Computational aerodynamic analysis on perimeter reinforced （PR）-compliant wing

Abstract Implementing the morphing technique on a micro air vehicle （MAV） wing is a very chal- lenging task, due to the MAWs wing size limitation and the complex morphing mechanism. As a result, understanding aerodynamic characteristics and flow configurations, subject to wing structure deformation of a morphing wing MAV has remained obstructed. Thus, this paper presents the investigation of structural deformation, aerodynamics performance and flow formation on a pro- posed twist morphing MAV wing design named perimeter reinforced （PR）-compliant wing. The numerical simulation of two-way fluid structure interaction （FSI） investigation consist of a quasi- static aeroelastic structural analysis coupled with 3D incompressible Reynolds-averaged Navier- Stokes and shear-stress-transport （RANS-SST） solver utilized throughout this study. Verification of numerical method on a rigid rectangular wing achieves a good correlation with available exper- imental results. A comparative aeroelastic study between PR-compliant to PR and rigid wing per- formance is organized to elucidate the morphing wing performances. Structural deformation results show that PR-compliant wing is able to alter the wing＇s geometric twist characteristic, which has directly influenced both the overall aerodynamic performance and flow structure behavior. Despite the superior lift performance result, PR-compliant wing also suffers from massive drag penalty, which has consequently affected the wing efficiency in general. Based on vortices investigation, the results reveal the connection between these aerodynamic performances with vortices formation on PR-comoliant wing.     

脉冲爆震火箭发动机引射模态的起爆实验研究

为实现脉冲爆震火箭发动机(PDRE)引射模态下主爆震室的起爆,采用航空煤油和氧气作为推进剂,设计了PDRE引射模态的模型机,采用压电传感器测量主爆震室中爆震波的压力和速度.在主爆震室中成功实现了5 ～8Hz稳定连续的爆震,爆震波的峰值压力能够达到3MPa,爆震波以1600～ 2000m/s左右的速度在主爆震室中传播.实验结果表明:PDRE引射模态下主爆震室的DDT距离,远低于常规高能电喷起爆下的两相PDRE的DDT距离;高频PDRE引射模态下主爆震室的起爆难度加大;加长主爆震室、末端增加收敛段可以提高引射模态的爆震性能.     

驻涡燃烧室驻涡区涡系特点数值模拟

为深入了解驻涡燃烧室凹腔内流场的涡系分布特性,采用FLUENT对不同驻涡区前进口堵塞比和不同燃烧室入口速度的驻涡区流场进行计算,分析典型截面压力场和流线图,研究驻涡区涡系特点.结果表明:不同纵截面旋涡特点不同,主流被联焰板堵塞的凹腔纵截面只有主涡,为稳定点火和火焰稳定提供条件;不同横截面的旋涡差别较大,离驻涡区前壁越远的截面涡心距越大,贴近前壁和后壁的截面均无旋涡;燃烧室入口速度对轴向中间截面的旋涡结构无影响,而前进口堵塞比对旋涡结构影响较大.     

航空发动机排气喷管红外辐射特征数值研究

红外隐身技术对提高未来战机战场生存力具有重要意义,发动机排气系统是飞机后半球的主要红外辐射源。为了研究涡扇发动机排气喷管的红外辐射特性,采用与成熟商用CFD软件相结合的策略,基于离散传递方法,自主开发航空发动机排气系统红外辐射特征数值计算软件。提出一种射线行程追踪方法,用来提高软件计算效率和模拟精度;最后用该软件对某型涡扇发动机排气系统收缩喷管及两种采用不同红外抑制措施的喷管进行数值模拟研究。结果表明：相对于传统的收缩喷管,二元喷管能够在绝大部分探测方向上有效降低喷管的红外辐射,引射喷管可在大角度探测方向上起到显著的红外隐身效果。     

MIDACO on MINLP space applications

A numerical study on two challenging mixed-integer non-linear programming (MINLP) space applications and their optimization with MIDACO, a recently developed general purpose optimization software, is presented. These applications are the optimal control of the ascent of a multiple-stage space launch vehicle and the space mission trajectory design from Earth to Jupiter using multiple gravity assists. Additionally, an NLP aerospace application, the optimal control of an F8 aircraft manoeuvre, is discussed and solved. In order to enhance the optimization performance of MIDACO a hybridization technique, coupling MIDACO with an SQP algorithm, is presented for two of these three applications. The numerical results show, that the applications can be solved to their best known solution (or even new best solution) in a reasonable time by the considered approach. Since using the concept of MINLP is still a novelty in the field of (aero)space engineering, the demonstrated capabilities are seen as very promising.     

