Numerical Modelling of the Aeroelastic Behaviour and Variable Loads for the Turbine Stage in 3D Transonic Flow

Introduction Aeroelastic phenomena in the turbine stage are characterized by instability, continuous interaction and energy exchange between the fluid and the structure; so they cannot be studied properly in the frame of each of uncoupled domains separately (aerodynamics or structural dynamics). The traditional approach in flutter calculations of bladed disks is based on frequency domain analysis[1,2], in which the blade motion is assumed to be a harmonic function of time with a constant phas…     

Numerical Analysis of the Aeroelastic Behaviour for the Last Turbine Stage in 3D Transonic Flow

An understanding of the physics of the mutual interaction between gas flow and oscillating blades, and the development of predictive capabilities is essential for improving overall efficiency, durability and reliability. In this study presented the algorithm proposed involving the coupled solution of 3D unsteady flow through a turbine stage and dynamic problem for rotor blades motion by action of aerodynamic forces without separating outer and inner flow fluctuations. There has been performed the calculations for the last stage of the steam turbine under design and off-design regimes. It has investigated the mutual influence of both outer flow non-uniformity and blades oscillations. It has shown that amplitude-frequency spectrum of blade oscillations contains the high frequency harmonics, corresponding to rotor moving one stator blade pitch, and low frequency harmonics caused by blade oscillations and flow non-uniformity downstream from the blade row.     

Flap/lead–lag aeroelastic stability of wind turbine blade sections

The scope of this article is to investigate the aeroelastic stability of wind turbine blade sections subjected to combined flap/lead–lag motion. The work is motivated by recent concern about destructive ‘edgewise' vibrations of modern, half‐megawatt‐scale, blades. The aeroelastic governing equations derive from the combination of a spring–mass–damper equivalent of the structure and a ‘non‐stationary' aerodynamic model. The aerodynamic model used in the present context is the differential dynamic stall model developed at ONERA. The resulting equations of motion are linearized and their stability characteristics are investigated in terms of the system entries, expressed through suitable, non‐dimensional, structural and aerodynamic parameters. Copyright © 1999 John Wiley & Sons, Ltd.     

风力机叶片动态气弹变形及其对整机性能的影响

基于风力机整机刚柔耦合模型,文章提出了一种叶片动态气弹扭转变形分析的新方法。该方法采用SIMPACK和AeroDyn软件联合数值仿真对风力机在几种恶劣风况下进行动力学分析,通过对分析结果的变换处理,进而得到叶片在复杂工况下的动态气弹变形数据。采用该方法,重点分析了叶片气弹扭转变形对风力机气动功率及气弹稳定性的影响。该方法为大型风电叶片的气弹特性评价以及气弹剪裁设计提供了一种新的技术手段。     

Effect of steady deflections on the aeroelastic stability of a turbine blade

This paper deals with effects of geometric non‐linearities on the aeroelastic stability of a steady‐state deflected blade. Today, wind turbine blades are long and slender structures that can have a considerable steady‐state deflection which affects the dynamic behaviour of the blade. The flapwise blade deflection causes the edgewise blade motion to couple to torsional blade motion and thereby to the aerodynamics through the angle of attack. The analysis shows that in the worst case for this particular blade, the edgewise damping can be decreased by half. Copyright © 2010 John Wiley & Sons, Ltd.     

Fluid flow characteristics and convective heat transfer improvement on a gas turbine blade

The flow field features and heat transfer enhancement are investigated on a gas turbine blade by applying the jet impingement cooling method. The distribution of the flow field and the Nusselt number (Nu) was determined on the targeted surface in the cooling channel. The injection holes of different shapes, such as circular, square, and rectangular were considered. The Reynolds numbers (Re) of the airflow in the range of 2000–5000 and aspect ratios of 0.5–2 were particularly focused. The flow vortices and recirculation in the cooling channel and their influence on the heat transfer enhancement were analyzed in detail under different airflow and geometric conditions. Decreasing the ratio of the distance between jet-to-target plate to the diameter of the jet orifice (H/d) increased the heat transfer rate and produced high-intensity vortices and recirculation zones. It was noticed that the formation and generation of vortices and recirculation have important effects on the convective heat transfer rate at the impingement surface. Local Nusselt number, formation of complex vortices, and airflow recirculation in the cooling channel decreased with the increase in the distance between the jet hole and the targeted surface. It was found that with the increase in the Reynolds number of the jet, heat transfer between cold airflow and the targeted surface increased. Moreover, it was observed that the cooling performance of the round and square jet holes was better than the rectangular holes.     

