关联维数在尾水管压力脉动分析中的应用

以黄壁庄机组尾水管压力脉动试验的实测信号为例,对时域信号进行了频谱分析,并对在不同的工况下尾水管压力脉动信号进行嵌入维数和关联维数分析。结果表明,当嵌入维数大于等于18时,关联维数趋于稳定值。不同工况下水轮机尾水管压力脉动的关联维数也不同,当导叶开度为50.70%时,分形关联维数为3.456 6;导叶开度为62.85%时,分形关联维数为3.388 1。因此,关联维数可以作为对水轮机尾水管压力脉动情况进行识别的指标,可以指导电站的稳定运行。     

4种湍流模型对混流式水轮机压力脉动模拟的比较

采用RNGk-ε模型、Realizable k-ε模型、Transition SST模型和DES模型,在4种网格尺度下对模型混流式水轮机三维全流道非定常湍流进行模拟.在试验验证的基础上,分析各模型对水轮机压力脉动模拟的适应性,并进行网格无关性分析.分析结果表明:4种湍流模型都可以模拟出尾水管偏心涡带的形态,但尾水涡带在相位上不同,压力脉动的主频或振幅有差别;湍流模型与网格尺度不是单调线性关系,甚至相反;Transition SST模型比RNGk-ε模型、Realizable k-ε模型、DES模型对水轮机压力脉动模拟的适应性更好,在不同网格尺度下预测的压力脉动主频、振幅和试验结果更加吻合.     

喷动流化床内木屑流动特性的研究(Ⅰ)

为了开发喷动流化床生物质裂解反应器,建立了一内径为150mm的有机玻璃冷模实验装置,考察了喷动气和流化气流速、木屑粒子的加入量及导向管位置对床层流动特性的影响。发现喷动气的旁路现象对粒子循环速率、中心喷泉高度及床层压降都有显著影响。流化气的加入,可抑制喷动气的旁路趋势。实验还发现,木屑粒子与煤粒这类刚性粒子的流动特性不完全相同,木屑粒子之间相互作用较大。     

水电站尾水管CAD的参数化实体造型方法及实现

提出了参数化实体造型的方法．该方法可以根据水轮机的类型自动选择尾水管的型号，根据转轮直径大小自动检索及计算尾水管的几何尺寸．由这些参数通过实体造型可自动生成尾水管的三维实体图，进而生成其单线图及任意截面的型线图     

高压涡轮叶顶间隙变化的数值分析

利用有限元分析软件分析了某型高压涡轮叶顶间隙在不同工况下随时间的变化。采用分段加载方法对模型施加温度和压力边界条件。计算结果与实验数据的对比分析表明:涡轮叶片位移对叶顶间隙变化的贡献不大,温度和转速是影响轮盘径向尺寸变化的主要因素,而温度是影响机匣和叶片变形的主要因素。     

余热排出泵小破口失水事故空化特性数值分析

为研究小破口失水事故工况下余热排出泵内部空化流动特性,基于Rayleigh-Plesset方程的混合物均相流空化模型和剪切应力运输SST湍流模型,对余热排出泵高温高压环境下叶轮内空化流动进行全流道数值计算。根据计算结果获得了余热排出泵小破口严重事故工况下扬程和效率的衰减曲线及空化发生的初始压力,捕捉到泵内空化的发生、发展过程。研究结果表明:当环境压力降低至大约1.15 MPa时,叶片吸力面进水边靠近前盖板处开始出现空泡,随着环境压力的降低,空泡分布区域及空泡体积分数不断扩大;当压力降低至1.143 MPa时,叶轮内部最大空泡体积分数达到50.17%,严重空化时,叶片工作面会有空泡聚集并造成叶轮流道严重堵塞致使泵扬程急剧下降。通过分析空化发生的状况得出空化发生的初始压力,为余热排出泵的设计提供一定的参考。     

Pressure fluctuation propagation of a pump turbine at pump mode under low head condition

