轴流压气机旋转失速和喘振的非线性反馈控制

旋转失速和喘振是轴流压气机中的两种主要的不稳定工作形式,限制了压气机稳定工作范围。本文中提出了一种新的对旋转失速和喘振的非线性反馈控制策略,即把压升作为反馈信号,来补偿节流阀系数值。研究结果表明,这种控制策略很简单,但是能够消除失速时伴随的迟回效应;也能够增加压气机的喘振裕度。     

Failure investigation of blade and disk in first stage compressor

A matched blade tenon and disk mortise of the first stage compressor in an aeroengine fractured simultaneously. Apparently, both had fatigue features on the fracture surfaces. Macro observations showed the cracking sites were roughly at the central region of the matched tenon and mortise. Contact surfaces examination revealed there were important marks, showing abnormal contact of the tenon and mortise in service. Material qualities were inspected and the stresses in the tenon and in the mortise were calculated under normal conditions. These demonstrate that the failures were not due to the insufficiency of failure resistance but the deviation from expected conditions. Conclusively, the bad contact of the tenon and the mortise is responsible for the failures. Field non-destructive inspection was performed on other aeroengines of the same type, and some cracks, which were very similar to those in the fractured tenon and mortise, were found. Further investigation revealed that the design shortcoming resulted in over-compensation of centrifugal bend moment and bad contact condition.     

Study on the propagation of inlet flow distortion in axial compressor using an integral method

 An integral method is investigated and developed in the current work. The effects of the parameters of inlet distortions on the trend of downstream flow feature in compressor are simulated. Other than the drag-to-lift ratio of the blade and the inlet incidence angle, it is found that the distorted inlet velocity is another essential parameter to control the distortion in propagation. Based on this study, a novel critical distortion line and corresponding critical distortion factor are proposed to express the effect of the two essential inlet parameters on the propagation of distortion, namely, the inlet incidence angle and the distorted inlet velocity. From the viewpoint of compressor efficiency, the propagation of inlet flow distortion is further described by a compressor critical performance and its critical characteristic. The results present a useful physical insight to an axial flow compressor behavior and asymptotic behavior of the propagation of inlet distortion, and confirm the active role of compressor in determining the velocity distribution when compressor responds to an inlet flow distortion. Received: 20 December 2001 / Accepted: 21 August 2002 The authors would like to thank HQ RSAF for permission to publish this work, their financial support and encouragement. The first author wants to acknowledge Prof. Frank Marble of California Institute of Technology, for bringing the problem to the author's attention and for his helpful discussion.     

部分失速工况下轴流压气机转子受力特性的研究

首次将轴流压气机的受力特性与工况相结合,分析压气机转子的速度变化和受力特性。首先从理论角度阐述了轴流压气机的失速原理及过程,然后对压气机在正常运行工况和部分失速工况下的受力表达式进行理论推导,通过仿真得出轴流压气机在部分失速工况下的受力特性,最后将仿真结果与理论推导部分相对比。论文通过仿真验证了理论分析的可行性,并得出了失速工况下轴流压气机的速度变化与受力特性,为后续转子的振动分析以及转子的结构优化设计提供有益参考。     

Experimental study on influencing factors of axial clearance for scroll compressor

An experimental system of non-contact measurement has been established for a scroll compressor to analyze the influencing factors of axial clearance. Experimental method and installation for eddy current displacement sensors have been introduced in detail based on technical analysis. The output voltage input into a computer through analog oscilloscope is recorded by oscilloscope software. The axial clearance is calculated according to the relationship between the output voltage and displacement. The axial clearance is discussed under the influence of different rotary speed, temperature and position. The results show that the experimental schemes are reasonable to realize the detection of the dynamic axial clearance. Temperature and rotary speed are inversely proportional to the axial clearance. The effect of rotary speed on the axial clearance is more noticeable than that of the temperature. The axial clearance along the spread angle of scroll profiles is obviously fluctuating under the action of overturning moment.     

Effects of casing treatment on behavior of tip leakage flow in an isolated axial compressor rotor blade row

This article deals with enhancement in aerodynamic performance of an isolated axial compressor rotor blade row while applying treated casing. Three dimensional unsteady flow is assumed and a flow solver, utilizing Large Eddy Simulation (LES), is undertaken for the numerical calculations. Unsteady tip leakage flow and its propagation trajectory are simulated in detail for both smooth and treated casings. Oscillatory nature of tip leakage flow is depicted and its frequency is calculated by the calculation of pressure distribution along the rotor blade tip, for smooth and treated casings. For the smooth casing and in comparison with experimental data, results showed that in contrast with the Reynolds Averaged Navier–Stokes method, the LES realizes dependency of frequency characteristics of the tip leakage flow on the blade tip clearance size, and also can recognize different frequency characteristics of the tip leakage flow along the blade chord. Results also demonstrated that performing casing treatment causes the amplitude of unsteadiness of tip leakage flow to reduce and its frequency to get closer to the blade passing frequency. This in turn, causes flow blockages and losses in total pressure to reduce.     

