Local topography-induced pressure gradient effects on the wake and power output of a model wind turbine

Wind-tunnel experiments were performed to study the effect of favorable and adverse constant pressure gradients(PG)from local changes in the topography right downwind of a model wind turbine.Particle image velocimetry was used to characterize the near and intermediate wake regions.We explored five scenarios,two favorable,two adverse PG,and a case with negligible PG.Results show that the PGs induce a wake deflection and modulate the wake.They imposed a relatively small impact on the turbulence kinetic energy and kinematic shear stress but a comparatively dominant effect on the bulk flow on the flow recovery.Based on this,a simple formulation is used to describe the impact of PG on the wake.We modeled the base flow through a linearized perturbation method;the wake is obtained by solving a simplified,integrated streamwise momentum equation.This approach reasonably estimated the flow profile and PG-induced power output variations.

Nonlinear inversion-based output tracking control of a boiler-turbine unit

The capability to perform fast load-following has been an important issue in the power industry. An output tracking control system of a boiler-turbine unit is developed. The system is composed of stable inversion and feedback controller. The stable inversion is implemented as a feedforward controller to improve the load-following capability, and the feedback controller is utilized to guarantee the stability and robustness of the whole system. Loop-shaping H∞ method is used to design the feedback controller and the final controller is reduced to a multivariable PI form. The output tracking control system takes account of the multivariable, nonlinear and coupling behavior of boiler-turbine system, and the simulation tests show that the control system works well and can be widely applied.

Improved Design of a 25 MW Gas Turbine Plant Using Combined Cycle Application

This paper presents the improved design of a 25 MW gas turbine power plant at Omoku in the Niger Delta area of Nigeria, using combined cycle application. It entails retrofitting a steam bottoming plant to the existing 25 MW gas turbine plant by incorporating a heat recovery steam generator. The focus is to improve performance as well as reduction in total emission to the environment. Direct data collection was performed from the HMI monitoring screen, log books and manufacturer’s manual. Employing the application of MATLAB, the thermodynamics equations were modeled and appropriate parameters of the various components of the steam turbine power plant were determined. The results show that the combined cycle system had a total power output of 37.9 MW, made up of 25.0 MW from the gas turbine power plant and 12.9 MW (an increase of about 51%) from the steam turbine plant, having an HRSG, condenser and feed pump capacities of 42.46 MW, 29.61 MW and 1.76 MW respectively. The condenser cooling water parameters include a mass flow of 1180.42 kg/s, inlet and outlet temperatures of 29.8°C and 35.8°C respectively. The cycle efficiency of the dry mode gas turbine was 26.6% whereas, after modification, the combined cycle power plant overall efficiency is 48.8% (about 84% increases). Hence, SIEMENS steam turbine product of MODEL: SST-150 was recommended as the steam bottoming plant. Also the work reveals that a heat flow of about 42.46 MW which was otherwise being wasted in the exhaust gas of the 25 MW gas turbine power plant could be converted to 12.9 MW of electric power, thus reducing the total emission to the environment.

Asymptotic Tracking Control for Wind Turbines in Variable Speed Mode

This paper presents a variable speed control strategy for wind turbines in order to capture maximum wind power.Wind turbines are modeled as a two-mass drive-train system with generator torque control.Based on the obtained wind turbine model,variable speed control schemes are developed.Nonlinear tracking controllers are designed to achieve asymptotic tracking for a prescribed rotor speed reference signal so as to yield maximum wind power capture.Due to the difficulty of torsional angle measurement,an observer-based control scheme that uses only rotor speed information is further developed for global asymptotic output tracking.The effectiveness of the proposed control methods is illustrated by simulation results.

Studying the Role Played by Evaporative Cooler on the Performance of GE Gas Turbine Existed in Shuaiba North Electric Generator Power Plant

It’s well known that the performance of a gas turbine (efficiency, heat rate and power generated) is largely dependent on mass flow rate of air, inlet air temperature and turbine inlet temperature (TIT). As turbine inlet temperature is dependent on quantity of burned fuel so that this factor is dropped out from this paper. It’s also known that gas turbines are constant volume machines i.e. at a given shaft speed they always move the same volume of air, but the power out-put of a turbine depends on the flow of mass through it. This is precisely the reason why on hot days, when air is less dense, power output falls off. A rise of one degree Centigrade temperature of inlet air decreases the power output by 1% and at the same time heat rate of the turbine also goes up. This is a matter of great concern to power producers. Many techniques have been developed to cool the inlet air to gas turbine. Some of these techniques to decrease the inlet air temperature are discussed here. The evaporative cooling technique is taken as a case study in this paper. A comparative studying is carried out between a unit using this technique and the same unit when the evaporative cooler is idle. The results advert to an increase in power output by 11.07% and a decrease in heat rate by approximately 4% when inlet air temperature drops from 50°C to 26°C.

