大比例主梁节段模型涡激振动风洞试验分析

节段模型风洞试验是预估大跨度桥梁主梁涡激振动响应的有效途径之一。大比例主梁节段模型（通常为1：15～1：20）几何尺度更大,试验雷诺数更接近实桥值,同时在模型加工制作方面也可更精确地模拟主梁细节。通过一扁平钢箱梁1：20大比例节段模型试验,优化了检查车轨道位置,分析了涡激振动典型现象如振幅、涡振区与阻尼、Scruton数关系,迎角与斯托劳哈数5￡关系,双竖向涡振区等,为节段模型涡振试验结果向实桥拓展提供理论与试验基础。     

MHD控制激波诱导湍流边界层分离的机理分析

为了研究磁流体动力学(Magnetohydrodynamics:MHD)加速边界层对激波-湍流边界层相互作用的影响,用高阶有限差分法求解了小磁雷诺数近似的MHD湍流方程。其中,无粘通量采用WENN格式离散、粘性通量采用Roe平均中心差分离散,时间采用半隐式推进,并采取追赶法求解。计算给出了湍流、电场、磁场和电导率等参数对边界层分离的影响,数值结果显示:在同样的逆压梯度下,湍流边界层分离能更快地趋于稳态流场,且分离区比层流小;通过施加洛仑兹力加速,边界层速度型面变得更加饱满、位移厚度减小、分离点和再附点向激波与固壁的交点靠近,分离区尺寸减小甚至最终被消除。     

低雷诺数翼型局部振动非定常气动特性

针对低雷诺数翼型特殊的气动特性,采用基于动网格的非定常数值模拟方法,研究翼型表面不同弦向位置的局部蒙皮以不同频率及振幅振动时对低雷诺数翼型气动特性及流场结构的影响,揭示蒙皮振动增升减阻的机理。研究表明,在低雷诺数条件下局部蒙皮振动可有效提高翼型气动特性,与刚性翼型相比蒙皮局部振动可使翼型升力系数提高,阻力系数降低,升阻比提高。振动位置对翼型气动特性及流场结构有显著的影响,振动表面位于翼型前缘附近或位于层流分离泡中心时可有效控制翼型层流分离,从而提高翼型气动特性。振动频率对翼型表面层流分离及转捩位置均有显著的影响,随着振动频率增加,翼型气动特性出现最优值。与刚性翼型相比,表面振动使翼型转捩位置略向上游移动,摩擦阻力增加,但振动使等效翼型相对厚度减小,压差阻力明显减小。在小幅振动范围内,随着振幅增加,流场非定常特性更加显著,翼型升阻比增加。     

上游弯头对内锥流量计性能影响的仿真与实验研究

研究旨在获取上游弯头安装条件下内锥流量计的性能和所需要的直管段长度。研制了100mm口径、β值分别为0．45、0．65、0．85三种结构类型的样机。开展了上游单弯头、同一平面上连续两个90。成s型结构双弯头及互成垂直平面上连续两个90°双弯头的仿真和实验研究,仿真和实验的介质均为常温水,雷诺数范围分别为0．498×10^5～4．98×10^5和0．14×10。～4．5×10^5。仿真结果与实验结论一致,并利用平均流出系数相对误差及附加不确定度作为安装条件影响的主要评价标准,给出了上游弯头安装条件内锥流量计所需的直管段长度。     

飞机舱温数据处理方法的考核研究

通过编写飞机舱温数据处理与分析软件平台,对有关文献的舱温实测数据处理方法进行考核研究,结果表明：要使得到的样条逼近函数的误差最小,应合理选取自变量取值范围的分段数和样条次数。如若不然,在样条次数相同的情况下,分段计算得到样条逼近函数的误差可能要比在整个区间上不分段时得到的误差大。     

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...     

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.