Simulation of 3D flow in turbine blade rows including the effects of coolant ejection

This paper describes the numerical simulation of three-dimensional viscous flows in fir-cooled turbine blade rows with the effects of coolant ejection. A TVD Navier-Stokes flow solver incorporated with Baldwin-Lomax turbulence model and multi-grid convergence acceleration algorithm are used for the simulation. The influences of coolant ejection on the main flow are accounted by volumetric coolant source terms. Numerical results for a four-stage turbine are presented and discussed.     

Blade parameterization and aerodynamic design optimization for a 3D transonic compressor rotor

The present paper describes an optimization methodology for aerodynamic design of turbomachinery combinedwith a rapid 3D blade and grid generator(RAPID3DGRID),a N.S.solver,a blade parameterization method(BPM),a gradient-based parameterization-analyzing method(GPAM),a response surface method(RSM)withzooming algorithm and a simple gradient method.By the use of blade parameterization method a transonic com-pressor rotor can be expressed by a set of polynomials,and then it enables us to transform coordinate-expressedblade data to parameter-expressed and then to reduce the number of parameters.With changing any one of theparameters and by applying grid generator and N.S.solver,we can obtain several groups of samples.Here onlyten parameters were considered to search an optimized compressor rotor.As a result of optimization,the adiabaticefficiency was increased by 1.73%.     

Aero-elastic behavior of a flexible blade for wind turbine application: A 2D computational study

This paper presents a computational study into the static aeroelastic response of a 2D wind turbine airfoil under varying wind conditions. An efficient and accurate code that couples the X-Foil software for computation of airfoil aerodynamics and the MATLAB PDE toolbox for computation of the airfoil deformation is developed for the aero-elastic computations. The code is validated qualitatively against computational results in literature. The impact of a flexibility of the airfoil is studied for a range of design parameters including the free stream velocity, pitch angle, airfoil thickness, and airfoil camber. Static aero-elastic effects have the potential to improve lift and the lift over drag ratio at off-design wind speed conditions. Flexibility delays stall to a large pitch angle, increasing the operating range of a flexible blade airfoil. With increased thickness the airfoil deformation decrease only linearly.     

涡轮叶片蜂巢式冷却结构减阻能力数值研究

先进航空发动机中高耐温能力涡轮叶片通常要以增加冷却系统的流动阻力来提高冷却效果,但由此导致的二次流系统损失增大可能会引起整机性能的下降。为解决该问题,研究了先进涡轮叶片中典型层板冷却结构的内部流动损失产生机理,并针对性地提出两种(进/出气孔平行式和交叉式)低流动阻力的类蜂巢式冷却结构。基于三维数值仿真方法研究了其流动特点和损失特性,并揭示了该结构可以显著减小通道内气流转折角度、抑制旋涡产生和避免多股气流对撞的减阻强化机理。通过与典型层板结构的对比分析,初步验证了在相同的结构无量纲参数和流量下,两类蜂巢式冷却结构的总压损失分别可降低65~66%和67~69%,在高推重比航空发动机涡轮叶片冷却设计上具有较好的应用前景。     

透平叶顶气膜冷却效果数值研究

采用三维数值模拟方法,研究了GE E3发动机第一级透平动叶叶顶间隙内的气膜流动与换热特性,评估了气膜吹风比M分别为0.5、1.0和1.5时,对叶顶换热系数以及冷却效率的影响.计算结果表明:叶顶气膜冷却空气改变了叶顶泄漏流动特性,随着吹风比的增加,叶顶间隙内的泄漏流动区域不断缩小,从而导致叶顶间隙泄漏量不断减小;随着气膜冷却吹风比的增大,叶顶平均换热系数逐步降低;在M=1时,冷却效果最佳.     

Influence of internal channel geometry of gas turbine blade on flow structure and heat transfer

This paper presents the study of the influence of channel geometry on the flow structure and heat transfer,and also their correlations on all the walls of a radial cooling passage model of a gas turbine blade.The investigations focus on the heat transfer and aerodynamic measurements in the channel,which is an accurate representation of the configuration used in aeroengines.Correlations for the heat transfer coefficient and the pressure drop used in the design of internal cooling passages are often developed from simplified models.It is important to note that real engine passages do not have perfect rectangular cross sections,but include a comer fillets,ribs with fillet radii and a special orientation.Therefore,this work provides detailed fluid flow and heat transfer data for a model of radial cooling geometry which has very realistic features.     