Influence of Additional Device on Performance of the Marine Current Turbine

To investigate the influence of additional device on the flow in marine current turbine, two additional devices for ma- rine current turbine including short diffuser and long diffuser types are studied based on the test data of original marine current turbine. The results of numerical simulation show that the additional device with flange structure, compared to marine current turbine without additional device, can obtain more output power. However, it brings the inhomogeneity of additional device force as the increasing of effective output power. At same time, due to existence of the flange, two karman vortices are found behind the flange. The low pressure region produced by additional device and flange struc- ture can speed up the flow around the marine current turbine, so as to improve the output power.

Optimal Control of Wind Turbines under Islanded Operation

In this paper, an optimal control scheme for wind turbine output torque and power regulation under the influence of wind disturbances is presented. The system considered is a dynamic mechanical-based model with pitch and generator torque actuators for controlling the pitch and generator torque. The performance of linear matrix inequality (LMI) formalism of linear quadratic regulator (LQR);linear quadratic regulator with integral action (LQRI) and model predictive control (MPC) were compared in response to a step change in wind disturbance. It is shown by Matlab simulation that the LQRI outperformed both LQR and MPC controllers.

海上单桩基础风机土体阻尼校核与预测方法研究

对长期承受动荷载作用的海上风机而言,土体阻尼是影响其疲劳寿命的重要因素之一,不同学者对其考虑方式尚未统一,同时土体阻尼的输入和校核结果间存在一定差异.针对这一问题,本文以江苏黄海某风机工程项目为依托,在ABAQUS软件中建立单桩基础式海上风机有限元计算模型,设计了包含风机结构壁厚、基础埋深、结构密度及土体阻尼等因素的系列计算方案,采用自由振动分析对土体阻尼输入与校核间差异性进行系统研究,并设计正交试验采用极差分析方法进行各因素的影响权重分析,在此基础上基于多参数非线性回归分析提出了综合拟合公式,并给出相应土体校核阻尼预测方法.结果表明:风机土体阻尼校核结果远小于其输入值,仅为后者的2%~15%;校核阻尼与风机结构壁厚、结构密度呈正相关关系,与基础埋深呈负相关关系,但当基础埋深达到8倍桩径后,则基本不再影响校核结果;以上各因素并非线性独立,三者共同作用决定土体阻尼校核结果,其中结构壁厚影响最为显著,其次为结构密度,最后为基础埋深;本文提出的以结构壁厚与校核结果间幂函数为基础的拟合经验公式,其拟合精度良好,可有效模拟各因素与校核阻尼间的关系,同时可为同类型风机土体阻尼校核预测提供数学基础.

基于燃机余热和地热能的联合发电系统优化设计及热力性能分析

设计了一种超临界二氧化碳(S-CO_(2))再压缩系统与地热双闪蒸系统相结合的新型燃机余热利用联合发电系统。基于所建联合系统参数优化模型,应用遗传算法计算分析了联合系统内部参数和边界参数对最大输出功和燃机余热利用率的影响。结果表明:通过系统参数优化,联合系统实现了余热在2个子系统中的合理分配,加深了燃机余热的进一步利用;当一级闪蒸压力取99.89 kPa、二级闪蒸压力取29.4 kPa、S-CO_(2)质量流量取22.68 kg/s、分流比取0.3085时,联合系统最大净输出功达到6.402 MW,对应余热效率为67.9%;当一级闪蒸压力在90~115 kPa、二级闪蒸压力在25~35 kPa时,联合系统均可实现较高的净输出功,与最佳值的相对偏差在0.8%以内;随着S-CO_(2)流量或分流比逐渐增大,联合系统的净输出功均呈现先增大后减小的规律;联合系统的最大净输出功随S-CO_(2)透平进口压力的增大而增加,随S-CO_(2)透平出口压力和预冷器出口温度的增大而减小。

变入口压力下大容量压缩空气储能电站空气透平动态过程及调节特性研究

压缩空气储能系统的空气透平入口压力变化较大,为了掌握该条件下透平的特性及规律,使用多学科仿真平台MSP和模块化建模工具PowerBuilder搭建了全工艺流程的300MW级压缩空气储能系统,分析空气透平在入口压力大幅变化情况下的运行特性和调节过程,揭示储气室压力大幅变化下透平膨胀比、出口温度和效率等关键参数的变化规律,确定了透平的功率调节过程及响应特性,并分析了透平入口温度对机组功率的影响和限制,为大容量压缩空气储能系统空气透平的运行和调节提供了数据支撑和科学依据。

