Heat transfer prediction on transonic turbine blades

The design and optimization of turbine blades submitted to high-temperature flows require the prediction of aerodynamic and thermal flow characteristics. A computation method for aerothermal viscous flows has been developed. The method is based on a compressible boundary layer approach. Tests were performed on turbine blade configurations. These tests include most difficulties that can be encountered in reality: laminar-turbulent transition, separation bubbles, strong accelerations, shock waves. Predictions of the wall heat transfer prove to be satisfactory.     

Interferometric fibre sensors for measurement of surface heat transfer rates on turbine blades

We describe a prototype sensor for surface heat transfer measurements based on a miniature fibre Fabry-Perot (FFP) interferometer. These sensors are being developed for a particular application where heat transfer data are currently obtained using conventional platinum thin film resistance thermometers. The specification that the sensors must exceed is: (i) temperature resolution of 25 mK over a 50 K range; (ii) temporal response of 10 μs; (iii) an ability to operate as a calorimetric heat transfer gauge.The sensor consists of a short length of single mode optical fibre (3 mm) to which low reflectivity coatings have been applied at each end. It is illuminated and interrogated by an arbitrary length of addressing fibre. A laser diode is used as the source and we have exploited the facility to frequency modulate the diode in a novel signal processing scheme.To determine the performance of the sensor, short duration heat pulses derived from a pulsed Nd: YAG laser were applied to one end of the FFP. The response time was found to be 8 μs and the sensor operation as a calorimeter was verified.     

A model for the characterization of friction contacts in turbine blades

Stresses produced by the forced vibrations can lead to a significant reduction of the life of turbo engine blades. To predict the vibration amplitudes of this components an accurate dynamic analysis is necessary. The forced response calculation of these dynamic systems is strongly affected by the presence of the contact interfaces (i.e., underplatform dampers, shrouds, root joints). Different contact models are available in literature. These models make use of contact parameters, contact stiffness and friction coefficient to evaluate the damping and stiffness related to the contact interfaces. In this paper a model is proposed to characterize friction contact of non-spherical contact geometries obeying the Coulomb friction law with constant friction coefficient and constant normal load. The hysteresis curves of the oscillating tangential contact forces vs. relative tangential displacements and the dissipated energy at the contact are obtained for different contact geometries. The developed model is suitable to be implemented in numerical solvers for the calculation of the forced response of turbine blades with embedded friction contacts.     

Very-High-Cycle-Fatigue of in-service air-engine blades, compressor and turbine

In-service Very-High-Cycle-Fatigue(VHCF)regime of compressor vane and turbine rotor blades of the Al-based alloy VD-17and superalloy GS6K,respectively,was considered.Surface crack origination occurred at the lifetime more than 1500 hours for vanes and after 550 hours for turbine blades.Performed fractographic investigations have shown that subsurface crack origination in vanes took place inspite of corrosion pittings on the blade surface.This material behavior reflected lifetime limit that was reached by the criterion VHCF.In superalloy GS6K subsurface fatigue cracking took place with the appearance of flat facet.This phenomenon was discussed and compared with specimens cracking of the same superalloy but prepared by the powder technology.In turbine blades VHCF regime appeared because of resonance of blades under the influenced gas stream.Both cases of compressor-vanes and turbine blades in-service cracking were discussed with crack growth period and stress equivalent estimations.Recommendations to continue aircrafts airworthiness were made for in-service blades.     

低A声级贯流风机叶片周向角不等距优化设计

叶轮产生离散噪声的原因是叶片间周向夹角均匀布置,因此降低叶轮离散噪声的有效手段就是破坏叶片周向夹角的均匀布置,通过合理布置各叶片夹角降低叶轮离散噪声。本文提出了采用叶片周向角不等距布置降低叶轮总离散噪声A声级的一种优化设计模型,模型充分考虑了A计权函数与波动力对脉动流场响应参数Sc乘积有关的综合衰减曲线的高低频段衰减较大的特性和人可听域频率范围在20-2000Hz之间的特点,通过算例验证采用该模型可以降低总离散噪声A声级。     