Fluid structure interaction of a morphed wind turbine blade

One serious challenge of energy systems design, wind turbines in particular, is the need to match the system operation to the variable load. This is so because system efficiency drops at off‐design load. One strategy to address this challenge for wind turbine blades and obtain a more consistent efficiency over a wide load range, is varying the blade geometry. Predictable morphing of wind turbine blade in reaction to wind load conditions has been introduced recently. The concept, derived from fish locomotion, also has similarities to spoilers and ailerons, known to reduce flow separation and improve performance using passive changes in blade geometry. In this work, we employ a fully coupled technique on CFD and FEM models to introduce continuous morphing to desired and predetermined blade design geometry, the NACA 4412 profile, which is commonly used in wind turbine applications. Then, we assess the aerodynamic behavior of a morphing wind turbine airfoil using a two‐dimensional computation. The work is focused on assessing aerodynamic forces based on trailing edge deflection, wind speed, and material elasticity, that is, Young's modulus. The computational results suggest that the morphing blade has superior part‐load efficiency over the rigid NACA blade. Copyright © 2013 John Wiley & Sons, Ltd.     

Numerical simulation of tip leakage vortex effect on hydrogen-combustion flow around 3D turbine blade

In these years, a lot of environmental problems such as air pollution and exhaustion of fossil fuels have been discussed intensively. In our laboratory, a hydrogen-fueled propulsion system has been researched as an alternative to conventional systems. A hydrogen-fueled propulsion system is expected to have higher power, lighter weight and lower emissions. However, for the practical use, there exist many problems that must be overcome. Considering these backgrounds, jet engines with hydrogen-fueled combustion within a turbine blade passage have been studied. Although some studies have been made on injecting and burning hydrogen fuel from a stator surface, little is known about the interaction between a tip leakage vortex near the suction side of a rotor tip and hydrogen-fueled combustion. The purpose of this study is to clarify the influence of the tip leakage vortex on the characteristics of the 3-dimensional flow field with hydrogen-fueled combustion within a turbine blade passage. Reynolds-averaged compressible Navier-Stokes equations are solved with incorporating a k-ε turbulence and a reduced chemical mechanism models. Using the computational results, the 3-dimensional turbulent flow field with chemical reactions is numerically visualized, and the three-dimensional turbulent flow fields with hydrogen combustion and the structure of the tip leakage vortex are investigated.     

The impact of yaw error on aeroelastic characteristics of a horizontal axis wind turbine blade

Horizontal axis wind turbines operate under yawed conditions for a considerable period of time due to the power control mechanism or sudden changes in the wind direction. This in turn can alter the dynamic characteristics of a turbine blade because the flow over the rotor plane may trigger complicated induced velocity patterns. In this study, an aeroelastic analysis under yawed flow conditions is carried out to investigate the effects of yaw error on the blade behaviors and dynamic stability. A beam model including geometric nonlinearity coupled with unsteady aerodynamics based on a free-vortex wake method with the blade element theory is employed in the present study. The aerodynamic approach for a horizontal axis wind turbine blade under yawed flow conditions is verified through comparison with measurements. It is also shown that the present method gives slightly better results at high yaw angles than does the method previously published in the literature. The dynamic instabilities of a National Renewable Energy Laboratory 5 MW reference wind turbine have subsequently been investigated for various wind speeds and yaw angles. Observations are made that yaw effects induce considerable changes in airloads and blade structural behavior. Also, the aeroelastic damping values for this particular blade under yawed flow conditions can be reduced by up to approximately 33% in the worst case. Therefore, it is concluded that the impacts of yaw misalignments adversely influenced the dynamic aeroelastic stability of the horizontal axis wind turbine blade.     

Investigation of the compressible flow through the tip-section turbine blade cascade with supersonic inlet

The contribution deals with the experimental and numerical investigation of compressible flow through the tip-section turbine blade cascade with the blade 54″ long. Experimental investigations by means of optical(interferometry and schlieren method) and pneumatic measurements provide more information about the behaviour and nature of basic phenomena occurring in the profile cascade flow field. The numerical simulation was carried out by means of the EARSM turbulence model according to Hellsten [5] completed by the bypass transition model with the algebraic equation for the intermittency coefficient proposed by Straka and P?íhoda [6] and implemented into the in-house numerical code. The investigation was focused particularly on the effect of shock waves on the shear layer development including the laminar/turbulent transition. Interactions of shock waves with shear layers on both sides of the blade result usually in the transition in attached and/ or separated flow and so to the considerable impact to the flow structure and energy losses in the blade cascade.     

