Stall prediction of in-flight compressor due to flamming of refueling leakage near inlet

 The propagation of strong distortion at inlet of an axial compressor is investigated by applying the critical distortion line and the integral method. The practical applications, such as the inlet conditions of flaming of leakage fuel during mid-air refueling process, are implemented to show the details of the numerical methodology used in analysis of the axial flow compressor behavior and the propagation of inlet distortion. 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 simulated results present a useful physical insight to the significant effects of inlet parameters on the distortion extension, velocity, and compressor characteristics. The distortion level, incidence angle and the size of distortion area at compressor inlet, and the rotor blade speed are found being the major parameters affecting the mass flow rate of engine. Received: 20 October 2002 / Accepted: 28 January 2003 The authors would like to thank HQ RSAF of Air Logistic Department, Singapore for permission to publish this work, their financial support and encouragement.     

板带式速冻机内部通道流场的数值模拟

用PHOENICS软件对某型板带式速冻机载货板带运动时的内部通道流场进行了数值计算.分析了板带运动、空气进口速度、流动通道高度、空气入射角对内部流场的影响.研究表明:正常工况下板带运动对流动通道空气速度分布没有影响;空气进口速度和通道高度的选取应该综合考虑空气流速大小,流速均匀性,流动阻力损失三方面因素;最佳空气入射角应该为0度.     

Endwall boundary layer separation in a single-stage axial-flow low-speed compressor and a high-stagger compressor cascade

The paper describes an investigation of the overtip endwall flow in a single-stage axial-flow low-speed compressor (absolute flow) and in a corresponding compressor cascade (simulated relative flow) with a tip clearance on one side. The clearance to chord ratio is 3% in both cases. Oil flow pictures of the rotor casingwall and cascade endwall are used to visualize and analyse the boundary layers on the walls at various flow rates and corresponding inlet angles, respectively. The results enable the different sources of endwall blockage to be identified and changes with flow rate or inlet angle to be determined.     

Endwall boundary layer separation in a single-stage axial-flow low-speed compressor and a high-stagger compressor cascade

The paper describes an investigation of the overtip endwall flow in a single-stage axial-flow low-speed compressor (absolute flow) and in a corresponding compressor cascade (simulated relative flow) with a tip clearance on one side. The clearance to chord ratio is 3% in both cases. Oil flow pictures of the rotor casingwall and cascade endwall are used to visualize and analyse the boundary layers on the walls at various flow rates and corresponding inlet angles, respectively. The results enable the different sources of endwall blockage to be identified and changes with flow rate or inlet angle to be determined.     

The effects of element shape on the critical time step in explicit time integrators for elasto‐dynamics

In this paper, the effects of element shape on the critical time step are investigated. The common rule‐of‐thumb, used in practice, is that the critical time step is set by the shortest distance within an element divided by the dilatational (compressive) wave speed, with a modest safety factor. For regularly shaped elements, many analytical solutions for the critical time step are available, but this paper focusses on distorted element shapes. The main purpose is to verify whether element distortion adversely affects the critical time step or not. Two types of element distortion will be considered, namely aspect ratio distortion and angular distortion, and two particular elements will be studied: four‐noded bilinear quadrilaterals and three‐noded linear triangles. The maximum eigenfrequencies of the distorted elements are determined and compared to those of the corresponding undistorted elements. The critical time steps obtained from single element calculations are also compared to those from calculations based on finite element patches with multiple elements. Copyright © 2014 John Wiley & Sons, Ltd.     

An analytical approach for simple shear extrusion process with a linear die profile

In the present work, for the first time, an analytical approach based on upper-bound theorem is proposed to analyze the simple shear extrusion process. In this regard new die parameter named maximum inclination angle is introduced. By this model, the power dissipated on all frictional and velocity discontinuity surfaces is determined and the total power is optimized for two types of die, fixed and movable inlet channel die. To check the validation of the upper-bound model, the process is simulated by the commercial finite element code, Deform-3D. To compare the theoretical results with experiments, a fixed inlet channel die and two dies with movable inlet channel are used to determine the processing force for different cross sections. The developed model predicts that the relative extrusion pressure increases with increasing the constant friction factor; also, for a given value of the constant friction factor and the maximum distortion angle, there is an optimized maximum inclination angle which minimizes the power. Comparing the fixed inlet channel die with the movable inlet channel one, it is seen that the optimized maximum inclination angle is higher in the FIC die.     

