导叶叶片数对离心泵特性的影响

在比转速n_s=71的离心泵研发过程中,针对叶片数z=5的叶轮,为选择适宜叶片数的导叶,采用CFX软件对单级研发泵进行非定常数值模拟研究,分析了不同工况下导叶叶片数分别为6、7、8时泵的外特性、压力脉动和叶轮径向力,针对小流量工况径向力的较大差异,进一步对比了叶轮内流场。结果表明,减少导叶叶片数可提高较大流量工况的扬程和效率,但可能导致小流量扬程下降;小流量区间导叶叶片数对压力脉动的影响较为复杂,而较大流量工况增加导叶叶片数有益于改善压力脉动;此外,导叶叶片数越多,非额定工况的叶轮径向力越小,特别是在小流量工况,增加导叶叶片数提高了叶轮流场的均匀性,径向力缩小约4倍。最终对整体性能较优的7叶片导叶进行排产和试验,其中扬程计算误差不超过5.9%,表明数值模拟结果具有一定精度。     

带可调进口导叶离心压缩机的性能分析

以数值模拟的方式对某带可调进口导叶的离心压缩机级内部流动进行了分析研究。对计算得到的性能曲线及相对速度矢量图的分析表明，进口导叶正旋绕时性能曲线向小流量区移动，负旋绕时向大流量区移动；经最高效率点进入小流量区后效率下降较快；在进口导叶大安装角情况下，在大的流量范围内导叶区域均存在显著分离，大流量时短叶片吸力面前部有回流区，小流量时长叶片吸力面上发生分离。     

基于CFD的轴流泵后置导叶水力性能分析

为了解轴流泵后置导叶的水力性能,基于RNG湍流模型,采用计算流体动力学CFD软件Fluent,应用SIMPLIEC算法对轴流泵模型装置全流道进行了数值模拟,分析了四种不同流量下导叶体的内部流动特性,研究了导叶的水力性能。结果表明,导叶的水力损失随流量的增加先减小后增大;在设计流量处导叶水力损失最小,导叶压力转换能力最好;小流量下叶轮进出口处水流流态紊乱,导叶流道内出现漩涡回流,是导致导叶水力损失较大的主要原因;大流量下叶轮出口水流轴向速度较大,水流导叶进口边撞击将导致导叶体水力损失增加,水力性能下降。     

带有可调导叶的径流涡轮气动特性的研究

采用数值模拟的方法对单级径向涡轮在导向叶栅的不同开度、不同工况下的全流场进行了三维模拟分析。研究表明,可调导叶对涡轮性能的影响是叶栅收敛度、气流冲角与出气角的综合影响。在综合考虑了导叶损失以及叶轮损失的基础上,提出了变几何径向涡轮随速比变化的调节方案。     

基于水轮机导叶转角推求导叶开度圆直径的方法

鉴于反击式水轮机活动导叶开度大多采用导叶转角描述,而在水电工程初步设计阶段开展的相关设计计算工作中,仍采用导叶开度圆直径描述现状,以活动导叶数为24只的圆柱式导水机构为基础,提出了水轮机导叶转角与导叶开度圆直径之间的转换公式。同时,通过对一系列典型导叶布置图的分析,结合数值分析方法,对公式中的修正系数给出了明确的解析表达式,并验证了表达式的可靠性。     

多泥沙高水头水电站混流式水轮机导叶泥沙磨损数值研究与试验

为研究新疆夏特高水头水电站水轮机导叶的泥沙磨损情况,采用标准k-ε湍流模型和Particle模型,在小流量工况下开展了HLA351-LJ-275水轮机导叶流体域的固液两相流数值模拟,分析其内部流动特性,并结合该模型水轮机单流道泥沙磨损试验得到导叶磨损的主要部位和磨损程度。结果表明:固定导叶磨损量较小,活动导叶磨损部位主要集中在头部和尾部,磨损量较大。结合数值计算与试验结果,通过其泥沙磨损特征规律,拟合并建立了固定导叶及活动导叶的磨损量公式,对多泥沙高水头水电站导水机构磨损寿命的预估和导水机构运行维护具有重要意义。     

基于CFX单圆弧空间导叶斜流泵的数值模拟

利用流体计算软件ANSYS-CFX,采用基于三维不可压缩流体的N-S方程和标准κ-ε湍流模型对带有单圆弧空间导叶的斜流泵进行了数值模拟,通过分析其整体静压分布、速度分布及三个典型工况下叶轮叶片的静压分布、吸力面的速度分布、导叶片压力及速度分布等,揭示了其内部流场的主要特征,预测了泵的水力性能。对比了模拟结果与试验结果,验证了数值模拟的可靠性,说明带单圆弧空间导叶的斜流泵在一定流量范围内能满足工程实际的需要,且在加工制造方面优于扭曲的空间导叶。     

