Experimental-numerical investigation of the dynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow. Part 2. Cross aerodynamic characteristics

We consider the results of investigation of cross aerodynamic characteristics of compressor blades and their dynamic stability under flexural-torsional vibrations for the cases of attached and separated flows in broad ranges of variations of the phase shift, the ratio of amplitudes of the translational and angular components of displacements, the angle of attack, the reduced frequency of vibrations, and the geometry of the blade cascade. Translated from Problemy Prochnosti, No. 4, pp. 89–100, July–August, 2009.     

车用交流发电机气动噪声试验研究

针对某型汽车交流发电机在高速段（6 000 r/min以上）噪声源以及各主要阶次对总噪声的贡献量问题,对交流发电机进行噪声测试分析。通过阶次分析得出气动噪声的频率特性,采用交流发电机有无前、后扇叶分别单独运转等试验方法确定各阶次噪声的具体来源以及前后扇叶对主要单阶次贡献量的大小。得到前后扇叶为该型交流发电机的气动噪声声源,第6、8、10、12、18等阶次为该型交流发电机的主要气动噪声成分;前扇叶对12、18阶次噪声贡献明显比后扇叶大,后扇叶对6、8、10阶次噪声的贡献较前扇叶大。该方法对汽车交流发电机的气动性能和高转速下噪声的改进提供一种切实可行的依据。     

Aerodynamic experimental investigation using stereolithography fabricated test models: the case of a linear compressor blading cascade

The purpose of this work is to demonstrate that rapid prototyping can be effectively applied for fabricating test models to be used in aerodynamic experimental investigations. The present work, in particular, concerns a linear cascade of 2½-D blades, with NACA 65-12(A10)10 profile section. Each one of the nine separate (identical) blades of the cascade has been fabricated using a stereolithography rapid prototyping technique. The cascade has been installed in an aerodynamic test rig, in order to simulate the flow conditions through a compressor blading. Aspects concerning the fabrication of the test models/blades, their functionality, their post-processing, the mounting arrangement and the pressure tubing and ports are discussed in detail. Experimental results for the distribution of the blade surface airflow pressure for various incidence angles compare favourably with computational results obtained with a panel inviscid flow numerical scheme. This implicitly indicates the effectiveness of employing stereolithography for fabricating wind tunnel test models.     

Control of the aerodynamic characteristics of wing airfoils by nonstationary energy supply in transonic flow

The possibility of controlling the aerodynamic characteristics of wing airfoils in transonic regimes of flight using one-sided pulse-periodic energy supply has been studied. The flow structure near the symmetric airfoil at different angles of attack and its aerodynamic characteristics as functions of the value of energy in its nonsymmetric (about the airfoil) supply have been determined by numerical solution of two-dimensional nonstationary gasdynamic equations. A comparison of the obtained results and the data of calculation of flow past the airfoil at different angles of attack without energy supply has been made. It has been established that a prescribed lift can be obtained, using energy supply, with a much higher fineness ratio of the airfoil than that in the case of flow past it at an angle of attack. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 1, pp. 18–22, January–February, 2009.     

Experimental-numerical investigation of the dynamic stability of flexural-torsional vibrations of compressor blades under conditions of attached and separated flow. part 3. mutual aerodynamic couplings

The paper considers the results of a study of mutual aerodynamic couplings which give rise to nonstationary aerodynamic interactions between the translational and angular components displacements of neighboring ring blades in the case of variation of attack angle, reduced vibration frequency and the geometric parameters of the blade cascade. The effect of mutual aerodynamic couplings between neighboring blades on the aerodynamic stability of flexural-torsional vibrations of the blades of the peripheral section of the shrouded fan blade ring of gas turbine engine for an attack angle of 15° has been estimated.     

