基于格子Boltzmann方法的平板射流大涡模拟

应用多GPU技术,将格子Boltzmann方法与大涡模拟相结合(LBM-LES),使用1.12×10⁸网格,对雷诺数Re=4 000,倾斜角α=30°,吹风比M=0.5工况下的平板单孔射流进行了大规模高性能数值模拟研究.合理的定性与定量结果验证了LBM-LES模拟平板射流的有效性与可行性.使用上亿的计算网格捕捉了精细的湍流拟序结构,有利于主流与射流之间的掺混机理研究.此外,使用6个K20M GPU并行计算,模拟了71 680 LBM时间步长,仅耗时15 402秒,计算性能达到521.24MLUPS,即每秒更新5.212 4×10⁸个网格点的数据.     

Flow and Heat Transfer Characteristics of in-Line Impinging Jets With Cross-Flow At Short Jet-To-Plate Distance

The aim of this research is to numerically and experimentally study the flow and heat transfer characteristics of in-line impinging jets in cross-flow. The jets from a row of round orifices are perpendicularly impinged on the inner surface of a rectangular wind tunnel at a short distance between the orifice plate and impinged surface (H) of 2D, where D is a diameter of the orifice. The jet velocity was fixed corresponding to Re = 13,400 for all experiments, and the cross-flow velocity was varied at three different velocity ratios (velocity ratio, jet velocity/cross-flow velocity) of 3, 5, and 7. The heat transfer characteristic was visualized using a thermochromic liquid crystal sheet, and the Nusselt number distribution was evaluated by an image processing technique. The flow pattern on the impinged surface was also visualized by an oil film technique. The numerical simulation was used to explore a flow interaction between the impinging jets and cross-flow. The results indicated that Nusselt number peak increased by the increasing cross-flow velocity for short jet-to-plate distance. For the range determined, the maximum local Nusselt number peak was obtained at VR = 3 as the consequence of high velocity and high turbulence kinetic energy of jet impingement.     

The Efficiency Analysis of a Finned Cross-flow Heat Recovery Unit

A finned convergent-divergent plate-type cross-flow heat recovery unit is manufactured and tested for efficiency analysis. Temperature and pressure drop experiments are conducted with various working conditions of the boiler, fan, preheater, and reheater of the system. Variation of Nusselt number and friction factor with Reynolds number is analyzed. Variation of effectiveness and exergy loss with number of transfer units is calculated and discussed in terms of extant literature. Experimental results indicate that the most important parameter affecting the heat transfer is winglet geometry and fluid velocity. The efficiency can be improved successfully by controlling these parameters for thermal applications.     

前缘曲率对三维边界层内被激发出非定常横流模态的影响研究

三维边界层感受性问题是三维边界层层流向湍流转捩的初始阶段,是实现三维边界层转捩预测与控制的关键环节.在高湍流度的环境下,非定常横流模态的失稳是导致三维边界层流动转捩的主要原因;但是,前缘曲率对三维边界层感受性机制作用的研究也是十分重要的课题之一.因此,本文采用直接数值模拟方法研究在自由来流湍流作用下具有不同椭圆形前缘三维（后掠翼平板）边界层内被激发出非定常横流模态的感受性机制;揭示不同椭圆形前缘曲率对三维边界层内被激发出非定常横流模态的扰动波波包传播速度、传播方向、分布规律、感受性系数以及分别提取获得一组扰动波的幅值、色散关系和增长率等关键因素的影响;建立在不同椭圆形前缘曲率情况下,三维边界层内被激发出非定常横流模态的感受性问题与自由来流湍流的强度和运动方向变化之间的内在联系;详细分析了不同强度各向异性的自由来流湍流在激发三维边界层感受性机制的物理过程中起着何种作用等.通过上述研究将有益于拓展和完善流动稳定性理论,为三维边界层内层流向湍流转捩的预测与控制提供依据.     

斜蜗舌对贯流风机内流的影响及降噪机制研究

本文提出采用一种新型的不等距蜗舌(这里统称为斜蜗舌)在提高风机的外特性性能的同时,相对降低噪声.通过试验与数值模拟,比较直叶片式,斜叶片式贯流风机分别用直蜗舌和斜蜗舌时内流、外特性及噪声频谱.采用三维Navier-Stokes方程和κ-ε两方程湍流模型对内部流场进行数值分析,发现与采用常规蜗舌的贯流风机不同的是斜蜗舌贯流风机偏心涡位置随着蜗舌间隙的变化而发生改变.本文旨在探讨斜蜗舌对贯流风机内流的影响及降噪的机制.