轴向间距对压气机失速特性的影响

采取在静子叶片表面埋入微型压力传感器的方法,对叶尖、叶中和叶根三个截面上的动态压力进行测量,实验研究了六个轴向间距下压气机的旋转失速特性。实验结果表明:轴向间距对压气机失速点的流量系数影响很大,转静子轴向间距减少,压气机失速推迟;压气机刚进入旋转失速的模态与轴向间距有关,轴向间距较大时,压气机首先进入多团全叶高旋转失速,当轴向间距为21％CR时,压气机直接进入单团全叶高旋转失速;轴向间距不同,近失速点的压力扰动也存在差别。     

进气畸变对压气机稳定性的影响

在低速大尺寸单级压气机实验器上,实验研究了动态进气畸变对压气机稳定边界的影响。并采取在静子叶片表面埋入微型压力传感器的方法,分析了压气机流场的动态压力特性。实验结果表明,动态总压畸变的旋转频率和旋转方向对压气机稳定性有很大的影响,当畸变相对转速n在0~+0．5之间时,压气机失速推迟;分析动态压力的频谱特性后知道,在压气机失速前一般存在与失速相关的压力扰动,动态总压畸变影响这种压力扰动,从而影响压气机的不稳定流动状态。     

单级跨声速压气机旋转失速模拟方法

为了研究多排跨声轴流压气机旋转失速先兆的表现形式与失速演化规律,基于自主研发的CFD软件ASPAC,通过发展动态重叠网格技术,流量出口边界条件以及节流阀边界条件,对单级跨声速压气机NASA Stage 35由近失速状态到完全失速状态的过程进行了模拟.结果表明,发展的数值模拟方法能准确地模拟多排压气机的旋转失速发展过程;均匀进气条件下,随着NASA Stage 35向失速状态逼近,某些动叶压力面前缘出现了叶顶间隙流溢流现象,促使压气机进入旋转失速状态;在失速先兆阶段,周向非均匀流动开始出现并沿压气机周向传播;当完全失速时,失速团充分发展并连续地沿周向旋转,结构几乎不随时间变化.      

轴流压气机旋转失速先兆过程中-的频率阶跃现象

本文采用小波分析数据处理方法,分别对高速和低速单级轴流压气机旋转失速先兆的发生和发展过程进行了分析,结果发现两台压气机的旋转失速先兆都是由脉冲开始,随之出现频率逐渐阶跃的低频波,当阶跃频率到达失速频率时压气机进入失速。在高速实验台上发现这一现象的出现沿叶片通道方向由后向前延迟。     

旋转进口畸变与轴流压气机旋转失速相关联的模型与实验探索

本文自行设计了轴流压气机旋转进口畸变发生装置.基于M-G模型,建立了轴流压气机旋转畸变模型.采用数值模拟和实验测量相结合的方法研究了轴流压气机在发生旋转进口畸变情况下的失速过程.试图通过分析畸变扰动与旋转失速之间关联性来探索压气机失稳的触发机理.研究结果表明:在旋转畸变条件下,压气机旋转失速总是始发于畸变扰动位置.     

基于小波变换的离心压气机旋转失速先兆时频分析

本文采用连续小波变换的方法,对跨音离心压气机机壳壁面动态压力及叶片应变信号进行了时频分析。结果表明,在失速前的先兆阶段存在着两种特征截然不同的先兆成分。即连续增强成分和间断扰动成分。间断扰动成分和间断失速段的失速团具有相近的特性．压力信号中间断失速段的失速团频率比在连续失速段的失速团频率高,而叶片应力信号中则相反,并计算得出连续失速段的失速团比间断失速段的失速团数目少。在间断失速段,压力信号的频率阶跃以及叶片应变信号的频率衰减现象,对应于扰动能量聚集而使失速团数目减少的过程。     

叶尖喷气影响失速起始型式的数值研究

以某叶尖失速型的轴流压气机转子为研究对象,开展了无叶尖喷气以及喷气量为1%边界流量情况的全通道非定常数值模拟。数值探针监测结果表明:不喷气时出现了与实验测量结果一致的突尖型失速,而喷气情况下出现的是模态型失速。对比叶尖喷气下不同工况点的瞬态流场发现:在喷气流影响的径向范围内,喷嘴右侧通道中间隙泄漏流和吸力面尾缘分离耦合作用形成的流动阻塞,随着流量的减小逆转子转动方向沿周向扩展;而喷气流影响的径向范围外,喷嘴左侧通道中吸力面尾缘分离形成的流动阻塞顺转子转动方向沿周向扩展。这种流动阻塞格局的发展演化是喷气情况下出现模态扰动的原因。     

