test was modelled using a Navier-Stokes code. The pressures obtained from the three different methods are compared on three horizontal sections of the headsail, mainsail and asymmetric spinnaker. In general the pressure from the three experiments showed good agreement. In particular, very good agreement was obtained between the numerical computations and the wind tunnel test results. Conversely, the results from the downwind full-scale pressure measurements showed less similarity due to a slightly tightened trim being used for the spinnaker in the on-water tests. Full-scale tests allow the action of unsteadiness due to the wind, wave and yacht movements to affect the results. This unstable environment caused the asymmetric spinnaker to move around, and a tightened trim was required to prevent the spinnaker from collapsing.     

CFD方法在街巷气象场模拟和预测中的应用

为开发建立米级分辨率的城市街巷气象场模拟预测方案,以PHOENICS为例介绍了计算流体力学（CFD）方法的原理,讨论了该方法应用于街巷气象要素数值计算的可行性。提出了一种基于CFD模型与高分辨率数值天气预报模式嵌套的街渠气象场模拟预测方案,并对边界嵌套问题作了多种敏感性分析,表明嵌套对街渠气象场计算具有必要性和可行性;另外,还讨论了分辨率对计算结果和计算耗时的影响;最后,用实例介绍了本方案的应用,并讨论了本方法的应用前景。     

Flow structures at an idealized bifurcation: a numerical experiment

River bifurcations are key nodes within braided river systems controlling the flow and sediment partitioning and therefore the dynamics of the river braiding process. Recent research has shown that certain geometrical configurations induce instabilities that lead to downstream mid‐channel bar formation and the formation of bifurcations. However, we currently have a poor understanding of the flow division process within bifurcations and the flow dynamics in the downstream bifurcates, both of which are needed to understand bifurcation stability. This paper presents results of a numerical sensitivity experiment undertaken using computational fluid dynamics (CFD) with the purpose of understanding the flow dynamics of a series of idealized bifurcations. A geometric sensitivity analysis is undertaken for a range of channel slopes (0.005 to 0.03), bifurcation angles (22° to 42°) and a restricted set of inflow conditions based upon simulating flow through meander bends with different curvature on the flow field dynamics through the bifurcation. The results demonstrate that the overall slope of the bifurcation affects the velocity of flow through the bifurcation and when slope asymmetry is introduced, the flow structures in the bifurcation are modified. In terms of bifurcation evolution the most important observation appears to be that once slope asymmetry is greater than 0.2 the flow within the steep bifurcate shows potential instability and the potential for alternate channel bar formation. Bifurcation angle also defines the flow structures within the bifurcation with an increase in bifurcation angle increasing the flow velocity down both bifurcates. However, redistributive effects of secondary circulation caused by upstream curvature can very easily counter the effects of local bifurcation characteristics. Copyright © 2011 John Wiley & Sons, Ltd.     

Numerical modelling of a point-absorbing wave energy converter in irregular and extreme waves

Based on the Navier-Stokes (RANS) equations, a three-dimensional (3-D) mathematical model for the hydrodynamics and structural dynamics of a floating point-absorbing wave energy converter (WEC) with a stroke control system in irregular and extreme waves is presented. The model is validated by a comparison of the numerical results with the wave tank experiment results of other researchers. The validated model is then utilized to examine the effect of wave height on structure displacements and connection rope tension. In the examined cases, the differences in WEC’s performance exhibited by an inviscid fluid and a viscous fluid can be neglected. Our results also reveal that the differences in behavior predicted by boundary element method (BEM) and the RANS-based method can be significant and vary considerably, depending on wave height.     

Investigations on 3D effects and correlation between wave height and lip submergence of an offshore stationary OWC wave energy converter

Understanding the hydrodynamic interactions between ocean waves and the oscillating water column (OWC) wave energy converter is crucial for improving the device performance. Most previous relevant studies have focused on testing onshore and offshore OWCs using 2D models and wave flumes. Conversely, this paper provides experimental results for a 3D offshore stationary OWC device subjected to regular waves of different heights and periods under a constant power take–off (PTO) damping simulated by an orifice plate of fixed diameter. In addition, a 3D computational fluid dynamics (CFD) model based on the RANS equations and volume of fluid (VOF) surface capturing scheme was developed and validated against the experimental data. Following the validation stage, an extensive campaign of computational tests was performed to (1) discover the impact of testing such an offshore OWC in a 2D domain or a wave flume on device efficiency and (2) investigate the correlation between the incoming wave height and the OWC front wall draught for a maximum efficiency via testing several front lip draughts for two different rear lip draughts under two wave heights and a constant PTO damping. It is found that the 2D and wave flume modelling of an offshore OWC significantly overestimate the overall power extraction efficiency, especially for wave frequencies higher than the chamber resonant frequency. Furthermore, a front lip submergence equal to the wave amplitude affords maximum efficiency whilst preventing air leakage, hence it is recommended that the front lip draught is minimized.