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为指导全流量补燃循环发动机推力室全尺寸气气喷注器设计,采用气氢/气氧推进剂,在带可视化窗口的燃烧室中开展了气气燃烧流场相似性缩尺试验研究。采用高速摄影仪获得了不同流量工况下,同轴剪切喷嘴稳定燃烧和不稳定燃烧两种状态下近喷嘴区域的燃烧火焰结构,并分析了不稳定燃烧的频率特性。结果表明:在保持推进剂种类、推进剂混合比、推进剂温度、燃烧室及喷嘴结构尺寸不变的情况下,随着喷嘴流量的逐步增大,稳定燃烧和不稳定燃烧的喷嘴出口火焰结构均有一定的相似性,且不稳定燃烧的频率相同。 相似文献
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在室内WiFi环境下,针对常见指纹匹配算法所忽略的信号波动问题,提出了一种基于自适应修正曼哈顿距离和AP选择的指纹匹配算法,并结合加权K近邻方法实现定位。首先采用AP选择算法获取部分受干扰程度小和出现频率高的AP,在指纹匹配时仅使用该部分AP的接收信号强度进行计算;在分析WiFi信号传播衰减公式和信号波动的基础上,提出了将自适应修正曼哈顿距离作为指纹匹配的度量距离,使用该距离旨在平滑信号波动对指纹相似度计算的影响;最后采用加权K近邻方法估计测试点的坐标。实验结果表明,在加权K近邻方法的框架下,基于自适应修正曼哈顿距离的定位算法在定位精度上优于基于欧氏距离、曼哈顿距离、余弦距离和Sorensen距离的定位算法。 相似文献
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就风洞尺寸要多大才比较合理以及小风洞的改造和挖潜等问题进行了讨论。认为风洞尺寸不是越大越好,而是在不同速度范围存在着一组相对适中的带某种唯一性的风洞尺寸。这种风洞尺寸,既能满足航天器研制的需要,又具有合理的经费开支。文中推荐了不同速度下一组较合适的且能满足需要的风洞尺寸,供人们参考。同时本文还认为,在一定的风洞条件下,实验数据的精准度与风洞尺寸的大小无关,只要相似模拟的条件正确,就能给出同样精准度的实验数据。就这一观点,列举了在北京空气动力研究所的FD 02小风洞中做出的几种实验。 相似文献
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As one of the promising configurations of the next generation of commercial aircraft,research on departure characteristics of the Blended-Wing-Body(BWB) is of great signification to safe flight limits. A three-degree-of-freedom(3-DOF) virtual flight test in a wind tunnel has been implemented for a candidate configuration to predict the departure characteristics. The support mechanism, the test model and the control law of the virtual flight test are introduced. In order to show the relationship ... 相似文献
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《中国航空学报》2020,33(7):1942-1952
Squealer tip is widely used in turbines to reduce tip leakage loss. In typical turbine environment, the squealer tip leakage flow is affected by multiple factors such as the relative casing motion and the wide range of variable incidence angles. The development of experimental methods which can accurately model the real turbine environment and influencing factors is of great significance to study the squealer tip leakage flow mechanism. In the present paper, a low-speed turbine cascade test facility which can model the relative casing motion and wide range of variable incidence angles (−25° to 55°) is built. Based on the similarity criteria, a high-low speed similarity transformation method of the turbine cascade is established by considering the thickness of the turbine blade. A combined testing method of Particle Image Velocimetry (PIV) and local pressure measurement is proposed to obtain the complex flow structures within the tip cavity. The results show that the experimental method can successfully model the relative casing motion and the wide range of variable incidence angles. The low-speed cascade obtained by the similarity transformation can model the high-speed flow accurately. The measurement technique developed can obtain the complex flow field and successfully capture the scraping vortex within the squealer tip. 相似文献
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