周向进口畸变对压气机失速过程的影响

本文对一台带有不同周向进口畸变装置的三级、低速、轴流压气机进行实验研究。研究结果发现周向进口畸变对压气机失速过程的影响包括了最初始的大时间尺度扰动产生的位置与条件;大时间尺度扰动失速先兆向脉冲型失速先兆的转化,以及大时间尺度扰动失速先兆尺度随转子转动方向的逐渐减小。说明局部扰动和系统特性之间存在一定的相互关系。     

小波方法分析小流量喷气影响两级低速轴流压气机失速特性的动态效果研究

本文用连续小波变换和二维图像处理方法对三个不同角度的喷气试验数据进行了分析．通过对比分析，连续小波变换发现失速前转速频率成分的能量在两级动叶前的信号中出现波动现象，而这种波动的强度与喷射角有关；二维小波图像分析发现，压力场中相对于叶片通道而言的大尺度奇异性均在失速前呈波动性增强，这种波动以接近转子转速沿压气机周向旋转，喷射角度对失速前的奇异性及其波动程度有明显影响．一维小波方法和二维方法的结果相互对应，但二维方法更加具有优势．     

离心压气机突尖失速预测与模态识别方法

本文以带有蜗壳的离心压气机为研究对象,首先采用压缩动态模态分解方法对叶轮失速扰动结构进行提取和分析;其次,基于线性稳定性理论,建立叶轮入口z-θ圆柱面的二维稳定性分析方法,对失速诱发的流动失稳扰动传播进行研究.结果表明,由叶片前缘溢流引起的失速扰动可以分解为四种形式:基本流场扰动、叶频和转频引起的扰动、压气机在失速先兆...     

Scanning moiré and spatial-offset phase-stepping for surface inspection of structures

In order to develop a high-speed and accurate surface inspection system of structures such as tunnels, a new surface profile measurement method using linear array sensors is studied. The sinusoidal grating is projected on a structure surface. Then, the deformed grating is scanned by linear array sensors that move together with the grating projector. The phase of the grating is analyzed by a spatial offset phase-stepping method to perform accurate measurement. The surface profile measurements of the wall with bricks and the concrete surface of a structure are demonstrated using the proposed method. The change of geometry or fabric of structures and the defects on structure surfaces can be detected by the proposed method. It is expected that the surface profile inspection system of tunnels measuring from a running train can be constructed based on the proposed method.     

On the two-point cross-correlation function of anisotropic, spatially homogeneous ambient noise in the ocean and its relationship to the Green's function

It is well established that the free-space Green's function can be recovered from the two-point cross-correlation function of a random noise field if the noise is white and isotropic. Ambient noise in the ocean rarely satisfies either of these conditions. However, a non-uniform spectrum could be pre-whitened by the application of a suitable filter but anisotropy cannot be so readily eliminated. To investigate the effects of vertical anisotropy, three azimuthally uniform, spatially homogeneous noise fields are analyzed, two of which are idealized, while the third is representative of ambient noise in the deep ocean. In each case, the coherence function, the cross-correlation function, and the derivative of the latter with respect to the correlation delay, are derived for vertical and horizontal alignments of the sensor pair. With vertical sensors, any step-function discontinuity in the directional density function is mapped into a delta function at an appropriate time delay in the derivative (with respect to time delay) of the cross-correlation function. No such mapping occurs with horizontal sensors. In this case, only horizontally traveling noise can generate delta functions in the derivative of the cross-correlation function, and these always appear at the retarded time on either side of the origin.     

Effect of nonstationary thermal gravitation-capillary convection on temperature distribution in a thin vertical wall

Time dependences of temperature distributions in a thin metal wall were studied experimentally under two conditions of convective heat transfer in a tank model. In the first case, the vertical working wall was heated from within due to a convective heat flux from the opposite wall heated monotonously, and it was cooled due to heat transfer to the ambient medium. Dependence of the temperature field on a thin wall at the stage of convective flow development was retraced with the help of the thermographic camera and thermocouple sensors. In the second case, the tank wall was heated uniformly by IR radiation from the outside, and non-stationary convective flow and volumetric liquid heating were formed inside. Time dependence of temperature distribution over the wall height is studied. It is shown that the flow structure and convective heat transfer in a fuel layer with free boundary are subjected not only to the buoyancy force, but also to the thermocapillary effect. The local features of the flow affect temperature distribution in a thin wall.     

