CFD Simulation of Fixed and Variable Pitch Vertical Axis Tidal Turbine

In this paper, hydrodynamic analysis of vertical axis tidal turbine （both fixed pitch ＆ variable pitch） is numerically analyzed. Two-dimensional numerical modeling ＆ simulation of the unsteady flow through the blades of the turbine is performed using ANSYS CFX, hereafter CFX, which is based on a Reynolds-Averaged Navier-Stokes （RANS） model. A transient simulation is done for fixed pitch and variable pitch vertical axis tidal turbine using a Shear Stress Transport turbulence （SST） scheme. Main hydrodynamic parameters like torque T, combined moment CM, coefficients of performance Cp and coefficient of torque Cr, etc. are investigated. The modeling and meshing of turbine rotor is performed in ICEM-CFD. Moreover, the difference in meshing schemes between fixed pitch and variable pitch is also mentioned. Mesh motion option is employed for variable pitch turbine. This article is one part of the ongoing research on tm＇bine design and developments. The numerical simulation results are validated with well reputed analytical results performed by Edinburgh Design Ltd. The article concludes with a parametric study of turbine performance, comparison between fixed and variable pitch operation for a four-bladed turbine. It is found that for variable pitch we get maximum Ce and peak power at smaller revolution per minute N and tip sped ratio 2.

Experimental Study of Effects of Tip Geometry on the Flow Field in a Turbine Cascade Passage

This study investigates the effects of blade tip geometry on the flow field of a turbine cascade at the incidence angle of 0 degree experimentally. The tests were performed in a low-speed turbine cascade wind tunnel. The Reynolds number based on the blade chord was about 172300 at the exit. Traverses of the exit flow field were made in order to measure the overall performance. The effects of using fiat tip and grooved tip with a chord-wise channel were studied. The case with the flat tip is referenced as the baseline. The tip clearances are all 1 mm measuring 0.84 percent of the blade span. The depth of channel is 2mm.The flow field at 10% chord downstream from the cascade trailing edge was measured at 38 span-wise positions and 26 pitch-wise positions using a mini five-hole pressure probe. The static pressure distribution on the tip end wall is measured at 16 pitch-wise stations and 17 chord-wise stations. Results show that there exists great pressure gradient in the pressure side for the fiat tip and the pressure side squealer tip, which means strong leakage flow. The pressure gradient from the pressure side to the suction side is greatly decreased for the grooved tip, and the resulting leakage flow is weaker. The core of the leakage vortex moves closer to the suction side for the pressure side squealer tip and farther away from the suction side for the suction side squealer tip. The pressure side squealer has little advantages over the fiat tip in improving the flow capacity and reducing the overall losses. The suction side squealer tip and grooved tip can effectively decrease the intensity of the tip leakage vortex, improve the flow capacity and reduce loss of the turbine cascade passage and the grooved tip performs the best.

Geometry Effects on Aerodynamics Performance of a Low Aspect Ratio Turbine Nozzle

This paper describes the influence of some geometric parameters on aerodynamics performance of a low-aspect-ratio turbine blading designed by a novel method developed at the Institute of Engineering Thermophysics, Chinese Academy of Sciences. This is a part of the study on aerodynamics optimization of turbomachinery. It follows the development of the basic ideas in the turbomachinery aerodynamics research project at the institute. The present paper concentrates mainly on the effects of geometry, such as stagger angle, leading and trailing edge thickness, maximum thickness and its location on adiabatic efficiency, total pressure ratio and mass flow rate. The study was performed and assessed for a low-aspect ratio turbine nozzle using 3D steady Reynolds-averaged N.S. solver. Using the knowledge of the flow physics analysis an optimized turbine nozzle was obtained.