塔影效应下风轮仰角对风力机气动特性的影响

考虑风力机塔影效应的影响,针对风轮仰角导致风力机气动特性更为复杂的问题,文章对不同仰角水平轴风力机流场进行了数值模拟,分析了风力机叶片截面压力分布、涡量以及塔筒表面压力随相位角的变化规律,探究了风轮仰角对风力机输出功率的影响。结果表明:增大风轮仰角会降低叶片表面压力,减小叶尖部分压差,使得叶片表面高涡量区域减小;添加风轮仰角会使叶片对塔筒影响减小,塔筒表面高涡量区域随着风轮仰角的增大逐渐减小,降低塔筒表面压力波动。当叶片经过塔筒时,塔影效应对风力机影响较大,风力机输出功率降低;当叶片竖直向上时,风力机输出功率达到最大。为风力机添加仰角后,随着风轮仰角的增大,风力机的输出功率与输出功率波动均呈现先增大后减小的趋势;风力机输出功率在风轮仰角为3°时最大,输出功率波动在风轮仰角为6°时最小。

双馈型风电机组传动链降载控制技术研究与仿真

为定量研究双馈型风力发电机组传动链的扭振控制,提出了一种基于卡尔曼滤波的反馈控制策略,并通过仿真计算的方式对比了传动链扭振的控制效果。以7.0 MW双馈型风力发电机组传动链为研究对象,采用卡尔曼滤波估计传动链扭振角度,并以低速轴扭振速度估计值为参考设计了发电机附加电磁转矩作用于风电机组转矩控制,与虚拟阻尼控制、无阻尼控制进行了20年全生命周期内的载荷与发电量计算对比。结果表明:经过卡尔曼滤波估计的低速轴扭角与实际值的相关性可以达到0.99;基于卡尔曼滤波的反馈控制分别与虚拟阻尼控制、无阻尼控制的关键差异为,传动链低速轴等效疲劳载荷分别降低2.11%、4.89%,传动链高速轴等效疲劳载荷分别降低1.99%、4.78%,发电量分别降低200、700 k W·h。卡尔曼滤波对传动链扭角估计较准确,且以卡尔曼滤波估计得到的低速轴扭振速度设计的附加电磁转矩对传动链扭振具有非常好的抑制效果。

考虑疲劳载荷分布的海上风电机组出力优化控制

针对海上风电场疲劳载荷分布不均衡、各机组维护频次不同步而导致运维成本高的问题,提出了一种考虑疲劳载荷分布的海上风电机组出力优化控制策略。基于风机最小推力系数控制策略有效降低风电场的尾流效应,以疲劳载荷分布均衡为目标优化各机组的疲劳载荷,使各机组维护频次同步,进而降低运维成本。仿真结果表明:与风机最大功率点跟踪控制策略相比,所提策略在实现风电场疲劳载荷均衡分布的同时,使得风电场年发电量提高4.20%。

某型燃汽轮机动力输出轴的强度分析

燃汽轮机动力输出轴具有不同于柴油机等的结构设计,且需要承受较大外载。为提高燃气轮机的可靠性、可用性以及可维护性,文章利用理论简化方法及有限元软件ANSYS对某型燃气轮机动力输出轴进行强度、刚度分析。通过分析得出,该轴结构设计满足燃气轮机工作需要,其建模及计算分析方法为履带车辆用燃汽轮机的设计提供理论依据及分析方法。

典型功率输出构型航改燃机动力学特点综述

航改燃机是指以成熟航空发动机为母型,通过改进研制形成的燃气轮机,是近年来轻型燃气轮机研制的主要手段,可使开发技术难度显著降低、研制周期大幅缩短、研发费用有效缩减。根据航改燃机功率输出形式的不同,可分为:后端输出功率构型燃机、前端输出功率构型燃机和前后同时输出功率构型燃机三类构型,对应的动力学特性设计难度和设计理念差异显著。为了总结和掌握不同输出构型燃机动力学设计特点,开展三类输出构型的结构特征、临界转速-工作转速关系和应变能分布研究。结果表明:现阶段国内外航改燃机转子系统总体上仍追求工作转速范围内刚性转子设计,即需要严格控制转子应变能量级,因此保证和提高转子刚度是航改燃机动力学设计的重点;从结构差异来看,动力学设计由易到难依次为后端输出功率构型、前端输出功率构型、前后同时输出功率构型。研究和总结不同输出功率构型航改燃机动力学特点,对在研/新研航改燃机的设计和研制具有明显的工程参考意义。