Characteristics of a typical lifting symmetric supercritical airfoil

The theoretical aerodynamic characteristics of a typical lifting symmetric supercritical airfoil demonstrating its superiority over thenaca 0012 airfoil from which it was derived are presented in this paper. Further, limited experimental results confirming the theoretical inference are also presented. Invited Lecture given at the 3rd Asian Congress on Fluid Mechanics, held in Tokyo during 1–5 September, 1986     

The effect of crystallographic orientation on the natural vibration spectrum and fatigue limit of turbine rotor blades made of monocrystalline materials

Based on 3D models of rotor blades made of monocrystalline materils, the influence of crystallographic orientation of material axes on the formation of natural frequency spectrum and mode shapes of the blades has been clarified. A computational-experimental method is proposed for the evaluation of fatigue limit of monocrystalline blades, which significantly reduces the test scope while improving the reliability of test results. __________ Translated from Problemy Prochnosti, No. 5, pp. 15–27, September–October, 2008.     

Experimental-Calculation Determination of Dynamic Stability of Blade Assemblies of GTE Compressor Rotor Wheels

We discuss approaches to airfoil-cascade-based simulation of unsteady aerodynamic loads that act on the blades during their vibration in a gas flow. This paper describes the main concepts of the proposed procedure for experimental determination of unsteady aerodynamic loads and its validity limits. We summarize the results of calculation of the dynamic stability limits for blade assemblies of compressor rotor wheels of a modern gas-turbine engine.     

Fatigue of VT20 titanium alloy with vacuum-plasma coatings at high temperatures

We study the influence of vacuum–plasma TiN, (TiAl)N, and (TiC)N coatings on the high-cycle fatigue of VT20 titanium alloy in the temperature range 350–640°C for a loading frequency of 10 kHz. It is shown that, in this temperature range, the fatigue limits of VT20 alloy with the indicated coatings 6 μm in thickness become 15–25% higher than for the material without coating. The possibility of replacement of steel blades with titanium blades with vacuum-plasma coatings is demonstrated. Translated from Problemy Prochnosti, No. 4, pp. 101–107, July–August, 2009.     

Causes of damages to fan blades of the generator of a steam turbine

It is shown that the fracture of blades of the fan of a TGV-200 generator is induced by corrosion fatigue intensified by residual hydrogen accumulated in steel in the process of electroplating of a cadmium coating on the surface of blades. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 3, pp. 109–112, May–June, 1997.     

Effect of attack angle on the nonstationary aerodynamic characteristics and flutter resistance of a grid of bent vibrating compressor blades

The angle of attack is studied by experiment for its effect on grid resistance to flutter for a plane compressor grid which includes four translationally vibrating blades. It is established that large critical angles of attack corresponding to stalled flow of blades increase sharply the probability of the occurrence of flutter both for individual blades and for the grid as a whole. It is shown that the reason for this phenomenon is a drop in aerodynamic damping of blades with single vibrations and a marked increase in their mutual aerodynamic effect.Translated from Problemy Prochnosti, No. 10, pp. 78–81, October, 1993.     

Cyclic strength of turbine blades made of cast nickel-based alloys

We study the cyclic strength and durability of service-exposed turbine blades made of IN-738, ZMI-3U, and éP539LM nickel alloys, some of them with a protective coating, upon a long operating time in gas turbine compressor sets. The blades of IN-738 alloy are found to have the highest cyclic strength. The cyclic strength of uncoated IN-738 blades is about 10% higher than that of coated blades. __________ Translated from Problemy Prochnosti, No. 2, pp. 5–14, March–April, 2007.     

Effect of the types of surface treatment and multilayer coating of turbine blade bodies on their fatigue strength

The technological characteristics of magnetoabrasive treatment of blade bodies used as a finishing operation in blade reconditioning and as a preliminary one in applying thin-layer coatings are studied. Fatigue testing of compressor blades with various types of surface treatment of the blade body and with a multilayer coating has been performed. A multilayer TiN coating is shown to exhibit good adhesion to the base metal, and blades with this coating have a higher fatigue strength and a lower scatter of durability values than after finishing polishing. Translated from Problemy Prochnosti, No. 5, pp. 109–116, September–October, 1999.     