径向导叶对高速离心泵非定常流动影响的分析

应用计算流体力学技术对带导叶与不带导叶高速离心泵的内部流场进行定常及非定常数值模拟,从而预测出带导叶与不带导叶两种方案下的外特性曲线走势情况。同时得到了流体流经关键位置时在不同工况下的压力脉动情况,并对相应的时域图及频域图进行了对比分析。结果表明,带有导叶的高速离心泵相比于无导叶离心泵扬程较高,扬程曲线更加平缓,同时在大流量工况下,高速离心泵效率更高也更稳定。从时域图分析,不同工况下两种方案中的高速离心泵压力脉动存在明显的周期性,其中带有导叶的高速离心泵在大流量工况下压力脉动幅值相对较小,不带导叶的高速离心泵在小流量下压力脉动幅值相对较小;从频域图分析看,两种方案中的高速泵都是在一倍叶频处存在较大峰值,即动静干涉作用是引起压力脉动的主要因素,同时通过对比,在不同工况下带有导叶的高速离心泵在二倍叶频处峰值较小,说明添加径向导叶对缓解动静干涉起到一定作用。通过比较不同方案下监测点压力脉动平均值及峰值曲线图,说明在高速泵中加装径向导叶可以有效地发挥扩压作用,降低液流速度,充分将速度能转化为压能。结合上述结论,可以得出带导叶高速离心泵适合在大流量高工况下运行,如消防灭火,石油化工,航空航天等领域。     

导叶安放角对核主泵水力性能的影响

为研究导叶安放角对核主泵水力性能的影响,对5种不同导叶安放角下的核主泵模型进行定常数值计算,并基于熵产理论分析了泵内流动损失变化。结果表明：在设计流量和大流量工况下,DY4模型的扬程和效率最高,最佳效率出现在设计流量下,相比DY1模型提升了3.68%;在设计流量和大流量工况下,DY4模型的压力和速度流线分布均匀且变化平稳,导叶和蜗壳内流动损失占比最低,高流动损失区域面积较小;在小流量工况下,DY5模型的扬程和效率最高,最高效率出现在流量比为0.8时;DY5模型导叶和蜗壳内静压明显高于其他模型,流道内速度变化均匀,导叶和蜗壳内流动损失最低。     

导叶数目对两级动叶可调轴流风机性能的影响

为研究导叶数目对轴流风机性能的影响,文章以某两级动叶可调轴流风机为研究对象,模拟了第一、二级和两级导叶数目变化时的风机性能,并分析了其对风机性能和流场特征的影响。研究结果表明:导叶数目减少后,风机性能整体高于原风机;导叶数目增加后,风机性能未必高于原风机。其中,两级导叶数目均减至21片时的风机性能最佳,在设计工况下,全压提升119 Pa,效率提升0.4%。在此方案下,第二级动叶做功能力和导叶扩压能力均得到提升,导叶数目变化对下游流场有显著影响,而对上游流场影响较小。     

离心压缩机进口导叶叶型的进一步研究

为提高离心压缩机进口导叶的质量流量调节能力,以原研究成果为基础对导叶叶型做进一步研究。通过数值模拟计算,对不同厚度弯叶型和不同弯度位置导叶的质量流量调节能力进行对比分析。结果表明,虽然减小弯叶型的厚度可扩大其质量流量调节范围,却增加了流动损失,使压缩机效率下降;将弯叶型最大挠度位置向后移,可有效提高导叶的质量流量调节能力,且其产生的损失对压缩机性能影响不大。最终选择出适合于导叶进行质量流量调节的最佳叶型,减少了压缩气体的排空浪费。     

Impulse turbine with 3D guide vanes for wave energy conversion

In this study, in order to achieve further improvement of the performance of an impulse turbine with fixed guide vanes for wave energy conversion, the effect of guide vane shape on the performance was investigated by experiment. The investigation was performed by model testing under steady flow condition. As a result, it was found that the efficiency of the turbine with 3D guide vanes are slightly superior to that of the turbine with 2D guide vanes because of the increase of torque by means of 3D guide vane, though pressure drop across the turbine for the 3D case is slightly higher than that for the 2D case.     

前置导叶对双吸离心泵性能影响试验研究

为了优化离心泵运行工况,运用叶轮机械设计、前置导叶预旋调节的基本理论,并结合诱导轮设计理论,设计了两种不同叶高的双吸泵前置诱导叶片.对带有不同叶高前置叶片的双吸泵进行了试验研究.研究结果表明:带有诱导叶片的双吸泵虽然扬程略有降低,且在大流量区域效率降低,但其功率消耗降低,最大可节能3.34%,且高效区往小流量偏移;14 mm叶高诱导叶片调节效果明显优于20 mm叶高诱导叶片,且能够有效地将双吸泵高效区往小流量偏移,同时降低离心泵功率消耗.     