Computational Study of the Effects of Shroud Geometric Variation on Turbine Performance in a 1.5-Stage High-Loaded Turbine

Generally speaking, main flow path of gas turbine is assumed to be perfect for standard 3D computation. But in real engine, the turbine annulus geometry is not completely smooth for the presence of the shroud and associated cavity near the end wall. Besides, shroud leakage flow is one of the dominant sources of secondary flow in tur- bomachinery, which not only causes a deterioration of useful work but also a penalty on turbine efficiency. It has been found that neglect shroud leakage flow makes the computed velocity profiles and loss distribution signifi- cantly different to those measured. Even so, the influence of shroud leakage flow is seldom taken into considera- tion during the routine of turbine design due to insufficient understanding of its impact on end wall flows and tur- bine performance. In order to evaluate the impact of tip shroud geometry on turbine performance, a 3D computa- tional investigation for 1.5-stage turbine with shrouded blades was performed in this paper. The following ge- ometry parameters were varied respectively：

Parametric optimisation of two Pelton turbine runner designs using CFD

This paper aims to develop a generic optimisation method for Pelton turbine runners using computational fluid dynamics （CFD）. Two different initial runners are optimised to achieve more generic results. A simple bucket geometry based on existing bibliography is parameterised and initially optimised using fast Lagrangian solver （FLS）. It is then further optimised with a more accurate method using ANSYS Fluent. The second geometry is a current commercial geometry with good initial performance and is optimised using ANSYS CFX. The analytical results provided by CFX and Fluent simulations are used to analyse the characteristics of the flow for different runner geometries.

Design and study on variable nozzle mixed-flow turbocharger

A spatial motion mechanism was designed which could make all the nozzle vanes rotate a- round the center of ball with the same radius synchronously to realize control of the variable nozzle mixed-flow turbocharger （VN-MT）. The back and abdomen of the nozzle vane was designed as arc- shaped. A variable nozzle ring perfectly combined with the mixed-flow turbine was made available. The turbine geometric model of VN-MT was established through the computational fluid dynamics （CFD）. Compared with nozzleless mixed-flow turbine, the flow range of variable nozzle mixed-flow turbine was broadened tremendously while the peak turbine efficiency point was lower slightly. Flow field analysis in turbine stage showed that the energy was larger and the blade load of rotor was lower than loss of the VN-MT under designed condition the nozzleless mixed-flow turbocharger.

一种用于大型风电机组叶片自重载荷标定的弯矩解析方法研究

在大型风电机组的机械载荷测试中,叶片自重引起的摆振弯矩和挥舞弯矩的载荷标定精确度直接影响叶片和风轮的载荷测试效果。因此分析叶片自重在应变片测量位置的弯矩解析结果是叶片载荷标定的关键。首先,运用解析几何原理,提出了一种基于优选的三维坐标系和坐标变换的叶片自重弯矩解析方法。其次,为了消除主轴倾角对优选的三维坐标系的影响,提出了一种在优选的三维坐标系中调整叶片重力矢量方向的方法,并推导出了考虑各种影响因素下的弦摆振弯矩、弦挥舞弯矩的解析表达式。最后,在实际的叶片载荷测试项目中,应用两种标定分析方法进行对比,两种方法得到的叶片载荷测试结果具有很好的一致性和代表性。理论分析和试验结果验证了本文所提的叶片自重弯矩解析方法对叶片载荷标定的有效性和可行性。

变几何涡轮燃气轮机总体性能研究

为深入了解变几何涡轮对燃气轮机的总体性能影响机理,通过部件法对燃气轮机进行建模,然后分别改变高压涡轮、中压涡轮和动力涡轮的第一级导向器喉道面积,在不考虑导叶两端调节机构和导叶间隙等对涡轮效率影响情况下,对燃气轮机总体性能的变化情况进行了系统地分析,并得出各截面的总温与总压变化情况。结果表明:在采用保持高压涡轮入口总温恒定的控制规律时,增大燃气轮机的高压涡轮流通能力,燃气轮机输出轴功率与耗油率均不断增加,高压涡轮流通能力增加10%,输出轴功率与耗油率分别上升2.83%与1.13%;增大燃气轮机的中压涡轮流通能力,导致燃气轮机输出轴功率降低,耗油率上升,中压涡轮流通能力增加10%,输出轴功率降低9.96%,耗油率上升3.63%;动力涡轮流通能力增加,燃气轮机输出轴功率先上升,后有小幅下降,耗油率增大,动力涡轮流通能力变化量从0增加到10%,输出轴功率降低0.05%,耗油率增加2.01%。