Analysis of an encapsulated whispering gallery mode micro-optical sensor

Whispering gallery mode (WGM) based micro-optical sensors are known to have higher sensitivity than fiber Bragg grating, Fabry–Perot, and microbend sensors. WGM sensors are created by optical coupling of a dielectric microparticle with an optical fiber. The combination of a microparticle and an optical-fiber to create the sensor requires encapsulating them in a suitable material so that the sensor can be used in practical applications. The sensitivity of the encapsulated sensors needs to be calibrated before they can be used. The present study conducts a parametric study to understand the effect of variables such as particle size and particle–fiber distance on the sensitivity of the encapsulated WGM sensors. Solid and hollow microparticle based sensors are studied. In the case of hollow particles, their wall thickness effects are also characterized. Results show that despite small strain, change in the index of refraction of the particle material due to the applied force contributes significantly in determining the sensitivity of these sensors.     

跨音速轴流压气机级三维粘性流场全工况数值模拟

采用一种快速求解三维粘性流场的计算方法求解跨音速轴流压气机级内部流场及全工况特性。该方法以LU-SGS-GE隐式格式和MUSCL TVD迎风格式为基础,结合壁面函数方法和简单的混合长度湍流模型,对三维可压缩雷诺平均Navie-Stokes方程进行求解。叶列间参数的传递采用混合平面方法并应用了微机网络并行计算技术。计算得到了NASA 37号低展弦比、跨音速轴流压气机级70％设计转速下的全工况性能曲线,并重点分析了其中一些典型工况下的内部流场。计算与实验结果的对比表明此方法能快速得到三维粘性流场的流动特性且计算精度较高,可用来模拟跨音速轴流压气机级内的全工况三维粘性流动。     

井外溶洞储层的偶极横波反射特征研究*

溶洞型储层是油气田中比较典型的储层之一,其非均质性强,勘探开发难度较大,偶极横波远探测技术是目前探测井外溶洞的有效方法。碳酸盐岩溶洞模型正演模拟对于现场的油气勘探和资料解释具有指导性作用。该文建立了几种比较典型的溶洞模型,并通过有限差分方法对溶洞储层的偶极三维反射声场进行了研究,发现在小源距范围内可以接收到来自溶洞后壁较强的反射波,随着源距的增大,该反射波逐渐减弱至消失;对于缝洞结合体的反射波场,来自裂缝的反射波能量要强于来自溶洞的反射波,且来自裂缝的反射波会掩盖溶洞前壁的反射波信息,这对后期的成像处理带来了困难。最后进一步研究了偶极远探测技术在溶洞方位识别以及尺寸大小估算中的应用。     

1.5级跨音速压气机内部流场数值分析

本文以正在建设的1.5级跨音压气机试验台所采用的压气机为研究对象,利用NUMECA软件计算了该压气机在不同转速下的特性曲线,并在设计转速下,对其内部流场进行了分析研究.研究表明:激波位置和强度随压气机运行工况的变化而变化;在近失速工况和堵塞工况时,压气机内部流动出现分离;在设计工况时,压气机内部流动状况良好.上述结论,可以为试验台建设中,探头位置的确定和激光测窗位置的选取等提供指导和帮助.此外,该算例作为一盲解,将来同实验结果对比后,可以用来检验和校准CFD程序,为国内F级燃机设计平台的建设打下良好的基础.     

使用确定应力模型研究离心压气机叶片相互作用

离心压气机叶轮和扩压器叶片间空隙很小,在无叶区和半有叶区的流动非定常特性十分明显。特别是离心叶轮出口通常的射流／尾迹流动使得有叶扩压器进口在时间、空间两个尺度上都存在十分强烈的不均匀性。叶轮和扩压器叶片间的相互作用,历来都被认为是影响离心压气机效率和稳定工作范围的重要因素。本文引入确定应力模型和改进的计算域延伸方法,计算了Ｋｒａｉｎ离心压气机组的流场,着重分析了叶轮出口无叶区、半无叶区等叶片间相互作用最强烈的区域的复杂流动现象。     

温度传感器(PT-100)安装方式实验

提出了热电阻温度计 (铂电阻 )温度传感器 (感温元件 )安装的实验模型。就几种温度传感器的安装方式进行了时间常数的测试 ,并比较几种安装方式的优缺点 ,以此作为 HT-7U螺杆压机站温度传感器安装的依据