氟化处理工艺对TiAl合金氧化层组织的影响

文章研究了氟离子注入和NH₄F溶液处理对TiAl合金高温氧化层组织结构的影响规律。结果表明:TiAl合金高温氧化层的组织和致密度受氟化处理工艺和参数的影响很大;经过表面氟化处理的TiAl合金高温氧化抗力高于原始合金;随着表面氟含量增加,氧化层的钛元素含量增加,致密度下降,研究表明存在一个最佳的表面氟浓度。     

冲击载荷作用下38CrMoAl渗氮钢损伤机理和耐腐蚀性能

为研究38CrMoAl渗氮钢材料在冲击载荷与海洋环境侵蚀共同作用下的损伤机理和耐腐蚀性能,对渗氮处理前后的38CrMoAl钢材料进行了冲击加载试验和腐蚀性能测试。研究发现渗氮38CrMoAl钢材料在高应变率下具有较强的正应变率敏感性。在冲击载荷作用下,试件表面渗氮层出现裂纹,并伴随着渗氮层的部分脆性剥落,但裂纹长度均在500~700 μm,裂纹只在渗氮层中扩展,并没有继续延伸至非渗氮层的金属基体内部。渗氮处理提高了材料表面硬度和强度,但降低了韧性。电化学测试结果表明渗氮处理显著提高了材料的耐腐蚀性能,其自腐蚀电位相对于未渗氮试件由-726.24 mV正移至-174.42 mV。但冲击加载后的渗氮试件由于表面渗氮层的破损,部分金属基体露出并与未发生破坏的表面形成电势差,进而发生较为强烈的电偶腐蚀。扫描开尔文探针测试结果表明,渗氮件表面阴阳极电位差及电位分散程度相对于未渗氮件增大,渗氮件更易发生局部腐蚀。冲击加载改变了渗氮层的表面状态,阴阳极电位差增加,使材料表面腐蚀变得更加不均匀。对试件耐腐蚀性能进行了盐雾试验验证,盐雾试验结果与电化学测试分析结果相一致,在舰载机维护保养中,应关注受冲击部位渗氮层的裂纹检查,并做好相应的防腐处理。     

预处理特征型边界条件及其回流处理技术

通过特征型预处理Euler方程推导出预处理特征型的边界条件处理方法,并发展了预处理的回流处理技术,增强计算的鲁棒性和精度。通过特征型预处理Euler方程的特征关系得到边界条件处理方法;在亚声速速入口和出口边界,根据其特征方程确定回流边界处理方法。通过数值模拟发现:带回流的特征型边界处理方法比Turkel方法收敛快1.5倍以上,而计算精度与SIMPLE方法相当;在出口带有回流的计算中,其压力误差比Fluent降低68.3%。由此可知带有同流处理的特征型边界处理方法具有较高的鲁棒性和精度,在实际的工程计算中有一定的应用价值。     

基于CCD和超声的物体位姿检测方法及精度分析

介绍了用单个CCD摄像机和超声传感器相结合检测物体位姿的方法.首先由CCD摄像机采集一幅图像,获取物体上目标点在图像坐标系中的理想坐标,并由此确定该点投影矢量(连接物体点和对应图像点的直线)的方向;然后控制机器人运动,使超声传感器的z轴与求得的投影矢量重合;最后用超声传感器测出投影矢量的长度,确定目标点在摄像机坐标系中的坐标.分析了影响检测精度的主要因素,具体研究了超声传感器的安装参数对检测精度的影响规律,进行了仿真分析.该方法可以有效地降低图像处理所带来的巨大数据量,避开双目视觉中的图像匹配问题,快捷、精确检测物体的位姿.     

大弯角开槽叶栅槽道位置与结构研究

为拓宽大弯角扩压叶栅可用攻角范围,优化叶片吸力面流动分离结构,本文以一大弯角叶栅为研究对象,对叶片采用压力面到吸力面打通的双“C”型槽道结构处理,在保持槽道长度及其他参数不变的条件下,设置85%、80%、75%、70%轴向弦长四个出口位置研究槽道出口位置对叶栅性能的影响。研究发现,特定攻角下,槽道出口位于吸力面角区分离线起始点之后、尾缘分离线之前,对吸力面流动分离的控制效果较佳;在全攻角范围,槽道出口则取在0o攻角对应较佳出口位置为好。为减小槽道内总压损失,本文提出了一种“SC”型槽道改进结构,在80%轴向弦长槽道出口位置处与双“C”型槽道以及原型叶栅进行对比。结果表明,“SC”型槽道结构相比于双“C”型槽道结构,叶栅尾迹损失及槽道内总压损失减少,槽道出口射流速度提高,叶片尾缘处静压升高;相比于原型叶栅则能有效降低其在全攻角范围内的总压损失,基本消除叶片吸力面附面层分离,削弱角区分离,提高叶栅的扩压能力。     