变桨距风力发电机组恒功率反馈线性化控制

在额定风速以上时,为保证风电机组的安全稳定运行,需要降低风力机捕获风能,使风力机的转速及功率维持在额定值,基于微分几何反馈线性化方法,提出变桨距风力发电机组恒功率控制策略.建立了风力机的仿射非线性模型,采用微分几何反馈线性化变换实现全局精确线性化;根据新的线性化模型,以风力机转速为输出反馈变量,叶片桨距角为输入控制变量,设计桨距角控制器;在风速高于额定值时调节风力机维持在额定转速,从而实现额定风速以上的恒功率控制.仿真结果表明,所提控制策略能较好地解决变桨距风力发电机组额定风速以上的恒功率控制问题,控制方法具有较好的适应性和鲁棒性.

舌形挡板变截面涡轮（VGT）的研究

由模拟试验得到的舌形ＶＧＴ蜗壳内的流动模型和进出口的速度系数，为该产品的设计和结构优化提供了理论依据。在匹配试验中总结了多种效应的相互影响和渗透，提示了舌形ＶＧＴ的发展前景。

导叶间隙不确定性对可调向心涡轮影响数值研究

为了评估可调向心涡轮导流叶片叶顶及叶根间隙尺寸不确定性对涡轮级性能的影响,首先将喷嘴环叶片大开度模型的单通道定常数值结果与实验数据对比;然后以导流叶片小开度涡轮为研究对象,数值模拟导叶两端叶顶间隙尺寸多种分配模型三维流场,总结出导叶间隙不确定性与涡轮级性能之间相应变化规律;最后选取导叶两端间隙平均分配模型和最优涡轮性能下间隙分配模型开展多通道定常/非定常计算,用于分析间隙分配变化对转静干涉影响。研究结果表明:当导流叶片轮缘侧间隙尺寸占全部间隙尺寸5%~15%范围时,涡轮级效率较高;当导叶间隙全部集中在轮缘侧时,涡轮效率较低;最高、最低效率差别约为6%。间隙泄漏流变化将引起下游转子叶片进口气流角发生变化,进而改变转子叶片吸力面前缘分离涡损失大小。此外,导叶两端间隙分配变化可以改变嘴环叶片吸力面激波强度,并通过诱发交变载荷变化方式影响转子叶片可靠性。

一种考虑变几何特性的重型燃气轮机建模方法

在传统燃气轮机仿真模型的基础上,对比分析模型计算结果与机组性能试验数据,定量地得到了可转导叶(IGV)开度变化对燃气轮机性能的影响,建立了考虑IGV开度变化对机组性能影响的重型燃气轮机性能仿真模型.结果表明:所建模型的稳态计算结果与试验数据相吻合,正确反映了燃气轮机参数随燃气轮机功率的变化关系,可以应用于系统动态特性分析以及控制系统的设计和验证.

可变截面涡轮增压器与废气再循环对柴油机排放的影响

以一台重型柴油机为试验对象,研究可变截面涡轮增压器(VGT)和废气再循环(EGR)阀门开度对柴油机增压比、空燃比、燃油消耗率及NO_x,CO,HC,CO2和烟度等排放特性的影响.研究结果表明,随着EGR阀门开度的增大,增压比、空燃比降低,经济性变差.EGR阀门开度和VGT阀门开度对NO_x排放影响很大,随EGR阀门开度和VGT阀门开度增大,NO_x排放的体积分数显著降低,但HC,CO,CO2的体积分数和烟度升高.为实现降低NO_x排放的同时控制燃油消耗率和烟度的升高,可在中等负荷时选择EGR阀门开度50%、VGT阀门开度45%的控制策略;在高负荷时选择EGR阀门开度75%、VGT阀门开度55%的控制策略.

