Large eddy simulation and experimental studies of a confined turbulent swirling flow
Large eddy simulation and experimental studies of a confined turbulent swirling flow
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DOI：
10.1063/1.1769420
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发表时间：
2004-07
影响因子：
4.6
通讯作者：
Ping Wang;X. Bai;M. Wessman;J. Klingmann
中科院分区：
文献类型：
--
作者：
Ping Wang;X. Bai;M. Wessman;J. Klingmann
采用激光多普勒测速（LDV）和大涡模拟（LES）研究了模型自卸燃烧室内的受限等温湍流旋流。目的是更深入地了解自卸燃烧室的流动和湍流结构，并检验LES预测湍流旋流的能力。在LDV测量中采用了折射率匹配技术来改善近壁数据。采用了一种具有尺度相似子滤波尺度模型的笛卡尔网格高阶有限差分格式。在LES中测试了不同能谱的湍流流入边界条件、不同的流出边界条件和网格分辨率。对三种不同旋流数和雷诺数的试验情况进行了测量和仿真研究。雷诺数在10000 ~ 20000之间，旋流数在0 ~ 0.43之间。在适当的流入、流出边界条件和精细的网格分辨率下，LES结果与LDV数据吻合较好。实验和数值结果表明，在燃烧室突然膨胀后和靠近燃烧室轴线的内循环区内，湍流具有高度的各向异性。湍流沿下游方向衰减迅速，湍流结构高度依赖于进口旋流的水平。低旋流数时，湍流主要产生于突胀后的剪切层；在高旋流数时，近轴流动变得非常不稳定，发生涡流击穿。涡流击穿引起的燃烧室轴附近的剪切层产生了大部分的湍流动能。在近轴涡旋击穿区发现了大尺度运动（相干结构）。导管中的螺旋流在突然膨胀附近破裂，形成一个大的气泡状再循环区，其中心绕轴缓慢移动。在气泡的下游，旋转大尺度方位流运动的核心远离燃烧室轴，并以18-25 Hz的频率（斯特劳哈尔数约为0.17-0.4）绕轴旋转。随着旋流数的增加，相干结构更加明显，内部再循环区向上游移动。在所有考虑的涡流数下，LES成功地模拟了涡击穿、内部再循环区和各向异性湍流结构。(C) 2004年美国物理研究所。
Laser Doppler velocimetry (LDV) measurement and large eddy simulation (LES) were used to study confined isothermal turbulent swirling flows in a model dump combustor. The aim was to gain deeper understanding of the flow and turbulence structures in dump combustors and to examine the capability of LES for prediction of turbulent swirling flows. A refractive index matching technique is used in the LDV measurement to improve the near-wall data. A high-order finite difference scheme on Cartesian grids with a scale-similarity subfilter scale model is used in the LES. Turbulent inflow boundary conditions with different energy spectra, different outflow boundary conditions, and grid resolutions are tested in the LES. Three test cases with different swirl numbers and Reynolds numbers are studied in the measurements and the simulations. The Reynolds numbers range from 10 000 to 20 000, and the swirl number is varied from 0 to 0.43. With appropriate inflow, outflow boundary conditions, and fine grid resolution, the LES results are in fairly good agreement with the LDV data. The experimental and numerical results show that turbulence in the dump combustor is highly anisotropic behind the sudden expansion and in the internal recirculation zone near the axis of the combustor. Turbulence decays rapidly along the streamwise direction downstream, and the structure of turbulence depends highly on the level of inlet swirl. At low swirl numbers, turbulence is primarily generated in the shear layer behind the sudden expansion; at high swirl numbers the near axis flow becomes very unstable and vortex breakdown occurs. The shear layer near the axis of the combustor caused by vortex breakdown generates most of the turbulent kinetic energy. Large-scale motions (coherent structures) are found in the near axis vortex breakdown region. A helical flow in the guiding pipe breaks down near the sudden expansion to form a large bubble-like recirculation zone whose center moves slowly around the axis. Downstream of the bubble the core of the rotational large scale azimuthal flow motion is off the combustor axis and rotates around the axis at a frequency about 18-25 Hz (Strouhal number about 0.17-0.4). As the swirl number increases the coherent structure becomes more evident, and the internal recirculation zone moves upstream. LES successfully simulated the vortex breakdown, the internal recirculation zones and the anisotropic turbulence structures for all the swirl numbers considered. (C) 2004 American Institute of Physics.