Experimental investigation of axial dispersion in a horizontal rotating cylinder

This work reports experimental measurements of the dispersion of particles during rotation in a horizontal cylinder. The axial dispersion of a pulse of approximately monodisperse black glass ballotini into a bed of clear glass ballotini of the same size is analysed. This is done using a sectioning technique, where the concentration is determined throughout the cylinder for a given rotation time and speed. The concentration profile is fitted to an appropriate solution of Fick’s second law to determine the dispersion coefficient. The dispersion coefficient is compared for various drum rotation rates and glass ballotini sizes. The cylinder was filled to 35 % by volume and rotated at a range of speeds between 5 and 20 rpm. The particle sizes vary from 1.14 to 3.15 mm. The dispersion coefficient was found to be dependent on both particle size and rotation speed. As the rotation speed, \(\omega \), was increased the dispersion coefficient increased proportionally to \(\omega ^{0.8}\). As the particle diameter, \(d_p\), was increased the dispersion coefficient increased proportionally to \(d_p^{1.84}\). These results are compared with previous experimental and simulation data, in particular the simulations of Third et al. (Powder Technol 203:510, 2010). Strong agreement was found between the simulations of Third et al. and the experimental results.

     

Experimental study of the axial force on the rotors in a twin-screw refrigeration compressor

The high operating pressure of a twin-screw compressor employed in high temperature heat pump or NH₃/CO₂ cascade refrigeration systems often leads to extremely large axial force on the compressor rotors. Accurate calculation of this axial force is very important in selection of bearing and design of balancing pistons. In this paper, an experimental study of the axial force on the twin-screw compressor rotors was conducted. The variations of the axial force under different operating conditions were investigated. Furthermore, the axial force was also calculated by employing the mean pressure model and sector pressure model, and was compared with that of the experimental results. It was concluded that the sector pressure model is more accurate in predicting the axial force on the rotors in comparison with that of the mean pressure model. However, the mean pressure model was more accurate under operating conditions with large built-in volume ratio. Moreover, the axial force on the rotor end face was found to have larger influence than that on the rotor helical surface.     

Experimental investigation of a.c. losses in cabled superconductors

A.c. losses in multifilamentary composite superconducting strands and cables have been measured in adiabatic conditions for transverse field sweep rates up to 50 T s⁻¹. Measurements were performed on NbTi and Nb₃Sn conductors of several configurations and surface preparations: single strands, soldered strands and cables of varying degrees of compaction composed of bare strands, strands with CuNi barriers and strands with chrome plating. The experimental data agree well with existing loss models. Loss data are characterized in terms of effective coupling current time constants. It has been determined that chrome plating on strands can reduce the coupling loss in highly compacted cables to as little as 20% of the coupling loss in similar cables composed of bare strands. In loosely compacted cables (down to ≈ 50% void) the strand-to-strand coupling loss was less than the filament coupling loss. As compaction is increased below 50% void the strand coupling quickly increases and becomes the dominant loss mechanism. The data suggest that the total cable loss grows as ≈ 1/(void)³ below void fractions of 40%. This observed cable loss dependence on void fraction does not agree well with a previously proposed model.     

Experimental investigation on convective heat transfer mechanism in a scroll compressor

This paper describes an experimental study on the convective heat transfer inside the scroll compressor. An experimental refrigeration system is composed with extensive instrumentations in the compressor that is operated at variable speeds. The 13 thermocouples installed inside the compressor monitor the temperatures of the scroll wrap during compression process of refrigerant. The temperature and the pressure of refrigerant at suction, and the pressure at discharge ports are measured, and applied to the numerical simulation as the operating condition parameters. The temperature measured at the discharge port is used to verify the simulation result with relevant heat transfer coefficient. This paper describes the effect of motion of the orbiting scroll on the convective heat transfer in the scroll wraps. Separate experiments are performed to investigate the heat transfer in such a peculiar physical condition. With this experimental result, the effect of the oscillation of the wall on the heat transfer is quantitatively analyzed and applied to the simulation of compression process in scroll compressor. The whole consecutive compression processes in the scroll compressor is simulated in detail by solving equations of mass and energy balance for the refrigerant. The modified heat transfer coefficient correlation considering the effect of motion of the orbiting scroll predicts the discharge temperature better than other typical heat transfer coefficients.     