风力机叶片气动噪声的影响参数

随着风力机的大型化发展,风电机组噪声对环境的影响不容忽视,必须对风力机气动噪声进行预测和控制。选取基于NACA、DU翼型的某风力机叶片作为研究对象,采用修正BPM半经验模型计算叶片的气动噪声特性,通过改变翼型族、弦长、机组运行状态、风切变指数、来流风向参数,研究叶片外形几何参数、机组运行工况对叶片气动噪声源的影响。计算结果从多个角度总结出水平轴风力机叶片气动噪声的变化规律,为开发高效低噪风电叶片提供参考。     

Remote monitoring of ice loading on wind turbine blades based on total internal reflection

The paper presents an optical method for monitoring of transparent icing, which is applicable for remote monitoring of wind turbine blade icing. The method is based on the effect of total internal reflection of light. A point light source is formed on a wind turbine blade. When icing appears on the blade, a light circle is formed around the light source at the ice–air interface as a result of refraction and reflection of light beams; the observed size of the beam depends on the icing thickness. Using several light sources, the method enables field monitoring of icing on the wind turbine blades.     

Investigation of delta-doped quantum wells for power FET applications

We report the use of strain-balanced quantum-well structures to generate high carrier density, high mobility layers suitable for power field effect transistor (FET) applications. Standard designs of modulation-doped heterojunctions have a sheet carrier density limited to a maximum of ∼3 ×  10¹²cm⁻², while doped channel devices allow higher densities, but with degraded mobility. By combining the technique of delta-doping with the use of a compositionally graded InGaAs quantum well, grown strain balanced on InP, high mobilities and excellent saturation drift velocities have been obtained for sheet densities of 4–5 ×  10¹²cm⁻². This paper describes the structure and electrical properties of the layers and assesses their potential for FETs.     

Cable connected active tuned mass dampers for control of in-plane vibrations of wind turbine blades

In-plane vibrations of wind turbine blades are of concern in modern multi-megawatt wind turbines. Today?s turbines with capacities of up to 7.5 MW have very large, flexible blades. As blades have grown longer the increasing flexibility has led to vibration problems. Vibration of blades can reduce the power produced by the turbine and decrease the fatigue life of the turbine. In this paper a new active control strategy is designed and implemented to control the in-plane vibration of large wind turbine blades which in general is not aerodynamically damped. A cable connected active tuned mass damper (CCATMD) system is proposed for the mitigation of in-plane blade vibration. An Euler–Lagrangian wind turbine model based on energy formulation has been developed for this purpose which considers the structural dynamics of the system and the interaction between in-plane and out-of-plane vibrations and also the interaction between the blades and the tower including the CCATMDs. The CCATMDs are located inside the blades and are controlled by an LQR controller. The turbine is subject to turbulent aerodynamic loading simulated using a modification to the classic Blade Element Momentum (BEM) theory with turbulence generated from rotationally sampled spectra. The turbine is also subject to gravity loading. The effect of centrifugal stiffening of the rotating blades has also been considered. Results show that the use of the proposed new active control scheme significantly reduces the in-plane vibration of large, flexible wind turbine blades.     

逆升压式吊舱涡轮冷却器动力涡轮变工况特性研究

随着现代战机电子战能力的提升,电子吊舱设备发热功率日益增大,采用冲压空气作为冷源的逆升压式电子吊舱环控系统能够为机载吊舱提供充足的冷量。具有膨胀涡轮、动力涡轮、压缩涡轮的涡轮冷却器是逆升压式环控系统的核心部件。针对一种应用于机载电子吊舱的逆升压式空气循环系统进行了关键部件的匹配性能研究,通过改变动力轮进口压力来调节膨胀轮出口温度、压力、流量等参数,实现对环控系统的制冷量的控制,获得动力轮进口压力变化对环控系统性能的影响规律。     

A numerical procedure to design internal cooling of gas turbine stator blades

The continuing need to improve both the efficiency and the specific power of gas turbines requires to progressively increase the temperatures of the turbine inlet.Because the first stator blades are heavily thermally loaded, efficient blade cooling is necessary.The cooling system is particularly delicate and its design must follow these guidelines:

• •minimum thermodynamic and fluid dynamic losses;
• •limited blade temperature even for reduced cooling mass flow.

