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Direct numerical simulation of energy separation effect in the near wake behind a circular cylinder

机译：圆柱后近尾流中能量分离效应的直接数值模拟

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Highlights•Energy separation in 2D compressible flow around a cylinder is studied numerically.•A comparative analysis of different energy separation mechanisms is performed.•The origin of the cooling of time-averaged flow in the wake is explained.•Local regions of reduced total enthalpy in the time-averaged flow are distinguished.•The reasons for the Eckert-Weise effect are clarified.AbstractBased on direct numerical simulation of two-dimensional Navier-Stokes equations, the effect of energy separation in unsteady vortex flows is investigated with the reference to the problem of a compressible viscous flow past a thermally insulated circular cylinder. The range of Reynolds (Re⩽103), Prandtl (0.1⩽Pr⩽10) and Mach (M⩽0.6) numbers considered corresponds mainly to the periodic vortex shedding regime. The energy separation, associated with the vortex shedding process, manifests itself in the appearance of cold and hot (in terms of total temperature) spots in the near wake. The main attention is focused on the comparative analysis of different mechanisms of total-enthalpy variation in a fluid particle moving around the cylinder, such as the action of viscosity, thermal conductivity, and unsteadiness of the flow. It is shown that the time-averaged total-enthalpy stratification in the boundary layer is caused by dissipative mechanisms. In the vortex formation region and in the vortex street, a decrease in the time-averaged total enthalpy is attributable mainly to the streamline oscillations. The known Eckert-Weise effect of low equilibrium temperature at the rearmost stagnation point of the cylinder is associated with the non-uniformities in the temperature and density fields, created by the evolution of recirculation zones near the body surface. For both instantaneous and time-averaged flow patterns, the regions of local increase and decrease in the total enthalpy are distinguished. It turned out that, in the time-averaged flow, the region responsible for the total-enthalpy decrease in the vortex formation zone does not affect the decrease in the total enthalpy in the developed vortex wake, and vice versa.
机译： 突出显示 • 围绕圆柱的二维可压缩流中的能量分离进行了数值研究。 • ，对不同的能量分离机制进行了比较分析。 • 在尾流中冷却时间平均流的起源。 • 在平均时间内总焓降低的本地区域 • 阐明了Eckert-Weise效应的原因。 摘要 < ce：abstract-sec id =“ as010” view =“ all”> 基于二维Navier-Stokes方程的直接数值模拟，考虑到流经隔热圆柱体的可压缩粘性流的问题，研究了非恒定涡流中的能量分离。雷诺数的范围（ Re ⩽ 10 3 ），Prandtl（ 0.1 ⩽ Pr ⩽ 10 ）和马赫数（ M ⩽所考虑的 0.6 ）数字主要对应于周期性涡旋脱落机制。与涡旋脱落过程相关的能量分离表现为在近尾时出现冷点和热点（就总温度而言）。主要注意力集中在对绕圆柱体运动的流体颗粒中总焓变的不同机制的比较分析，例如粘度，导热性和流动的不稳定性。结果表明，边界层时间平均总焓分层是由耗散机制引起的。在旋涡形成区域和旋涡街道中，时间平均总焓的降低主要归因于流线振荡。在圆柱体最后停滞点处较低的平衡温度，已知的Eckert-Weise效应与温度和密度场的不均匀性有关，该不均匀性是由于体表附近的回流区域的演变而产生的。对于瞬时流动模式和时间平均流动模式，总焓的局部增大和减小的区域都被区分出来。结果表明，在时间平均流中，导致涡旋形成区总焓降低的区域并不影响涡旋尾流中总焓的降低，反之亦然。

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