制冷系统变工况性能数值模拟

采用分布参数法建立制冷系统数学模型,在建立冷凝器和蒸发器两相区模型时采用分相流模型,并考虑流型变化对制冷剂流动换热过程的影响。利用所建模型,分析电子膨胀阀开度、压缩机转速、冷凝器风速等参数变化对系统性能的影响,为控制规律的研究提供依据。     

GE9FA燃气轮机进气加热系统的控制

当9FA燃气轮机压气机进口温度低时,为防止压气机进口结冰和超过运行极限,9FA燃气轮机的运行范围将受到限制。为了降低排放和防止压气机进口结冰,根据压气机进口可转导叶(IGV)来控制进气加热。压气机进气加热是将部分压气机的排气循环到压气机进口。该系统有三个作用:1)防止压气机进口结冰;2)通过降低IGV角度来满足低负荷时的排放要求,降低压气机压比;3)保证压气机有足够的安全裕度。进气加热系统保证了压气机的全范围运行。     

发动机室内试车台流场品质研究

流场品质对航空发动机室内试车台上性能试验结果有重要影响,高品质流场是室内试车台进行气动附加阻力准确修正的基础。本文对比介绍了国内外室内试车台气动流场参数要求差异,分析了室内试车台进排气结构等因素对流场品质的影响,提出了以试车间气流速度均匀性、引射比、进气道总压均匀性为核心参数的流场品质评价参数体系,并针对未来国内室内试车台在提高流场品质方面需开展的工作提出了建议。     

Flow imaging with pulsed Doppler ultrasound and flow phantoms

The use of a multigate profiling system with steady laminar flow in plastic tubes revealed spectral artifacts not previously described. In particular, a double or split profile was often observed. In this paper, these artifacts are related to the dual mode ultrasound propagation in the plastic tube. The propagation speeds and, therefore, refraction angles and propagation paths are different for the longitudinal and the shear wave. The power transmission can be extraordinarily sensitive to small variations in the angle of incidence, and this may combine with the existence of a range of angles of incidence within any focused ultrasound beam to produce spectral distortions. The plastic tube is thus shown equivalent to a selective filter, which diminishes some frequency components in the Doppler spectrum relative to others. The spectral artifacts are explained in terms of the relative power transmitted by each mode, and the degree of beam defocusing experienced by each. Spectral distortions persist even when the beam-to-flow orientation is well away from the critical angle. The results of this study show that it is feasible to understand the acoustic transmission behavior of a flow phantom, based on a knowledge of the material properties, and to demonstrate the usefulness of doing so.     

Flow visualization applied to a small refrigeration compressor

This paper describes a flow visualization technique that was used to evaluate qualitatively the gas flow pattern inside a small, hermetically sealed, reciprocating refrigeration compressor. The applicable compressor designs are those in which the suction gas from the evaporator is dumped into the compressor shell, and is then drawn through a muffler into the suction plenum of the compressor. The physical separation of the muffler inlet from the suction gas inlet serves to reduce compressor noise and also provides an easy and convenient means of separating any liquid (compressor oil or liquid refrigerant) from the refrigerant gas. For the flow visualization studies the compressor housing was replaced by a clear plastic shell. Atmospheric air seeded with white smoke was the working fluid. The suction inlet and muffler were parts from a commercial compressor. The flow pulsations were modelled by connecting the muffler outlet to the input plenum of an auxiliary compressor. The flow patterns near the muffler inlet were recorded with a video camera. The mixing of the inlet gas with the gas circulating inside the muffler was studied. The effect of alignment and offset of the muffler inlet relative to the suction inlet, the effect of muffler size, and the effect of a shroud around the muffler were studied. The results were used to guide a companion study of detailed temperature and pressure measurements inside a working compressor.     