Bend‐bend‐twist vibrations of a wind turbine blade

Dynamics of a wind turbine blade under bend‐bend‐twist coupled vibrations is investigated. The potential and kinetic energy expressions for a straight nonuniform blade are written in terms of beam parameters. Then, the energies are expressed in terms of modal coordinates by using the assumed mode method, and the equations of motion are found by applying Lagrange's formula. The bend‐bend‐twist equations are coupled with each other and have stiffness variations due to centrifugal effects and gravitational parametric terms, which vary cyclicly with the hub angle. To determine the natural frequencies and mode shapes of the system, a modal analysis is applied on the linearized coupled equations of constant angle snapshots of a blade with effects of constant speed rotation. Lower modes of the coupled bend‐bend‐twist model are dominantly in‐plane or out‐of‐plane modes. To investigate the parametric effects, several blade models are analyzed at different angular positions. The stiffness terms involving centrifugal and gravitational effects can be significant for long blades. To further see the effect of blade length on relative parametric stiffness change, the blade models are scaled in size and analyzed at constant rotational speeds, at horizontal and vertical orientations. These studies show that the parametric stiffness effects should be taken into account when designing long blades.     

Efficient meshing of a wind turbine blade using force adaptive mesh sizing functions

This paper describes mesh sizing functions for discretization of a wind turbine blade as a shell structure. Two different functions, one along the blade span and the other chord-wise, are presented. The effect of the magnitude of the aerodynamic force has been considered in a span-wise mesh sizing function to obtain a force-adaptive mesh generator, applicable when the blade needs to be analysed as a part of an aero-structure problem. The direction of the aerodynamic force has been considered in the chord-wise mesh sizing function to improve the mesh efficiency. Results show a large improvement in the rate of convergence when the direction of the external force contributes towards the chord-wise mesh size.     

Analytical study of two-phase flow pressure-drop oscillations in a vertical heated tube

This paper focuses on an analytical investigation of two-phase flow pressure-drop oscillations in a vertical heated tube with the two-fluid model employed in the computer code MINI-TRAC. Pressure-drop oscillation is an important phenomenon appearing in a two-phase flow channel with compressible volume existing in the upstream region. In a previous investigation, pressure-drop oscillations with superimposed density-wave oscillations were observed. In this work, numerical calculations have been carried out to predict the characteristics of pressure-drop oscillations and the range of instabilities. We also offer an application of the two-fluid model to the analysis of pressure-drop oscillations at low pressure in a heated channel with a small inner diameter. Good agreement between the simulations and experiments was obtained. © 1999 Scripta Technica, Heat Trans Jpn Res, 27(8): 597–608, 1998     

Influence of blade rotation on the lightning stroke characteristic of a wind turbine

The blades of a wind turbine rotate during normal operation. To investigate the influence of blade rotation on the lightning‐attracting ability of a wind turbine, a discharge test platform is designed for scaled wind turbines. The 50% impulse voltages and flash probabilities of the scaled wind turbines with gap distances of 1 to 8 m in the static and rotary conditions are determined by using the discharge test and selective discharge test. The discharge test for a single wind turbine with a gap of 1 to 2 m indicates that the breakdown voltages of the gap between the scaled turbine and electrodes increases with an increase in the blade rotation speed. However, the discharge test with a gap distance of 4 to 8 m indicates that the breakdown voltage of the fan decreases with an increase in the blade rotation speed. The test results of the scaled dual wind turbines experiment have the same rules. To explain this phenomenon, the influence of wind speed on the space‐charge distribution and electrical field intensity of corona discharge is simulated in the background of a target thundercloud. The rotation of the fan reduces the space‐charge density near the area of the blade tip, which leads to an increase in the field strength near the blade tip of the wind turbine and a decrease in the field strength away from the blade tip. This influence varies in short and long air gap, resulting in opposite relationships between discharge voltage and distance from the tip of the turbine. The results can provide a reference for the lightning protection of wind turbines.