低耗散TVD格式及叶轮机内低马赫数流动模拟

推导了条件化预处理矩阵在守恒变量下的形式,以及三维任意曲线坐标系下的相应的系统特征值与特征矩阵。根据预处理技术修正了任意曲线坐标下的Harten-TVD格式,得到低耗散TVD格式,并讨论了抑制了压力速度失耦的方法。分别使用修正后低耗散格式与未修正的格式,对高负荷低压涡轮叶栅T106内低速流动:进口马赫数分别为0.1,0.01和0.001,进行数值模拟。计算表明,未修正格式不能得到有意义的结果,而修正后的低耗散格式,即使在极低的马赫数流动下,也工作良好。同时可以注意到:对于无粘流动,三种进口马赫数条件下,流场内等压线分布几乎是一致的。      

最少空测采样飞行起落次数设计准则

如何经济、科学地确定最少空测采样飞行起落次数,并能保证实测载荷参数数据的可比性与再现性,是目前国内外在编制飞机载荷谱时十分关注的问题。根据ｔ分布理论,按照一定置信度和误差要求,给出了确定飞机最少空测采样飞行起落次数的设计准则,以此作为现场实施空测采样的依据。     

雷诺数对涡轮部件性能的影响

利用数值模拟手段研究了雷诺数对低压涡轮部件性能的影响,分析了低压涡轮内部流动的变化。结果表明低压涡轮效率随雷诺数降低而下降,且其变化趋势为非线性变化;叶片表面速度分布亦发生较明显的变化,导致叶型损失与二次流损失增大;结果还表明叶片表面速度分布的设计对涡轮性能随雷诺数变化的规律具有重大影响,在低雷诺数条件下涡轮部件的设计中需加以注意。      

微型飞行器气动特性和飞行控制

微型飞行器的主要题实质是由于飞行器微小型化面临的低Re数流动引起的附加问题.本文结合微型飞行器的全系统关键技术攻关,分别讨论微型飞行器低Re数绕流特点和机理;不同外形的低Re数气动特性以及飞行控制技术中的相关科学问题.     

雷诺数变化对翼型边界层发展及失速特性的影响

翼型失速及其边界层发展是飞行器设计中的基础科学问题,而雷诺数变化对其影响很大。针对后缘失速翼型,采用Menter k-ω SST模型及耦合扰动放大因子输运方程的转捩模型,进行雷诺数变化对层流-湍流转捩边界层特性和失速特性的影响分析。结果表明:雷诺数增大时,对于转捩边界层,当地涡量雷诺数增大,转捩前移且分离泡减小,流动能量耗散减小,翼型整体表面剪切效应增强,动能更充沛,流动自持能力增强,压力分布可以维持较长距离的梯度抵抗分离能力增强;因此雷诺数增大使翼型失速迎角提高、升力系数增加。     

高旋转数下不同通道转角梯形带肋回转通道的换热特性

为研究截面形状和旋转效应对高压涡轮动叶内部冷却通道换热的影响，对雷诺数为10000～50000，旋转数为0~209，通道转角为0°、225°、45°的带直肋双流程梯形截面通道换热特性进行了实验研究。结果表明:静止状态下，在第一通道，梯形通道后缘换热强于前缘；在第二通道，前、后缘换热区别不大，后缘的换热略强于前缘。旋转状态下，对0°通道转角，随旋转数的增大，第一通道的后缘面换热仍强于前缘面和外侧面，且差异更明显；第二通道前缘换热相对后缘增强。在较高旋转数（旋转数大于1）时，0°通道转角工况的换热最强，45°转角最弱。      

低雷诺数下小型无人机翼型气动特性分析

以小型无人机翼型研究为背景,利用基于线性稳定性理论的eN方法对对小型无人机常用的翼型CLARKY在雷诺数Re=1.0×10~5、5×10~5、1.0×10~6,迎角由-5°~20°时的气动性能进行了计算和对比分析。随着雷诺数的增大,翼型上表面的转捩位置不断向前缘移动,气流分离则由完全分离逐渐转变为层流分离泡结构,使得翼型的最大升力系数和临界迎角增大,阻力减小,最大升阻比显著增大,有利迎角逐渐减小,翼型CLARKY的气动特性逐渐得到改善。     

An ECR-PCR rule for fusion of evidences defined on a non-exclusive framework of discernment

In the research of uncertain information processing, Dempster-Shafer Theory (DST) provides a framework for dealing with uncertain information, where evidence is defined on a Frame of Discernment (FOD) consisting of mutually exclusive elements. However, the requirement of exclusiveness on FOD sometimes is not satisfied, as shown in Dezert-Smarandache Theory(DSmT), a derivative of DST. In DSmT, the non-exclusiveness is expressed by propositions’ intersection and the fusion of evidence is realized through a Proportional Conflict Redistribution (PCR) rule. In order to handle non-exclusive FODs, a new framework called D Number Theory (DNT) has been proposed recently, which quantifies the non-exclusive degree between propositions different from DSmT. In previous studies, an Exclusive Conflict Redistribution (ECR) rule has been designed in DNT to implement the fusion of evidence defined on a non-exclusive FOD, but there are some deficiencies in the ECR rule. In this paper, a new rule called ECR-PCR rule is proposed by combining the ECR and PCR rules to better implement the fusion of evidence defined on a non-exclusive FOD. Within the proposed rule, the definition of conflict utilizes the idea of ECR’s exclusive conflict, and the disposal of conflict is following the idea of PCR’s proportional redistribution. Properties of the ECR-PCR rule are presented. The effectiveness of the proposed new rule is verified through numerical examples and applications, in comparison with other fusion methods.     

Predicting near-wall turbulence with minimal flow units in compressible turbulent channel flows

Mach number effects on the near-wall turbulence in the absence of outer motions remain unclear so far. The present study extends the Minimal Flow Units (MFUs), a widely applied method to investigate near-wall turbulence free from the impact of large-scale motions in the outer region in incompressible channel flows, to compressible wall-bounded turbulence. The compressible near-wall turbulence in MFU proves accurate in replicating near-wall statistics, independent of Mach number and statistically equivalent to the universal signals extracted from the full-sized channel. It is further utilized as universal signals in the predictive models of compressible near-wall turbulence, which is capable of accurately predicting variances and joint probability density functions of velocity and temperature fluctuations.     

Similarity phenomena of lean swirling flames at different bulk velocities with acoustic disturbances

In this study, flame responses to acoustic disturbances with different frequencies and amplitudes were experimentally investigated in a lean premixed swirl-stabilized combustor operating at different bulk velocities. The total heat release rate fluctuations and spatial CH* chemiluminescence distributions were captured using a photomultiplier tube and high-speed camera, respectively. The results indicate that the heat release rate exhibits a relatively drastic oscillation and high-order harmonics for low-frequency disturbances. When the bulk velocity and forcing frequency were doubled simultaneously, similar flame structures were observed in the CH* chemiluminescence distributions. As the bulk velocity increases, the gain of the Flame Describing Function (FDF) extends toward the higher frequencies, and the delay time of the flame response decreases. The similarity among FDFs at different bulk velocities was effectively captured by introducing a non-dimensional parameter, defined as the ratio of the flame response delay to the forcing time scale, to replace the dimensional forcing frequency. Furthermore, the availability of the newly defined non-dimensional parameter was verified for flames with different swirl numbers, as this played an important role in determining the flame structures and associated unsteady heat release rate.