空间碎片撞击气瓶穿孔孔径预测公式研究

星上压力容器中储存有高压气体或液体,在受到空间碎片和微流星体超高速撞击时可能发生灾难性事故。文章采用均匀实验设计方法对星上常用高压气瓶的超高速撞击仿真方案进行了试验设计,并通过LS-DYNA仿真软件对其进行了超高速撞击数值仿真,获取了不同参数的弹丸撞击气瓶时气瓶器壁穿孔孔径。通过对器壁穿孔孔径的数据拟合,建立了无防护情况下气瓶器壁的穿孔孔径预测公式。与试验结果对比表明,建立的穿孔孔径预测公式具有一定的预测精度。     

提高航天器超声检漏灵敏度的方法研究

应用超声进行航天器舱体及管道系统检漏是一种可快速定位漏点的无损检测方法,从试验方法及信号处理上可以有效提高各种工况下的检漏灵敏度。文章对非接触超声检漏提高有效湍流强度增强超声信号和接触超声检漏改变信号带通频率这两种方法进行了试验研究。结果显示,采用这两种方法均能增强有效信号强度,提高检漏灵敏度。     

优化镍基高温合金X-750热处理工艺参数的非线性超声无损评估方法

为了获得更好的材料性能,需要对热处理工艺参数进行精确地优化。非线性超声无损检测技术是一种可以有效表征材料微观结构状态变化的评估方法,可以用来评估、优化热处理工艺参数。利用非线性超声波对热处理后的X-750合金材料进行评估,根据超声传播的非线性响应不同,对材料的性能变化做出判断,并与线性超声检测技术的评估结果进行了对比研究。研究发现经过热处理之后,材料性能显著提高,在其中传播的超声非线性响应则明显下降。材料经过热处理后性能提升越大,其声学非线性响应就会变得越小。根据超声波传播的非线性响应定性评估了3种不同的热处理工艺,明确了最优的镍基高温合金X-750退火工艺参数。研究证实了非线性超声方法的敏感度优于传统的线性超声评估方法,可以对材料的热处理效果进行无损评估,从而对热处理工艺参数进行优化与完善。     

Response and stabilization of a two-stage axial flow compressor restricted by rotating inlet distortion

This paper considers effects of Rotating Inlet Distortion (RID) on a two-stage axial compressor and the stabilization effects of a casing treatment subjected to the considered RID. In multi-spool engines, the downstream compressor suffers a RID when the upstream fan/compressor is in rotating stall. A controlled rotating sectional screen upstream of the compressor was adopted to generate the RID in different intensities, and co- or counter spinning direction compared with the rotor. The response of the compressor to inlet distortion was interpreted as the changes of stall margin. Results show that there are two peaks for the stall margin degradation where the distortion screen rotates near 20% and 70% of the rotor’s rotational frequency, respectively. Based on the measurements taken during the pre-stall process, it is suggested that the two frequencies are associated with the eigen frequencies of the compressor. Specifically, the first is associated with a stall precursor that is suspected as an initial disturbance existing in compressor and the second is related to a spike-type stall precursor. At last, a kind of Stall Precursor-Suppressed (SPS) casing treatment was applied to enhance the compressor stability in RID conditions. The result indicates that the stall margin is improved by 6% at an average level and there is nearly no efficiency loss caused by the application of such casing treatment.     

Numerical simulation of a UAV impacting engine fan blades

A 3D digital model of a small Unmanned Aerial Vehicle (UAV) is obtained by using the method of scanning reverse modeling and joint mapping. A numerical simulation of a small UAV strikes on rotary engine blades, presented in this paper, was performed with a Transient Nonlinear Finite Element code PAM-CRASH software. A test of motor strike on plate was developed and the dynamic response of the plate were obtained to validate the numerical simulation method of a UAV strike on blades. Based on this, dynamic damage response caused by UAV on the engine blades were studied. It is indicated that the impact process between the UAV and a single blade can be divided into two typical stages: cutting and impact. Cutting mainly leads to the failure of the leading edge material, and impact mainly leads to the plastic deformation of the blade. At the same time, it is compared with the damage impacted by bird with the same mass. For the same mass of bird and UAV, the damage caused by UAV striking fan blade is more serious, and 1.345 kg UAV striking fan blade of typical civil aviation engine is enough to cause damage to flight safety.