A point-wise least squares spectral analysis (LSSA) of the Caspian Sea level fluctuations,using TOPEX/Poseidon and Jason-1 observations

The Caspian Sea has displayed considerable fluctuations in its water level during the past century. Knowledge of such fluctuation is vital for understanding the local hydrological cycles, climate of the region, and construction activities within the sea and along its shorelines. This study established a point-wise satellite altimetry approach to monitor the fluctuations of the Caspian Sea using a complete dataset of TOPEX/Poseidon for the period 1993 to the middle of 2002, and its follow-on Jason-1 for the period 2002 to August 2009. Therefore, 280 virtual time-series were constructed to monitor the fluctuations. The least squares spectral analysis (LSSA) method is, then employed to find the most significant frequencies of the time-series, while the statistical method of principle component analysis (PCA) is applied to extract the dominant variability of level variations. The study also used the observations of TOPEX/Poseidon and Jason-1 over the Volga River along with 5 years of Volga’s water discharge to study its influence on the Caspian Sea level changes. The LSSA results indicate that the lunar semidiurnal (M2) and the Sun semidiurnal (S2) frequencies are the main tidal frequencies of the Caspian Sea with the mean amplitude of 4.2 and 2.8 cm, respectively. A statistically significant long-term frequency (12.5-years period) is also found from altimetry and tide gauge observations. A phase lag, related to the inter-annual frequencies of the Volga River was detected from the point-wise time-series showing level propagation from the northwest to the southeast of the sea. The cross-correlation between the power spectrum of Volga and that of the northern-most, middle, and southern-most points within the Caspian Sea were respectively 0.63, 0.51 and 0.4 of zero-lag correlation, corroborating the influence of the Volga River. The result of PCA also shows that different parts of the Caspian Sea exhibit different amplitudes of level variations, indicating that the point-wise approach, when employing all available satellite measurements could be a suitable method for a preliminary monitoring of this inland water resource as it gives accurate local fluctuations.     

利用CFD技术计算飞行器动导数

利用非定常流场数值计算方法模拟飞行器强迫俯仰振荡仅能得到俯仰力矩系数对迎角变化率和俯仰角速度的动导数之和,而动稳定性分析需要单独的动导数数值.为解决这个问题,利用滑移网格模拟强迫振荡运动,得到俯仰力矩系数对迎角变化率和俯仰角速度的动导数之和.利用旋转参考坐标系模拟定常拉升,得到俯仰力矩系数对俯仰角速度的动导数.利用旋转参考坐标系模拟匀速滚转,得到滚转力矩系数对滚转角速度的动导数.对有翼导弹和水上飞机进行了纵向和横向动导数的计算.计算结果与试验数据、文献数据以及其他方法得到的结果具有较好的一致性,表明提出的方法可用于复杂外形飞行器动导数计算.     

时域有限差分法连接边界电磁泄漏

用时域有限差分法计算目标的雷达散射截面时,一般用连接边界来引入平面入射波.理想情况下,当总场区没有散射目标时,该区域仅有入射波,散射场区电磁波为0.但在实际计算过程中,散射场区的电磁波一般不会严格等于0,这是因为在连接边界引入入射波时产生了电磁泄漏.一维情形下,用散射场区电场的平方和来衡量电磁泄漏程度.二维情形下,用等效原理将散射场区的电磁场进行远场外推,得到雷达散射截面,以此衡量电磁泄漏的大小.研究表明:时间步长、入射角度都能影响电磁泄漏大小.为使电磁泄漏较小,时间步长应接近于稳定性要求的最小步长,入射方向应避免垂直于计算区域边界.     

时间触发AFDX网络的设计和实时性分析

时间触发机制可以近一步提高航空电子全双工交换式以太网(AFDX,Avionics Full Duplex Switched Ethernet)的确定性,保障时间关键消息具有完全的时间确定性.将时间触发机制引入了AFDX网络,设计了时间触发ADFX网络(TTAFDX,Time-Triggered AFDX)的体系结构,包括协议栈、虚拟链路类型、端系统调度、交换机调度、透明通信机制和降级通信机制,并且设计了端系统和交换机的时刻调度算法.对TTAFDX网络从理论和仿真实验两方面进行了分析,验证了TTAFDX网络对时间关键消息的完全时间确定性的保障.