The evolution of mirror type magnetic fluctuations in the magnetosheath based on multipoint observations

Two orbits were selected in January–February 2006 when the separation between the Cluster spacecraft was large and mirror type magnetic field fluctuations were observed by all spacecraft in different regions of the terrestrial magnetosheath. Minimum variance analysis was applied to find the mirror type fluctuations, and the amplitude of the fluctuations was determined individually. Mirror mode structures are moving along the streamlines frozen in the plasma. A model was developed for the calculation of plasma flowtime from the bow shock to the observation point. The growth rate of the field strength perturbations was estimated by comparing the amplitudes of fluctuations observed simultaneously at distant locations (∼10,000 km) based on the assumption that δB ∼ exp(γt). The obtained growth rate values were about an order of magnitude smaller than those provided by linear models and they decreased in the inner regions of the magnetosheath, indicating some saturation in the growth of the waves when proceeding towards the magnetopause. The results of these two case studies suggest that mirror type fluctuations originate from the compression region downstream of the quasi-perpendicular bow shock, and the growth of the fluctuations cannot be described by linear approximations.     

A Structured Mesh Euler and Interactive Boundary Layer Method for Wing/Body Configurations

To compute transonic flows over a complex 3D aircraft configuration, a viscous/inviscid interaction method is developed by coupling an integral boundary-layer solver with an Eluer solver in a ＂semi-inverse＂ manner. For the turbulent boundary-layer, an integral method using Green＇s lag equation is coupled with the outer inviscid flow. A blowing velocity approach is used to simulate the displacement effects of the boundary layer. To predict the aerodynamic drag, it is developed a numerical technique called far-field method that is based on the momentum theorem, in which the total drag is divided into three component drags, i.e. viscous, induced and wave-formed. Consequently, it can provide more physical insight into the drag sources than the often-used surface integral technique. The drag decomposition can be achieved with help of the second law of thermodynamics, which implies that entropy increases and total pressure decreases only across shock wave along a streamline of an inviscid non-isentropic flow. This method has been applied to the DLR-F4 wing/body configuration showing results in good agreement with the wind tunnel data.     

增升状态下的全机位流数值模拟

研究了势流理论下的全机增升装置复杂外形气动力数值计算方法,该方法以低阶面元法为基础,具有计算量小、速度快的优点.复杂流动的粘性效应主要通过附面层粘性修正技术加以体现.采用该方法对某增升装置翼身组合体外形压力分布特性进行计算,并和风洞实验数据相比较,验证了方法的正确性和实用性.在此基础上对某型飞机真实复杂外形的压力分布特性进行了计算,为复杂外形飞行器增升装置的初步设计、方案选型与评估提供了非常理想的工程技术手段.     

Stationary flow fields prediction of variable physical domain based on proper orthogonal decomposition and kriging surrogate model

In this paper a new flow field prediction method which is independent of the governing equations, is developed to predict stationary flow fields of variable physical domain. Predicted flow fields come from linear superposition of selected basis modes generated by proper orthogonal decomposition(POD). Instead of traditional projection methods, kriging surrogate model is used to calculate the superposition coefficients through building approximate function relationships between profile geometry parameters of physical domain and these coefficients. In this context,the problem which troubles the traditional POD-projection method due to viscosity and compressibility has been avoided in the whole process. Moreover, there are no constraints for the inner product form, so two forms of simple ones are applied to improving computational efficiency and cope with variable physical domain problem. An iterative algorithm is developed to determine how many basis modes ranking front should be used in the prediction. Testing results prove the feasibility of this new method for subsonic flow field, but also prove that it is not proper for transonic flow field because of the poor predicted shock waves.     