Experimental investigation of supersonic flow about an obstacle with power delivery into the undisturbed flow

A technique and results of experimental investigation of supersonic flow about bodies with optical breakdown in the windstream are presented. Flow parameter evolution when pulsed power is delivered locally is tracked. Experimental and calculated flow patterns are compared.A.F. Mozhaiskii Military Space-Engineering Institute, St. Petersburg. Translated from InzhenernoFizicheskii Zhurnal, Vol. 66, No. 5, pp. 515–520, May, 1994.     

Experimental investigation of exergy losses of a PEM fuel cell system

Objective of this work is the experimental determination of exergy losses of the PEM fuel cell system Nexa from Ballard for different steady-state operating points. After selection of appropriate system boundaries experimental data are substituted into balance equations of the first and second law of thermodynamics. The results are exergy losses due to heat transfer from the stack to the cooling air, due to dissipation of electric power by electronics and due to irreversible electrochemical processes of the stack. These different exergy losses are compared to identify the sub-process with the largest exergy loss and therefore the largest optimization potential.     

Experimental testing of an oil-flooded hermetic scroll compressor

In this work, a residential air conditioning compressor designed for vapor injection has been modified in order to inject large quantities of oil into the working chamber in order to approach an isothermal compression process. The compressor was tested with oil injection mass flow fractions of up to 45%. At an evaporating temperature of ?10 °C and condensing temperature of 30 °C, the overall isentropic efficiency was up to 70% at the highest oil injection rate. Overall, over the testing envelope investigated, there are no significantly negative effects experienced for the compressor and the compressor isentropic efficiency and refrigerant mass flow rate improve monotonically as the oil injection rate is increased.     

Experimental investigation of the three-dimensional structure of detached flow in an axisymmetric annular diffusor

It is shown experimentally that stream detachment in an annular diffusor has a stabilized, three-dimensional, periodic structure.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 2, pp. 321–328, August, 1986.     

Experimental investigation of acoustic substrate losses in 1850-MHz thin film BAW resonators

After optimizing for electromechanical coupling coefficient K², the main performance improvement in the thin film bulk acoustic wave resonators and filters can be achieved by improving the Q value, i.e., minimizing the losses. In Braggreflector- based solidly mounted resonator technology, a significant improvement of Q has been achieved by optimizing the reflector not only for longitudinal wave, the intended operation mode, but also for shear waves. We have investigated the remaining acoustic radiation losses to the substrate in so-optimized 1850-MHz AlN resonators by removing the substrate underneath the resonators and comparing the devices with and without substrate by electrical characterization before and after the substrate removal. Several methods to extract Q-values of the resonators are compared. Changes caused by substrate removal are observed in resonator behavior, but no significant improvement in Q-values can be confirmed. Loss mechanisms other than substrate leakage are concluded to dominate the resonator Q-value. Difficulties of detecting small changes in the Q-values of the resonators are also discussed.     

Experimental investigation of a direct driven radial compressor for domestic heat pumps

The presence of oil in domestic heat pumps is an obstacle toward higher efficiency, particularly for enhanced surface evaporators and for advanced concepts based on two-stage cycles. Very compact direct driven radial compressors supported on oil-free bearings represent a promising alternative. This paper presents the derivation of the specifications, the choice for an appropriate refrigerant fluid and the design of a proof of concept prototype with the various tradeoffs between the impeller characteristics to follow the seasonal heat demand, the bearing and rotordynamics for a stable operation. Heat pump simulation results, the design of the impeller as well as the layout of the experimental facility and first experimental results are presented. An impeller with a tip diameter of 20 mm has been tested at rotational speeds of up to 210 krpm reaching pressure ratios in excess of 3.3 and efficiencies above 78%. The refrigerant chosen for this first experimental approach is HFC 134a.     

螺杆式空气源热泵机组压缩机油位试验研究

分析压缩机吸气回液、外置油分离器油分离效率对螺杆式空气源热泵机组压缩机油位的影响,提出改进翅片换热器分液、优化气液分离器结构、改善油分离器分离方式等改进措施,并对螺杆式空气源冷（热）水机组进行试验。结果表明,所提改进措施不仅能够提高压缩机运行过程中的油位,而且能够提高机组运行稳定性。     

Simulation of fatigue failure in composite axial compressor blades

Centrifugal forces are generated by a spinning impeller, of magnitudes that create large stresses. Aerodynamic forces are also imparted on an impeller blade, which varies with time and position. These two forces play different roles during compressor events. Damage accumulated from these events results in the fatigue failure of impeller material and structure. Therefore, it is important to design an impeller against dynamic and fatigue failure. The finite element method has been used in the study of impeller fracture mechanics and is regarded as an important tool in the design and analysis of material and structures.     

Experimental investigation of an ejector

The purpose of this work is to provide technical data for the proper design of gas ejectors, in particular for applications with helium.