A parametric study of dispersed laminar gas-particle flows through vertical and horizontal channels

Particle diameter, particle phase material density and inlet particle volume fraction are three important parameters governing the flow physics of dispersed gas-particle flows. In this work, an inhouse numerical solver is developed to investigate the effects of particle diameter (Stokes number), particle phase material density, inlet particle volume fraction and inlet phase velocities in the flow characteristics of gas-particle flows through vertical and horizontal channels and also in open domains. It is found that, for a constant inlet particle volume fraction, lower diameter particles attain a higher steady state velocity at any section inside the channel than the higher diameter particles; while the corresponding steady state gas velocity at any section increases with increase in particle diameter. On the other hand, for a constant particle diameter, the steady state gas phase velocity at any section decreases with increase in inlet particle volume fraction. Significant changes in both gas and particle velocity and volume fraction profiles have also been observed with inlet slip, i.e., when the velocities of both the phases at inlet are distinct as opposed to being equal, keeping all other flow and physical parameters invariant.     

The influence of inlet velocity profile on three-dimensional three-generation bifurcating flows

 The influence of inlet velocity profile on the three-dimensional three-generation bifurcating flow has been numerically studied using a CFD code based on finite volume method. The bifurcating airways simulated the branches of human lung. The axial length and cross-sectional diameter of the three-generation airway are taken from the anatomic data of the 5th–7th generation airway of an averaged height man. The curvature and bifurcating angle of each junction are taken as 2.265 diameter of the next generation and 70^∘, respectively, from physiological consideration. Computations are carried out for eight Reynolds numbers ranging from 200 to 1600, each under uniform and parabolic inlet velocity profiles, to consider the relations between the entry flow patterns and the overall flow characteristics including mainstream flow pattern, secondary flow vortices, asymmetrical flow partition and pressure drop. The mass flow ratio between the medial and lateral branch, and the total pressure drop are closely related to the entry flow patterns for larger Reynolds numbers. Received: 1 October 2001 / Accepted: 12 July 2002 Support given by the Research Grants Council of the Government of the HKSAR under Grant No. PolyU 5166/01E and by the Hong Kong Polytechnic University under Central Research Grant No. A-PD75 is gratefully acknowledged.     

Development and evaluation of virtual refrigerant mass flow sensors for fault detection and diagnostics

Refrigerant mass flow rate is an important measurement for monitoring equipment performance and enabling fault detection and diagnostics. This paper presents and evaluates three different virtual refrigerant mass flow (VRMF) sensors that use mathematical models to estimate flow rate using low cost measurements. The first model uses a compressor map that relates refrigerant flow rate to measurements of condensing and evaporating saturation temperature, and to compressor inlet temperature measurements. The second model uses an energy-balance method on the compressor that uses the compressor power consumption. The third model is developed using an empirical correlation for an electronic expansion valve (EEV) based on an orifice equation. The three VRMFs are shown to work well in estimating refrigerant mass flow rate for various systems under fault-free conditions with less than 5% RMS error. The combination of the three VRMFs can be utilized to detect and diagnose when the compressor and/or expansion device is not providing the expected flow.     

Influence of inlet angle on flow pattern and performance of gas-liquid cylindrical cyclone separator

Gas-liquid cylindrical cyclone (GLCC) separator is widely used in the petroleum industry with potential field applications. Its performance is strongly influenced by the inlet configuration. The 27° optimal inclined inlet angle has been experimentally observed for GLCC with the same diameter of body and inlet. For other GLCCs, the effect of inlet angle on flow pattern and their performances have not been investigated. The main target of the current study is to deeply understand the changes of flow pattern with respect to different inclined angles and flow conditions. Twelve GLCCs with different inclined angles were numerically investigated by using the Reynold stress turbulence model to predict the flow pattern with GLCC. The distribution of radial, axial, and tangential velocity profiles and their maximum magnitudes with respect to the change of inlet angle were carefully considered in this study.     

