明渠湍流边界层中颗粒的运动与分布

利用直接数值模拟、点球浸入边界法和颗粒离散元法相结合的方法, 模拟了颗粒在明渠湍流边界层中的运动, 并对颗粒的瞬时位置进行了Voronoi 分析, 定量研究了颗粒在湍流边界层中的运动和分布规律. 研究发现:颗粒的输运对湍流的统计特征有影响, 其运动与近壁区湍流拟序结构密切相关, 在"喷发"结构作用下被带离壁面, 在"扫掠" 结构和自身重力作用下回到壁面; 在湍流边界层中, 颗粒倾向于聚集在低流速带, 呈条带状分布;颗粒在大部分时间处于"簇"状态, 偶尔跳跃到"空" 状态, 但能够很快回到邻近低速区域.      

热激励器对超声速圆管射流的控制机理

采用大涡模拟方法研究了热激励器对马赫1.3 超声速圆管射流涡结构的影响, 采用加入净热源的方法模拟了热激励器的热效应, 分析了不同激励模态(m =±1 和m =±4) 的降噪和增加射流掺混的效果. 研究发现: (1)射流在受到激励作用时, 产生了更大的径向和周向速度扰动, 这有利于流向涡的形成, m =±1 激励模态下流向涡的发展更快, 特别是在摆动面上会有更大的增长速度; (2) 气动噪声分布的频带很宽, 激励作用对抑制高频气动噪声有较强的作用; (3) 对于在喷管壁面处产生的固壁噪声, m =±4 模态下的激励作用一定程度上加强了固壁噪声.      

合成射流对失速状态下翼型大分离流动控制的试验研究

为研究低速状态合成射流在抑制翼型气流分离和推迟失速方面的控制机理, 开展了NACA0021 翼型失速特性射流控制的风洞试验研究. 通过系统性的模型测力、翼型瞬态流场粒子图像测速和边界层速度测定的对比试验, 深入探索了合成射流各参数对翼型失速特性控制效果的影响规律. 试验结果表明射流偏角在翼型升力和失速迎角控制方面的效果对射流动量系数较为敏感: 当动量系数较大时, 近切向射流的控制效果更好. 射流动量系数为0.033 时, 偏角30°的射流使得翼型升力系数峰值提高23.56%, 失速迎角增大5°; 而动量系数较小时, 偏角较大的射流能够获得最佳控制效果. 射流动量系数为0.0026 时, 法向射流对翼型最大升力系数控制效果最好(提高9.2%).      

Flow and heat transfer characteristics over rectangular blocked surfaces

Heat transfer and flow measurements were recorded over blocked surfaces to investigate the effects of flow velocity and block shape on flow separation and heat transfer. The results indicated that the flow separation occurred particularly on the first block and after the last blocks. The flow separation and block thickness resulted in higher turbulence and heat transfer, particularly in laminar flow. The average Stanton number increased as high as 125% in laminar, 80% in transitional, and 50% in turbulent flows above those of flat plate values. A new empirical equation indicated a good agreement with the experimental and numerical results.     

Effect of impingement jet on the full-coverage film cooling system with double layered wall

The present study was conducted to evaluate the total cooling effectiveness in combined full-coverage film cooling and impingement jet using an infrared thermographic technique. The effect of film cooling hole angle, blowing ratio, and height to diameter ratio between the film cooling and impingement jet plates was discussed. The total cooling effectiveness increased as impingement jet cooling was added. The angled film cooling holes had approximately 4.6% higher total cooling effectiveness than the normal film cooling holes. The total cooling effectiveness was almost constant regardless of height to diameter ratio, but enhanced as the blowing ratio was increased.     

Quantum polarization fluctuations of partially coherent dark hollow beams in non-Kolmogorov turbulence atmosphere

Non-classical polarization properties of dark hollow beams propagating through non-Kolmogorov turbulence are studied. The analytic equation for the polarization degree of the quantization partially coherent dark hollow beams is obtained.It is found that the polarization fluctuations of the quantization partially coherent dark hollow beams are dependent on the turbulence factors and beam parameters with the detection photon numbers. Furthermore, an investigation of the changes in the on-axis propagation point and off-axis propagation point shows that the polarization degree of the quantization partially coherent dark hollow beams presents oscillation for a short propagation distance and gradually returns to zero for a sufficiently long distance.     

逆压梯度边界层未分离情况下的湍流模式适用性研究Turbulence model applicability for boundary layer flow with adverse pressure gradient in attached case

边界层逆压梯度作用下的流动是许多工程中的一个基础问题,由于逆压梯度作用,流动形态复杂,使得数值模拟有很大的难度。基于雷诺平均纳维‐斯托克斯RANS（Reynolds Averaged Navier‐Stokes）方程对二维平板逆压梯度边界层作数值计算研究,选取6种代表性的湍流模式,得到局部摩擦系数的数值解,与实验值比较,发现k‐ω模式具有很好的精度。基于该湍流模式,给出了湍动能分布,该结果有助于认识逆压梯度边界层流动的复杂特征。     

Assessment of a high-order accurate Discontinuous Galerkin method for turbomachinery flows

In this work the capabilities of a high-order Discontinuous Galerkin (DG) method applied to the computation of turbomachinery flows are investigated. The Reynolds averaged Navier–Stokes equations coupled with the two equations k-ω turbulence model are solved to predict the flow features, either in a fixed or rotating reference frame, to simulate the fluid flow around bodies that operate under an imposed steady rotation. To ensure, by design, the positivity of all thermodynamic variables at a discrete level, a set of primitive variables based on pressure and temperature logarithms is used. The flow fields through the MTU T106A low-pressure turbine cascade and the NASA Rotor 37 axial compressor have been computed up to fourth-order of accuracy and compared to the experimental and numerical data available in the literature.     

大气压氩气射流等离子体的光谱特性研究

等离子体喷枪是一种重要的等离子体源,已成为近几年低温等离子体研究的一个重要课题。本文利用钨针-钨丝网电极制作了直流喷枪装置,在大气压空气中产生了稳定的等离子体羽,并采用发射光谱的方法,对等离子体羽的等离子体参数进行了研究。在钨针电极与钨丝网电极之间放出耀眼的白光,钨丝网电极出口的气流下游有火苗形状的等离子体羽喷出。在电压保持不变的条件下(13.5 kV),等离子体羽长度随气体流量增加而增大;在气体流量保持不变的条件下(10 L·min-1),羽长度随外加电压的增大而增大。在气体流量一定的条件下,放电电压和放电电流呈反比例关系,即电压随着电流的增大而减小,说明放电属于辉光放电。采集了该喷枪在300～800 nm范围内的放电发射光谱,通过玻尔兹曼方法对放电等离子体电子激发温度进行了测量。结果表明,电子的激发温度随外加电压的增大而降低,随着工作气体流量的减小而升高。利用放电的基本理论对上述现象做了解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。