Effects of curvature on rarefied gas flows between rotating concentric cylinders
Effects of curvature on rarefied gas flows between rotating concentric cylinders
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DOI：
10.1063/1.4807072
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发表时间：
2013-05
影响因子：
4.6
通讯作者：
N. Dongari;C. White;T. Scanlon;Yonghao Zhang;J. Reese
中科院分区：
文献类型：
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作者：
N. Dongari;C. White;T. Scanlon;Yonghao Zhang;J. Reese
为了研究曲面上努森层的非平衡效应，考虑了两个同心旋转圆柱之间的气体流动。我们使用一种新的幂律（PL）壁标度方法研究了近壁区的非线性流动物理。该PL模型通过考虑边界对分子自由程的限制效应，在近壁区引入了努森层效应。我们还报告了新的直接模拟Monte Carlo结果，涵盖了广泛的努森数和住宿系数，并为各种外，内圆筒半径比。将模拟结果与经典滑移流理论和PL模型进行了比较，发现非平衡效应不仅依赖于Knudsen数和调节系数，而且还受到表面曲率的显著影响.这两种理论模型的相对优点和局限性进行了探讨稀疏和曲率效应。PL模型能够捕捉到一些与克努森层相关的非线性趋势，直到早期过渡流态。本研究还阐明了经典的滑移流理论的局限性，即使在早期的滑移流政权的曲率较高的测试情况下，虽然该模型表现出良好的协议在整个滑移流政权的曲率较低的情况下。扭矩和速度剖面的比较还表明，对整体流动特性的良好预测并不一定能保证所用理论模型的准确性，重要的是要证明场变量也能得到令人满意的预测。
The gas flow between two concentric rotating cylinders is considered in order to investigate non-equilibrium effects associated with the Knudsen layers over curved surfaces. We investigate the nonlinear flow physics in the near-wall regions using a new power-law (PL) wall-scaling approach. This PL model incorporates Knudsen layer effects in near-wall regions by taking into account the boundary limiting effects on the molecular free paths. We also report new direct simulation Monte Carlo results covering a wide range of Knudsen numbers and accommodation coefficients, and for various outer-to-inner cylinder radius ratios. Our simulation data are compared with both the classical slip flow theory and the PL model, and we find that non-equilibrium effects are not only dependent on Knudsen number and accommodation coefficient but are also significantly affected by the surface curvature. The relative merits and limitations of both theoretical models are explored with respect to rarefaction and curvature effects. The PL model is able to capture some of the nonlinear trends associated with Knudsen layers up to the early transition flow regime. The present study also illuminates the limitations of classical slip flow theory even in the early slip flow regime for higher curvature test cases, although the model does exhibit good agreement throughout the slip flow regime for lower curvature cases. Torque and velocity profile comparisons also convey that a good prediction of integral flow properties does not necessarily guarantee the accuracy of the theoretical model used, and it is important to demonstrate that field variables are also predicted satisfactorily.