Standing window of oblique detonation with pathological behaviour

Standing of an Oblique Detonation Wave (ODW) on a wedge within combustor is the prerequisite of thrust generation for ODW engine which is regarded as a novel and conceptual propulsion device with hypersonic flight Mach number. Usually a standing window of ODW is defined as the wedge angle ranged from the ODW detached angle from wedge (upper limit) to the angle that a Chapman-Jouguet (CJ) detonation occurs (lower limit). For pathological detonation cases, however, the CJ detonation cannot be achieved, and thus the lower limit of the standing window of ODW should be revisited. In present study, two types of reactions in hypersonic incoming flow that include the behavior of pathological detonation, that is, the single-step irreversible reaction with mole variation and the two-step irreversible reactions with exothermic process followed by endothermic process, have been used for studying standing behavior of ODW. The steady detonation polar analysis of ODW is carried out for both reaction systems. The results reveal that the reaction with more mole decrement and the reactions with stronger endothermic process show the pathological detonation feature and therefore modify the lower limit of standing window of ODW. Three equivalent parameters are proposed to quantitatively measure the standing window range of ODW from points of view of thermodynamics, Mach number of incoming flow and heat effect of reactions. It is found that the standing window of ODW is determined by the specific heat ratio, the overdrive degree of detonation and the endothermic level of the hypersonic incoming flow, regardless of whether the detonation is pathological or not.     

Re-entry trajectory tracking of reusable launch vehicle using artificial delay based robust guidance law

A Reusable Launch Vehicle (RLV), during the re-entry phase of its flight, experiences uncertain environment and extreme turbulence. This calls for an effective control strategy to guide the vehicle efficiently on a trajectory that allows safer landing conditions while providing robustness against external disturbances and system uncertainties. In this regard, a Time-Delayed Control (TDC) strategy has been proposed to track the space vehicle on a predetermined trajectory in the presence of these uncertainties. In the proposed approach, the system vector and the uncertainties are lumped into a single function which is estimated using the input and output data from the previous instant. Theoretical analysis of the control strategy executed using Lyapunov’s method, proves Uniformly Ultimately Bounded (UUB) stability of the closed loop system. The efficacy of the proposed approach has been verified through simulation studies which affirm robust tracking of the optimal trajectory generated through Pseudo-Spectral method (PSM), in the presence of time-varying uncertainties.     

一种定量空战决策方法

提出了一种定量空战决策方法,以空空导弹的攻击区与发射条件为基础,通过定义空战态势指标函数,定量描述空战态势.根据空战态势指标函数值和中远程空战以及近距空战的特点决定采取的机动策略,将空战机动策略与当前空战状态变量之间的关系建立起来,使得从空战决策的前因定量计算空战策略的后果成为可能.空战整个过程的分析、评估、决策、机动等环节都是定量进行.建立了战机、目标机、导弹和决策模块的数学模型,给定不同的初始条件,对空战过程进行了仿真,分别验证了中远程空战决策和近距空战决策的有效性.     

基于成本考虑的天地往返技术途径分析

采用能量分析方法,对天地往返成本的影响因素进行了分析。重点对入轨方式、发射方法和动力系统等因素进行了分析。提出了未来天地往返运输技术的研究设想。     

Variable slip window technology in transition detection on pitching airfoil

In the pitching motion, the unsteady transition and relaminarization position plays an important role in the dynamic characteristics of the airfoil. In order to facilitate the computer to automatically and accurately calculate the position of the transition and relaminarization, a Variable Slip Window Technology (VSWT) suitable for airfoil dynamic data processing was developed using the S809 airfoil experimental data in this paper and two calculation strategies, i.e., global strategy and single point strategy, were proposed: global strategy and single point strategy. The core of the VSWT is the selection of the window function h and the parameters setting in the h function. The effect of the VSWT was evaluated using the dimensionless pulse strength value (INB), which can be used to evaluate the signal characteristics, of the root mean square (RMS) value of the fluctuating pressure. It is found that: the h function characteristics have a significant influence on the VSWT. The suitable functions are H_n function constructed in this paper and step function. For the left boundary of the magnified area, the step function can obtain the largest INB value, but the robustness is not good. The H₁ function (Gaussian-like function, n = 1) can show higher robustness while ensuring a large INB value. The two computing strategies, which are single point strategy and global strategy, have their own advantages and disadvantages. The former strategy, that is the single point strategy, can achieve a higher INB value, but the RMS magnification at the feature position needs to be known in advance. Although the INB value obtained by the latter strategy, that is the global strategy, is slightly smaller than the calculation results of the former strategy, it is not necessary to know the RMS magnification at the feature position in advance. So the global strategy has better robustness. The experimental data of NACA0012 airfoil was used to further validate the developed VSWT in this paper, and the results show that the VSWT developed in this paper can still double the INB value of the transition/relaminarization position. The VSWT developed in this paper has certain practicability, which is convenient for the computer to automatically determine the transition/relaminarization characteristics.     

