可压缩混合层中的大尺度结构及其作用初探

利用粒子示踪图像流动显示技术和粒子图像测速技术(PIV技术)研究了对流马赫数Mc=0.38时可压缩混合层发展早期出现的大尺度结构的形状和特性,并将这些混合现象与湍流脉动场结合起来研究了这些大尺度结构对流动混合效率的作用.将粒子示踪图像和湍流脉动强度场对比以后发现:混合层流动中早期出现的大尺度结构沿着顺时针方向旋转着向前移动;该结构上的流体微元具有高涡量.由于该结构旋转和高涡量产生了较大的诱导速度,加上该结构的非定常性导致在这些大尺度结构频繁出现的区域具有很高的脉动强度,从而可能带来较高的混合效率.     

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。     

一种锯齿状唇口超声速轴对称进气道特性

为探究锯齿状唇口对进气道气动特性的影响,完成了一种常规唇口轴对称进气道设计后,在保持其他基本构型参数和几何特征不变的基础上,通过对其唇口进行剪切构造出锯齿状切口,得到了一种锯齿状唇口超声速轴对称进气道,采用标准k-ε湍流模型对比分析了该进气道与原始型面进气道的气动特性.结果表明:锯齿状唇口进气道通过唇口溢流牺牲流量系数...     

旋转带肋直通道湍流流动TR-PIV实验

采用高频粒子图像测速系统(TR-PIV)测量了旋转带肋通道内的主流平均速度、雷诺切应力、再附点等参数,并研究其沿程变化规律,通道高宽比为1,肋的阻塞比为0.1,雷诺数为10000,旋转数从0变化到0.52,实验结果表明:静止时流动呈对称分布,但旋转后产生的哥氏力会极大地影响通道内的湍流流动,随着转速的增加,主流速度型偏...     

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.     

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.     

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.     

双层壁冷却结构中多排射流冲击冷却的换热和流阻特性

采用稳态热敏液晶技术对双层壁冷却结构中的多排(包括顺排和叉排)射流冲击冷却结构进行了风洞实验,同时结合数值模拟的方法,对两种射流冲击冷却结构的传热和流阻特性的差异进行了研究.实验结果表明:流量系数和冲击靶板上的努塞尔数均随着雷诺数的增大而增大,而冲击孔的排布方式对面平均努塞尔数的影响较小,但是叉排结构的流量系数高于顺排...     

镁粉与二氧化碳动态点火燃烧特性数值研究

Mg粉/CO₂粉末发动机是火星探测中较为理想的原位资源利用方案，为了掌握Mg/CO₂粉末发动机稳定点火燃烧特性，在考虑氧化层厚度对Mg颗粒熄火影响的基础上，基于涡耗散/有限速率模型建立了点火燃烧模型，并应用数值计算方法研究了Mg粉颗粒粒径（5μm， 10μm， 15μm， 20μm和25μm）、入口预混气流雷诺数（1500， 2000， 2500， 3000和3500）和CO₂/Mg氧燃比（0.5， 1， 1.5， 2和2.5）对Mg粉/CO₂动态点火燃烧的影响。计算结果表明：雷诺数和氧燃比恒定时，随着粒径从5μm增加到10μm，平均温度升高，平均点火时间延长，燃烧效率增加；随着粒径从10μm增加到25μm，平均温度降低，平均点火时间延长，燃烧效率减少。粒径和氧燃比恒定时，平均温度随雷诺数增加而下降；平均点火时间和燃烧效率随雷诺数增加基本不变。粒径和雷诺数恒定，随着氧燃比从0.5增大到1.5，平均温度升高；随着氧燃比从1.5增大到2.5，平均温度下降；平均点火时间和燃烧效率随氧燃比增大基本不变。     

A numerical study of segmented cooling-stream injection in supersonic film cooling

The present study proposes a segmented cooling-stream injection structure based on a certain coolant mass flow rate, and numerically investigates the effect of segmented cooling-stream injection on supersonic film cooling. The results indicate that without shock-wave impingement and with helium as the coolant, segmented cooling-stream injection can reduce the mixing between the mainstream and the cooling stream to produce better cooling performance than single injection, especially at larger coo...