Aerodynamic Levitation and Inductive Heating – A New Concept for Structural Investigations of Undercooled Melts

The combined application of containerless techniques with X-ray diffraction and absorption at synchrotron sources as well as neutron diffraction enables structural investigations of high-melting-point and/or corrosive liquids above the melting point and in the undercooled state. A variety of containerless techniques are available including electromagnetic and aerodynamic levitation. In the framework of a bilateral project, a new hybrid system combining aerodynamic levitation with inductive heating is being developed. Advantages and concept of the setup are discussed. Different Helmholtz coils and cylindrical coils were used to heat levitated, solid samples. Melting and stable levitation in the liquid state were achieved for aluminum. The general problem of deformation of liquid samples by electromagnetic fields is discussed. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Fatigue strength and life of compressor blades for marine gas turbine engines

An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have been justified. Investigations have been performed on the influence of manufacturing residual stresses and surface defects in the form of simulators of dents, corrosion pits, and nonmetallic inclusions on the fatigue strength of steels and a titanium alloy. The characteristics of the material crack growth resistance have been studied taking into account the effect of the medium (sea water), stress ratio in a cycle, and programmed mode of loading. The authors also consider fatigue strength of newly-manufactured blades and those in operation, as well as specific features of fatigue crack propagation in blades. They have substantiated a method for predicting the life of blades with cracks. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 28–40, January–February, 1999.     

轴流风机旋转叶片的气动噪声分析

针对某型轴流风机引起的气动噪声问题,建立该型轴流风机的三维模型,利用Lighthill声类比理论、FW-H声波波动方程和Fluent数值模拟,分析该轴流风机旋转叶片引起的气动噪声的噪声特性。数值模拟结果表明,旋转叶片上的静态压力主要集中在旋转方向前方的叶面上;而脉动压力则在叶片的两个面上均有分布,分布区域主要集中在叶片的外缘,这是由于叶片外缘脱落的旋涡引起的剧烈的气流震荡所导致。叶片上的气动噪声功率主要分布在叶片的外缘,其分布规律与脉动压力的分布规律有差异,表明旋转叶片的气动噪声并不完全由脉动压力产生。旋转叶片所诱发的气动噪声随着叶片转速和风机直径的增大而增大。     

变流器气动噪声分析与噪声控制研究

为控制某型号变流器噪声,文章对该变流器产品开展柜体内气动噪声仿真研究,并与试验结果对标,验证仿真方法可靠性,并协助进一步诊断噪声问题。仿真研究结果表明:机柜内部气动噪声源主要集中在风机附近区域,由风机叶片旋转引起的离散声源。风机噪声频谱在叶片通过频率及其他谐频出现明显峰值。文中对不同降噪方案进行仿真分析,对比了不同材料及不同厚度方案的降噪效果,并通过试验进行了验证。结果表明,使用吸声材料方案使出口总声压级降低 12.2 dB(A)。仿真分析法的降噪优化量与试验结果相近,该方法可应用于后续新产品的降噪设计。     

车用交流发电机气动噪声数值分析

以某型车用交流发电机（也称爪极发电机）为研究对象,采用计算流体力学技术对交流发电机的空气动力学特征进行了三维非定常数值模拟,应用滑移网格技术和大涡模拟方法对交流发电机进行气动噪声特性研究。得到大涡模拟在交流发电机噪声数值预测方面其主要阶次和对应的幅值与试验对比有很好的一致性;前后扇叶为该型交流发电机的气动噪声声源;第6、8、10、12和18等阶次为该型交流发电机的主要气动噪声成分。在数值模拟基础上,以低噪声、高流量为优化目标,对交流发电机前端盖径向栅格分布角度进行气动噪声优化设计及降噪研究。得到前端盖径向栅格倾斜40°分布角度时交流发电机远场气动噪声最低、质量流量最大。文中所得研究成果可为车用交流发电机的气动性能和高转速下噪声的改进提供一种切实可行的参考依据。     

Creep-life prediction of service-exposed turbine blades

We study the possibility of prediction of the service life of gas-turbine blades made of nickel alloys according to the results of accelerated testing of specimens cut out from these blades. The predictions are carried out with the help of two methods: by using the Larson-Miller parameter and according to Robinson’s rule. It is shown that the predictions performed by using the Larson-Miller parameter on the basis of extrapolation of the data of accelerated tests are possible but give underestimated results for the durations of service life greater than 80,000 h, which is explained by the changes in the microstructure of the material in the course of long-term operation of the blades. Published in Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 49–53, July–August, 2006.