Pressure fluctuation at the vaneless space and vanes passages is one of the most important problems for the stable operation of a pump turbine.The fluctuation appears in any operating condition.Much research has been done on the pressure fluctuation of hydraulic machinery.However,the details of pressure fluctuation propagation of the pump turbine at the pump mode have not been revealed.The modern pump turbine with high water head requires the runner to be"flat",which would induce pressure fluctuation more easily than the low head pump turbine.In this article,a high head pump turbine model is used as the research object.As the pressure fluctuation at off-design point is more serious than at the design point,the low head condition is chosen as the research condition.Pressure fluctuation at the vaneless space and vanes passages is predicted by the computational fluid dynamics method based on k-?shear stress transport model.The experiment conducted on the test rig of the Harbin Institute of Large Electrical Machinery is used to verify the simulation method.It proves that the numerical method is a feasible way to research the fluctuation under this operating condition.The pressure fluctuation along the passage direction is analyzed at time and frequency domains.It is affected mainly by the interaction between the runner and vanes.In the circumferential direction,the influence of the special stay vane on the pressure fluctuation is got.The amplitude in the high-pressure side passage of that vane is lower than that in the other side.The study provides a basic understanding of the pressure fluctuation of a pump turbine and could be used as a reference to improve the operation stability of it.     

Experimental investigation on unsteady pressure fluctuation of rotor tip region in high pressure stage of a vaneless counter-rotating turbine

An experimental investigation has been performed to study the unsteady pressure fluctuation of rotor tip region in high pressure stage of a vaneless counter-rotating turbine. The experiment is carried out on a blow-down short duration turbine facility. The investigation indicates that the blow-down short duration turbine facility is capable of substituting continuous turbine facilities in most turbine testing. Through this experimental investigation, a distinct blade-to-blade variation is observed. The results indicate that the combined effects of vane wake, tip leakage flow, complicated wave systems and rotor wake induce the remarkable blade-to-blade variations. The results also show that the unsteady effect is intensified along the flow direction. Supported by the Award Fund of the President of CAS     

波纹管内层流脉动传热和阻力特性的数值研究

为探讨波纹管和脉动流同时使用能否实现复合强化传热的效果,利用计算流体力学软件Fluent数值模拟了波纹管在管内流体发生周期性速度变化条件下的传热和阻力特性．模拟的边界条件为：管壁温度293K;管内工质为水,入口温度333K,平均流速0．02m／s,脉动频率厂分别取2、4、5、8、10Hz,振幅A分别取0．2、0．4、0．6、0．8、1;出口压力为0．通过分析传热强化系数、沿程阻力增强系数、效应评价准则数,结果显示：管内脉动流既能强化波纹管的传热也会弱化传热;相比稳态流条件,传热最大能被强化约5．9％;脉动流会增大波纹管的沿程阻力;综合考虑传热的强化作用和流动阻力的增加,在A≥O．8且,≥4Hz条件下,管内脉动与波纹管能起到复合强化传热效果;脉动流条件下波节附近漩涡周期性的产生和消失是传热被强化和沿程阻力增加的主要原因．     

Mechanism and numerical analysis of heat transfer enhancement in the core flow along a tube

The present study introduces the principles of enhanced heat transfer in the core flow to form an equivalent thermal boundary layer in the fully developed laminar tube flow, which consequently enlarges the temperature gradient of the fluid near the tube wall, and thereby enhances the heat transfer between the fluid and the tube wall. At the same time, the increase of flow resistance in the tube is not so obvious. Mechanism analysis and numerical calculation based on air and water have been carried out to verify the principle and method presented in this paper, which may bring positive effects to the design of heat exchanger with high heat transfer efficiency and low flow resistance. Supported by the National Key Basic Research Development Program of China (Grant No. 2007CB206903)     

黄土深基坑桩锚联合支护结构变形与稳定性分析

为保证某临近地铁车站深基坑在施工过程中安全,采用数值模拟的方法分析了该基坑临近地铁车站一侧桩锚联合支护结构在施工过程中的变形情况,并对其进行稳定性分析.分析表明:临近地铁车站一侧基坑支护结构最大侧移发生在离坑顶约7 m处,最大侧移为13.4 mm;最大地表沉降出现在距离基坑边约4m处,最大沉降量为8.81 mm;桩锚联合支护结构具有较好的稳定性,能够有效控制基坑在开挖过程中变形,工程深基坑的开挖没有影响到地铁车站安全.