固液混合火箭发动机研究进展

固液火箭发动机因其推进剂能量较高、安全性好、易实现推力调节、可实现多次启停、药柱稳定型好、温度敏感性低、环保性佳和经济性好的特点,十分符合下一代航天平台绿色环保、智能随控、快速响应的发展需求,在探空火箭、亚轨道飞行器、靶标、小型运载火箭、助推器、上面级动力系统、姿轨控动力系统、着陆器和其他许多民用商业航天领域中都具有良好的应用前景。分析了固液火箭发动机的国内外发展现状及发展趋势,对国内外固液火箭发动机相关的典型项目、工程应用和关键技术发展情况进行了回顾和总结,并以此为基础总结固液火箭发动机技术的发展趋势和有待进一步突破的关键技术。     

航空精密工件电火花加工微型方窗口研究

在电火花加工中,零件参数的选择对加工工艺指标起着重要作用,只有正确选择电参数才能加工出品质优良的产品。影响电参数选择的因素主要有:电极材料、工件材料、放电面积、表面粗糙度、放电间隙、电极损耗和加工速度等。主要针对微型方窗口的加工确定电极材料、放电间隙、加工速度等电参数,并对上述分析方法进行延伸扩展。     

基于凸优化的再入轨迹三维剖面规划方法

可重复使用飞行器一般采用大升阻比气动外形，再入轨迹三维剖面规划方法可充分发挥这类飞行器固有的机动能力。计算量大是制约三维剖面规划应用的难题，为提高计算效率，提出了一种基于凸优化的再入轨迹三维剖面规划方法。首先，分析运动方程特性，利用定义新的控制变量、约束松弛、连续线性化等技术，将原始非凸的三维剖面规划问题转化为一个凸优化问题。其次，将指令反解步骤嵌入至序列凸化算法中，通过迭代求解凸优化子问题，获得原问题的可行解。数值仿真结果表明所提方法具有较高的求解精度和确定的收敛性质，飞行器的机动能力得到充分发挥；与伪谱法的结果对比表明凸优化方法在轨迹规划问题上具有更高的求解效率。     

运载火箭动力系统试验承力环的静力试验

建立了某型号运载火箭动力系统试验用承力环的非破坏性静力试验方案,以评估该承力环的强度和刚度。为模拟发动机关机时的载荷冲击,将静力试验最大载荷设定为发动机额定总推力的2倍,包含水平和垂直两个分量,均分为8个载荷步加载。在承力环上设置了27个三向应变测点和12个轴向位移测点,以监测一些关键点的应力和位移。测量结果显示,在最大载荷下,当量应力达到303 MPa,低于材料屈服强度;轴向变形达到3.16 mm,低于设计许用变形;应力最大点位于支腿销孔处。对销孔孔距的变化进行了测量,并对附近的钢板表面进行了MT探伤。数据结果表明,该承力环在两倍的动力系统试验额定载荷下有足够的强度和刚度,可用于该试验。     

碎裂开盖鱼雷发射箱内流场变化研究

利用计算流体力学的仿真软件FLUENT对鱼雷发射箱内流场变化情况进行仿真计算,通过仿真计算分析发射箱内的压强分布规律及其对易碎裂盖体的影响。仿真结果表明,后盖在助推器射流直接冲击下会受到极不均匀的压强作用,可能使后盖中心破裂而不碎;前盖受后盖反射的射流影响而开盖。研究结果对发射箱的碎裂开盖方案设计有一定的指导意义。