一种双钟型喷管液氧/甲烷发动机系统方案

根据双钟型喷管高度补偿特点及技术研究现状,提出了一种双钟型喷管液氧甲烷发动机系统方案,进行了双钟型喷管基弧段及延伸段面积比优化,并与其他系统方案进行了性能对比分析。研究表明,对于地面起动的芯级发动机,采用双钟型喷管是提高发动机综合比冲性能以及运载器有效载荷的有效途径。     

金属密封件镀金工艺研究

介绍了金属密封件镀金工艺技术,该工艺采用亚硫酸盐镀金方案,以单脉冲电源为镀覆电源,以预镀镍层为中间镀层来制备金镀层,得到了结晶细致、厚度均匀并与基体上结合牢固的金镀层.研究了金镀层的沉积速率和结合强度,观察了镀层的表面形貌和组织结构,进行了金属密封件气密性试验和典型试验.结果表明：金属密封件金镀层的技术性能指标满足设计要求,能够应用于液体火箭发动机中,该发动机已通过地面热试车考核.     

220GHz返波振荡器高频特性及互作用研究

文章对220GHz折叠波导慢波电路的返波传输特性进行了研究。介绍了返波振荡器的工作原理,结合模拟仿真和理论分析,针对220GHz的返波振荡器,研究各个参数对冷特性的影响。对220GHz返波振荡器的高频结构进行了初步设计,给出了结构参数以及相应的模拟结果。结果表明在不考虑损耗的情况下,设计的结构可以在中心频率220GHz处获得约为0．5W的功率,可调谐范围是30GHz,调谐电压范围为5．5kV-12kV。     

载人航天器空气环境参数控制非定常仿真分析

为支持乘员在轨驻留,载人航天器需通过空气环境控制系统将众多设计参数和空气环境参数控制在指标范围内。文章建立了一种载人航天器空气环境非定常控制仿真分析模型,包括舱体模块、航天员模块、舱压控制模块、温湿度控制模块以及CO2净化模块。利用该模型分析了载人航天器空气环境参数随乘员代谢水平的非定常变化趋势,并评估了控制系统的工作性能。结果表明:乘员代谢水平变化对空气环境参数有显著影响,通过调节控制系统运行参数可将各空气参数控制在有效指标范围内。人区温度与O2分压、CO2分压和人区湿度有密切的影响关系,不可孤立地进行分析。为载人航天器空气环境参数控制系统的设计和流程改进提供了依据。     

微纳米尺度流动实验研究的问题与进展

微纳米实验流体力学研究的流动特征尺度在1mm～1nm范围,处于宏观流动到分子运动的过渡区。连续介质力学与量子力学这两个经典理论的衔接,提出了诸如连续性假设适用性、边界滑移等基本理论问题。同时从微纳米尺度研究界面处液/固/气的耦合,化学、电学性质对流动的影响值得关注。微纳米实验测量仪器融入了力、电等测量手段,要求测量空间精度达到nm量级,力的测量精度达到pN,时间分辨率达到ns。本文围绕连续性假设适用性、边界滑移、微纳米粒子布朗运动及微尺度涡旋测量等问题,介绍了 Micro/Nano PIV、示踪粒子流场显示等技术应用于微纳流场观测的进展与难点。目前微纳米流动测量仍然沿着经典流体力学测量“小型化”的思路开展,而纳尺度的测量期待着新的实验方法与技术的提出。     

超声速条件下多体干扰与分离试验研究

采用根据国外公开文献设计的类CAV模型,在0．6m×0．6m 跨/超声速风洞中开展了多体干扰与分离网格测力试验研究,初步获得了典型多体飞行器分离过程中的气动特性变化规律。试验结果表明,载荷模型气动特性受分离位置变化影响非常明显。载荷模型沿轴向分离时,气动力（矩）逐步接近自由流中气动力（矩）值,载荷模型法向位置改变会引发其气动力（矩）值发生更为剧烈的变化。引发这种现象的原因有两个：一是尾迹和头激波的发展改变了不同轴向位置处载荷模型的表面流态,从而影响了其气动特性;二是母机模型底部流动具有明显的非对称膨胀特征,不同法向位置处流速大小和方向差异明显,导致载荷模型气动特性随法向位置变化更为剧烈。