Although the problem is important, analyses of possible designs are not common in literature and many constructors refer to practical experience and to various experimental results.This paper presents a comparative investigation to determine the effects of internal and external cooling in the same blade, on the basis of different combined solutions as it often happens. The cooling model will be considered one-dimensional: the limitation in the accuracy of the results is by far overcome by the simplicity and versatility of the approach. Finally, practical hints for designing an effective cooling system are derived, with particular attention to impingement. Then, global cooling parameters and medium blade will be determined in off-design condition.     

Holographic window for solar power generation

A new photovoltaic generation unit based on the application of holographic technologies called a Holo-Window is proposed in this work. The basic principle and the optical configuration used for the basic experimental unit are described. Suitable fabrication technology for a hologram with the broadband spectrum required to provide the appropriate sunlight capture capability is then discussed. Finally, a laboratory-prototype Holo-Window unit was developed and its performance was evaluated.     

风力发电实验仪

研制了风力发电实验仪,并利用该实验仪探究了风速、风机转速、发电机输出电动势之间关系,测量了风机的风能利用系数,展示了风力发电涉及的工程技术问题,即:在额定风速之下,采用追踪最佳叶尖速比的调节方法可最大限度利用风能;当风速超过额定风速,用变浆距调节方法可实现风力发电平稳输出.     

Mitigation of edgewise vibrations in wind turbine blades by means of roller dampers

Edgewise vibrations in wind turbine blades are lightly damped, and large amplitude vibrations induced by the turbulence may significantly shorten the fatigue life of the blade. This paper investigates the performance of roller dampers for mitigation of edgewise vibrations in rotating wind turbine blades. Normally, the centrifugal acceleration of the rotating blade can reach to a magnitude of 7–8g, which makes it possible to use this kind of damper with a relatively small mass ratio for suppressing edgewise vibrations effectively. The parameters of the damper to be optimized are the mass ratio, the frequency ratio, the coefficient of rolling friction and the position of the damper in the blade. The optimization of these parameters has been carried out on a reduced 2-DOF nonlinear model of the rotating wind turbine blade equipped with a roller damper in terms of a ball or a cylinder, ignoring the coupling with other degrees of freedom of the wind turbine. The edgewise modal loading on the blade has been calculated from a more sophisticated 13-DOF aeroelastic wind turbine model with due consideration to the indicated couplings, the turbulence and the aerodynamic damping. Various turbulence intensities and mean wind speeds have been considered to evaluate the effectiveness of the roller damper in reducing edgewise vibrations when the working conditions of the wind turbine are changed. Further, the optimized roller damper is incorporated into the 13-DOF wind turbine model to verify the application of the decoupled optimization. The results indicate that the proposed damper can effectively improve the structural response of wind turbine blades.     

Surface laser alloying of 17-4PH stainless steel steam turbine blades

As a known high-quality precipitation hardening stainless steel with high strength, high antifatigue, excellent corrosion resistance and good weldability, 17-4PH has been widely used to produce steam turbine blades. However, under the impact of high-speed steam and water droplets, the blades are prone to cavitation, which could lead to lower efficiency, shorter life time, and even accidents. In this article, the 17-4PH blade's surface was alloyed using a high power CO₂ laser. The microstructure and microhardness of hardened 17-4PH were tested by scanning electronic microscope (SEM), X-ray diffraction (XRD), energy disperse spectroscopy (EDS) and a microhardness tester. After laser alloying, the surface layer was denser and the grain refined, while the microhardness of the surface (average 610HV_0.2) was about one times higher than that of the substrate material (330HV_0.2). The friction coefficient of the laser-alloyed 17-4PH layer was much lower than that of the substrate.