Reflection of plane waves at the free surface of a fibre-reinforced elastic half-space

The propagation of plane waves in fibre-reinforced, anisotropic, elastic media is discussed. The expressions for the phase velocity of quasi-P (qP) and quasi-SV (qSV) waves propagating in a plane containing the reinforcement direction are obtained as functions of the angle between the propagation and reinforcement directions. Closed form expressions for the amplitude ratios for qP and qSV waves reflected at the free surface of a fibre-reinforced, anisotropic, homogeneous, elastic half-space are obtained. These expressions are used to study the variation of amplitude ratios with angle of incidence. It is found that reinforcement has a significant effect on the amplitude ratios and critical angle     

摄像机径向畸变校正和内参估计的单图标定方法

提出了一种对摄像机的径向畸变进行校正和内参数估计的单图标定方法.拍摄一幅平面标定模板图像,提出若干条直线,拟合在单参数除法畸变模型下的圆弧参数,从而估计出径向畸变.对径向畸变进行校正后,利用标定模板点与经过校正后的图像点之间的对应关系,估计出单应性矩阵.在假定摄像机主点与畸变中心重合的条件下,线性地计算出摄像机焦距初值.以上述线性方法得到的结果为初值,进行非线性优化,最终得到准确的摄像机参数.超广角鱼眼相机和普通数码相机的实验结果表明,本文提出的算法实现简单、适用性广,结果准确,具有较强的实用性.     

基于CFD和试验的商用车高位引气管预滤性能的 分析与优化

为延长恶劣工况下某商用车进气系统空气滤清器滤芯的使用寿命,避免频繁更换滤芯,提出了增加旋流扇的高位引气管方案,并通过优化旋流扇夹角来提高进气系统预滤灰尘和液雾的效率,达到降低成本的目的。首先,采用计算流体力学（computational fluid dynamics,CFD）方法,对进气过程中高位引气管的内部流场进行数值模拟,分析了3款高位引气管的速度流线图和速度梯度云图,得到了高位引气管预滤灰尘和液雾的机理,并基于高位引气管速度流场的变化规律,提出了旋流扇夹角优化方向;其次,利用台架试验对优化后的高位引气管进行灰尘和液雾的预滤试验,并计算出灰尘和液雾的预滤效率;最后,对比不同高位引气管预滤灰尘和液雾的效率,根据两预滤效率的变化趋势,选择旋流扇最优夹角为75°。仿真和试验结果表明：旋流扇夹角对进气系统工作过程中高位引气管的流场及预滤效率有重要影响,优化旋流扇夹角有助于提高进气系统的预滤性能,从而减少进入空气滤清器的灰尘和液雾,达到延长空气滤清器滤芯寿命的目的。     

Wavelet-based distortion measure for binary images

Abstract

This paper proposes an objective distortion measure for binary images. Whereas most previously proposed measures decide the distortion weight of a distorted pixel based on the relationship with the neighbouring pixels in the spatial domain, we observe the characteristics of distorted pixels in multi-spectral spatial-frequency bands. Similarities between the binary wavelet transform and the human visual system are utilised to obtain the distortion weight. When we decide the distortion weight of a distorted pixel, we consider flatness, edge orientation and texture complexity of the distorted pixel at each level of binary wavelet decomposition. Experimental results on various sample images show that the proposed measure is more adequate to human than previously proposed measures.     

基于Aspen Plus的自复叠热泵模拟

自复叠热泵的变工况运行对其性能影响很大。应用Aspen Plus软件,对冷凝器入口水温从40～55℃的4个工况下的自复叠热泵进行了流程模拟,并对流程中各点参数变化进行了分析,对节流阀的流态进行了计算分析。结果表明,自复叠热泵在两个节流阀开度不变时,随着冷凝器入口水温的升高,压缩机耗功增加,主流与支流流量增大,蒸发压力升高,压缩机入口比容减小,循环的质量流量增大;两个节流阀均未达到雍塞流。