航天飞机的低密度效应——(航天飞机空气动力学问题之三)

美国第一代航天飞机(Shuttle-I)在177千米高度以上飞行时处于自由分子流区(克努曾数 Kn≥10),在83～177千米的高度范围内处于过渡流区(0.001≤Kn≤10)。传统的连续介质空气动力学已不适用了,而要用非连续的稀簿空气动力学。本文简要介绍美国航天飞机研制过程中采用过的蒙特卡罗直接模拟法、粘性激波层法和洛克希德工程计算等理论计算方法。并与风洞试验和飞行试验结果进行了比较和分析。研究结果表明:低密度效应对航天飞机的气动加热、阻力系数和升阻比等气动性能有很大的影响;理论计算与飞行试验的差别随 K_n 数的增大而增大,其差別的原因尚没有确切和满意的解答。对过渡流,目前无论是理论计算还是风洞实验都存在着较大困难。因此必须加强对航天飞机低密度效应的理论和实验研究。     

航空、航天类中文核心期刊《实验流体力学》征稿简则

1．《实验流体力学》（原名：《流体力学实验与测量》（季刊），是中国空气动力学会主办的综合性学术兼技术刊物。主要传递实验流体力学以及空气动力学相关领域的新信息，新成果和新动态。主要的读者对象是：从事实验流体力学、空气动力学及其相关学科的实验技术、实验研究、测试技术与设计、制造、使用、教学等领域的广大科技人员、管理人员和院校师生。     

NOVEL RADAR SIGNAL SORTING METHOD BASED ON GEOMETRIC COVERING

With the increase of complexity of electromagnetic environment and continuous appearance of advanced system radars, signals received by radar reconnaissance receivers become even more intensive and complex. There- fore, traditional radar sorting methods based on neural network algorithms and support vector machine （SVM） cannot process them effectively. Aiming at solving this problem, a novel radar signal sorting method based on the cloud model theory and the geometric covering algorithm is proposed. By applying the geometric covering algo- rithm to divide input signals into different covering domains based on their distribution characteristics, the method can overcome a typical problem that it is easy for traditional sorting algorithms to fall into the local extrema due to the use of complex nonlinear equation to describe input signals. The method uses the cloud model to describe the membership degree between signals to be sorted and their covering domains, thus it avoids the disadvantage that traditional sorting methods based on hard clustering cannot deinterleave the signal samples with overlapped param- eters. Experimental results show that the presented method can effectively sort advanced system radar signals with overlapped parameters in complex electromagnetic environment.     

纵向尾流间隔计算方法研究

综合考虑了飞机的速度、翼展、机翼面积、发动机推力等参数,应用空气动力学中的环量计算理论、尾流消散原理等,将动量定理和涡阻力的计算原理应用到尾流间隔的计算,分别建立了纵向尾流间隔计算模型。采用实际数据计算验证模型的正确性。     

DYNAMIC RESPONSE ANALYSIS OF CARRIER-BASED AIRCRAFT DURING LANDING

In view of the complexity of landing on the deck of aircraft carrier, a systematic model, composed of six- degree-of-freedom mathematic model of carrier-based aircraft, four-degree-of-freedom model of landing gears and six-degree-of-freedom mathematic model of carrier, is established in the Matlab-Simulink environment, with damping function of landing gears and dynamic characteristics of tires being considered. The model, where the car- rier movement is introduced, is applicable for any abnormal landing condition. Moreover, the equations of motion and relevant parameter are also derived. The dynamic response of aircraft is calculated via the variable step-size Runge-Kuta algorithm. The effect of attitude angles of aircraft and carrier movement during the process of landing is illustrated in details. The analytical results can provide some reference for carrier-based aircraft design and main- tenance.     

四川海特：全面发展续写辉煌

近年来，海特高新在巩固原有维修能力的同时，不断拓展新业务，极大地增强了自身的市场竞争力。今年，旗下的奥特附件空气压缩站扩容改造工程顺利完工，使其空调气动附件维修能力上了一个新的台阶，基本町满足宽体双发飞机空气循环机（ACM）、空气起动机等气动附件的维修需求。     

科学大争论——以太是不是真的存在?(上)

<正>以太在希腊语里的意思是"上天的空气",在古希腊神话中,指天神呼吸的纯净空气,与凡人呼吸的下层浑浊空气不同。哲学家也喜欢"上天的空气"。古希腊哲学家认为世界由水、气、火、土四种元素组成。特别看重几何学的柏拉图把四种元素几何化,认为组成它们的原子