Computed effect of guide vane shape on performance of impulse turbine for wave energy conversion

This paper deals with the computational fluid dynamics (CFD) analysis on effect of guide vane shape on performance of impulse turbine for wave energy conversion. Initially, experiments have been conducted on the impulse turbine to validate the present CFD method and to analyse the aerodynamics in rotor and guide vanes, which demonstrates the necessity to improve the guide vanes shape. The results showed that the downstream guide vanes make considerable total pressure drop leads low performance of the turbine and hence three‐dimensional (3‐D) inlet and downstream guide vanes have been designed based on well‐known vortex theory to improve the efficiency of the turbine. In order to prove the improvement in efficiency due to 3‐D guide vanes, CFD analysis has been made on impulse turbine with 2‐D and 3‐D guide vanes for various flow coefficients. As a result, it is seen that the present CFD model can predict the experimental values with reasonable accuracy. Also, it is showed from the numerical results that the efficiency of the turbine can be improved by average of 4.5 percentage points by incorporating 3‐D guide vanes instead of 2‐D guide vanes. The physical reason for improvement in efficiency of the turbine due to 3‐D guide vanes has been explained with the CFD flow insight pictures. As the turbine operates in fluctuating flow conditions, the performance of the turbine with 2‐D and 3‐D guide vanes have been calculated numerically using quasi‐steady analysis. Furthermore, the performance of the turbine has been predicted for one year based on Irish wave climate to show the feasibility of using 3‐D guide vanes in actual sea wave conditions. Copyright © 2005 John Wiley & Sons, Ltd.     

Design and experimental validation of the inlet guide vane system of a mini hydraulic bulb-turbine

The paper presents a fast design method for the inlet guide vanes of low-cost mini hydraulic bulb turbines. The guide vanes are positioned between two conical surfaces with a common vertex and have constant thickness distribution, except close to the leading and the trailing edges. The conical-walled inlet guide vane row is designed using a quasi-three-dimensional calculation method, by prescribing the angular-momentum distribution along the span at the outlet section of the guide vanes.The meridional through-flow is computed by a streamline curvature method and the blade-to-blade flow by a singularity surface method. The stagger angle and the vane camber are computed to fulfil the required design circulation and zero-incidence flow at the leading edge. The final vane shape is a single-curvature surface with straight leading and trailing edges. To validate the design method, a conical-walled inlet guide vane row nozzle-model with six fixed vanes was designed, manufactured and tested in an airflow rig. Traversing measurements along the circumferential and radial directions were made with a five-hole probe.The experimental results are compared with the prescribed design conditions and with numerical results from the three-dimensional inviscid and viscous flow computed with the FLUENT code.     

变几何涡轮可调导叶瞬时转动气动特性研究

为探究单级变几何涡轮(VGT)在导叶转动过程中的过渡态性能,对某动力涡轮进行了非定常数值计算,应用动网格技术实现导叶转角的改变,并对导叶通道开大或关小过渡过程中涡轮性能进行了分析。结果表明：导叶转角从0°变化到-5°时,单级涡轮效率逐渐下降1.6%,从0°变化到6°时,效率逐渐提高0.5%;质量流量和导叶出口绝对气流角随转角改变接近线性变化,而动叶出口相对气流角、熵增、效率和导叶出口总压损失等随转角改变呈抛物线型变化;过渡态下导叶流场内损失变化主要受上、下端壁处间隙泄漏涡影响,动叶出口熵增变化规律主要受动叶吸力侧泄漏涡和下部通道涡影响,其中下部通道涡的改变是引起熵增变化的主要原因。     

Performance analysis of a centrifugal compressor with variable inlet guide vanes

The flow in a centrifugal compressor stage with variable inlet guide vanes (VIGVs) is investigated by numerical simulation in this paper. Analysis of the performance curves and relative velocity vectograms indicates that performance curves shift toward small flow domain when VIGVs turn positively, and toward large flow domain when VIGVs turn negatively. Stage efficiency drops quickly after work condition enters a small flow domain through the peak efficiency point. Under the circumstance of large setting angles of the guide vanes, there exist obvious flow separations in guide vane passages within wide flow ranges, and back flow regions can be located at the front of splitter suction surfaces under large flow conditions, while under the condition of small flow, flow separations occur on suction surfaces of long blades. __________ Translated from Journal of Power Engineering, 2006, 26(6): 804–807 [译自: 动力工程]     

Design method of guide vane for Wells turbine

Guide vanes are installed in the Wells turbine in order to improve its efficiency, self-rotating characteristics and off design performance with stall. This work attempts to explain the role of these guide vanes on the basis of momentum theory. It is shown that the upstream vanes are more effective in enhancing efficiency than the downstream ones. A design method for guide vanes is suggested based on experimental data and potential theory. Experimental studies carried out by the author confirm the theory proposed.     

基于CFD的导叶进口角对轴流泵水力性能的影响

为研究后置导叶进口安放角对轴流泵水力性能的影响,在常规导叶基础上将导叶分为进口段和出口段两部分,运用数值模拟的方法研究了5种导叶进口安放角对轴流泵泵段水力性能的影响。结果表明,轴流泵在偏离设计工况下运行时,通过调节导叶进口角度可以减小导叶进口冲角,改善导叶体内流态。在后置导叶原设计进口角度的基础上,沿旋转轴顺时针调节适当角度可提高大流量处的泵段效率,逆时针调节适当角度可提高小流量处的泵段效率。不同导叶进口角主要是保证多种工况下水流无撞击进入导叶室,对泵段的其他过流部件水力性能基本无影响。研究成果有助于轴流泵导叶性能的优化设计。