洁净与覆冰条件下风力发电机输出功率计算方法及现场试验验证

高海拔地区风能资源丰富,然而建设于此的风力发电机面临严重覆冰问题。覆冰会破坏叶片气动结构,造成输出功率损失,影响供电质量。了解不同工况下的风力发电机输出功率情况,有助于电力部门进行合理的电力调度。该文提出了一种适用于洁净和覆冰条件下的风力发电机输出功率计算方法。该方法以叶素动量理论为基础,同时引入二维计算流体动力学(CFD)仿真方法来计算叶素的升力与阻力系数。将计算结果与现场试验运行结果对比发现,该计算方法可以在工程应用允许的误差范围内获得风力发电机的输出功率。此外,通过比较基于该方法获得的关键气动参数在不同风速下沿叶片翼展方向的分布发现,冰层的存在会降低叶片对风能的利用率,减小叶片旋转扭矩,从而导致输出功率降低;并且随着风速的增加,覆冰所带来的负面影响更加明显。

串列布置不同容量风力机输出功率的数值模拟

为了研究垂直交错布置方式布置不同风力机对其输出功率的影响,本文利用OpenFOAM开源软件,使用致动线模型和RANS结合标准k-ε模型的数值方法,对采用5种布置方式的WindPACT 1.5 MW(WP 1.5 MW)风力机和两种不同轮毂高度的NREL 5 MW风力机的风电场进行研究。研究表明:将两台WP 1.5 MW风力机中的一台风力机替换为NREL5 MW风力机可有效提高风电场总输出功率。将上游风力机替换可以更大地提升风电场总输出功率,总输出功率提升了104.12%;提高NREL 5 MW风力机的轮毂中心高度,形成垂直交错风电场时可以增加上下游风力机的输出功率,进而能够更好地利用垂直方向上的风资源。将下游NREL 5 MW风力机轮毂中心高度提升0.5D能更大程度提升风电场的总输出功率,总输出功率提升了132.79%。

旋转作用下水平轴风力机气动性能分析

为研究水平轴风力机在大气边界层近地面非定常来流作用下气动耦合特性,建立了基于剪切应力传输(shear stress transfer,SST)湍流模型的计算流体力学(computational fluid dynamics,CFD)模型和静力结构模型。为模拟风轮在近地面的气动状态,通过单向流固耦合方法对流场均匀入流风速和旋转效应作用下不同工况进行数值耦合计算,求解风力机流场中的速度场、压力场、结构响应状态以及输出功率,分析对比流场不同方向风力机周围速度变化、表面压力分布、结构应力应变规律、整体变形情况和功率变化。结果表明:在均匀来流和旋转共同作用下,流速和压力主要沿风轮径向变化,沿叶片展向至叶尖速度逐渐增大;整机结构附近有明显的气流扰动变化;停机工况和旋转工况(考虑旋转效应)塔影效应干扰下叶片变形在上下风区波动较大;入流风速大小对风力机输出功率有显著影响。

基于多自由度运动条件下风力机动力学特性研究

该文提出耦合无规则、多自由度旋转运动的风力机试验方案,通过物理模型试验,研究风电场阵列布置、不同风力机轴向间距工况下,各排风力机来流速度、功率及其波动特性。结合功率时间尺度积分的概念,探究其与风力机平均输出功率的关系,并建立预测功率波动特征的数学模型。研究结果表明:风力机的来流速度有大尺度、低频率和小尺度、高频率的信号特征,从功率时间尺度积分的趋势可看出,处于下游的风力机,功率波动逐渐增加。由功率能谱特性曲线可知功率波动的能量随着频率的增大而衰减,在低频率段衰减曲线近似f-2的变化规律;在高频率段,能谱特性曲线近似f-5/3-2的变化规律。

风向变化速度对风力机功率及转速的影响

为了探索风向变化时风力机输出功率及转速的变化情况,以某S翼型三叶片水平轴风力机为研究对象,利用旋转平台模拟风向匀速变化过程,采用IEC61400中规定的极端风向角变化速度5°/s为上限,每间隔1°/s选取1个风向变化速度,即选取1°/s, 2°/s, 3°/s, 4°/s和5°/s这5个风向变化速度,研究不同风向变化速度下风力机输出功率、转速的变化规律.结果表明:风力机在不同风向变化速度下其输出功率与转速总体都呈现波动下降趋势,同一风速下风向变化速度越大,下降速率越快,但在其风向变化过程中对应的下降幅值越小;在风向变化开始与结束时都存在迟滞现象,风向变化开始时风力机输出功率出现小幅度上升,并持续波动3 s左右后才会开始下降;风向变化结束后,风力机需要继续运行一段时间后输出功率与转速才会达到稳定值,风向变化速度越大,该迟滞时间越长,初始尖速比越大,最终稳定后数值越大.