变转速风力机额定风速以上的非线性控制——恒功率输出控制问题

讨论了在额定风速以上时变转速风力机的控制问题，系统采用基于微分几何理论下的桨距角和触发角双输入控制．变转速风机是一个带有大范围风速的多输入多输出非线性系统，通过坐标变换，使非线性系统转化为一个标准的线性系统．直接利用所推导的仿射非线性机理模型，在额定风速以上，采用微分几何精确线性化理论，通过坐标转换，实现变转速风机全局精确线性化控制，给出了反馈控制算法。

液压型风力发电机组主传动系统稳速控制研究

以液压型风力发电机组定量泵-变量马达主传动系统为研究对象,建立液压主传动系统数学模型和传递函数,针对励磁同步发电机并网运行对变量马达稳速输出控制要求及系统模型中存在的相乘非线性,利用小信号线性化方法建立一种在稳定转速附近的抗干扰控制方式。分析变量马达斜盘基准折算值、马达斜盘调整机构阀控缸响应速度、不同定量泵转速阶跃对转速控制系统的影响规律,以仿真和实验验证稳速控制方法的鲁棒性。

大子午扩张变几何动力涡轮流场及损失特性分析

针对四级大子午扩张变几何动力涡轮开展数值计算研究,描述可调静叶端部间隙泄漏涡的形成过程,研究可调静叶转动前后可调静叶级三维流场结构及其损失机理的变化情况,分析静叶可调对动力涡轮各级总体性能的影响。研究结果表明:涡轮变几何引入了可调静叶端部部分间隙以及泄漏涡和通道涡的相互干扰,且泄漏涡涡核主要是由旋转轴后侧的泄漏流线组成;可调静叶转动不仅导致静叶自身出现攻角流动,还导致下游动叶前缘附近产生了大攻角分离流动,并且可调静叶关闭导致的动叶吸力侧大分离流动是由轮毂端壁附近分离泡螺旋向上运动产生,表现出强烈的三维特性,严重恶化变几何涡轮性能;可调静叶转动改变了静叶的喉部面积,导致涡轮级间焓降重新分配,从而在不同程度上影响动力涡轮各级流动性能,整体上对可调静叶级的影响最为明显。

基于CFD的贯流式水轮机叶片改型及性能研究

采用改型和CFD方法,对一贯流式水轮机转轮叶片进行改型优化。采用15条叶高方向从叶片头部到尾部的B样条曲线来对叶片进行参数化,通过调整B样条的控制参数来达到修改叶片几何形状的目的。结果表明,通过对叶片的改型优化,尾水管的水力损失明显有所降低,水轮机在最优工况和额定工况点的效率和空化性能都有所提高。同时也对优化前后的流场进行了详细的分析和比较,模型试验的结果也验证了改型和数值仿真的正确性。

微分几何在水平轴恒速风力发电机系统的应用

直接利用推导得到的仿射性非线性模型，采用微分几何精确线性化理论，实现恒速风力机全局精确线性化控制，给出了反馈控制算法。

风速波动下风电场变参数等值建模方法

为解决风速波动下利用风电场常用等值建模方法建立的风电场模型存在无功功率误差问题,提出了一种适用于定速机组风电场的变参数等值建模方法。分别针对机端固定电容器和分组投切电容器两种无功补偿方式,理论推导变参数电容的计算方法,并给出等值模型的结构及其仿真建模过程,从而得到风电场变参数模型。通过算例仿真,并与常用等值方法进行了比较分析。结果表明,提出的变参数等值建模方法是有效的,所建立的风电场等值模型能够较准确地反映风电场并网点的风速波动特性。