We study a technique for verification of stress and pressure computations on boundaries in flow simulations. We utilize existing experiments to provide validation of the simulations. We show that this approach can reveal critical flaws in simulation algorithms. Using the successful computational algorithms, we examine Lamb's model for cylinder drag at low Reynolds numbers. We comment on a discrepancy observed in an experimental paper, suggesting that the domain size may be a contributing factor. Our simulations on suitably large domains confirm Lamb's model. We highlight a paradox related to imposing Dirichlet (Stokes) boundary conditions on polygonal approximations of the curved surface using finite-element methods that are exactly divergence free. The finite-element simulations provide very poor representations of drag when the boundary conditions are imposed strongly. We demonstrate that relaxing the boundary conditions using Nitsche's method restores high-order approximation.

翻译：本文研究了一种在流动模拟中验证边界应力与压力计算的技术。我们利用现有实验为模拟提供验证，并表明该方法能够揭示模拟算法中的关键缺陷。通过采用成功的计算算法，我们检验了低雷诺数下圆柱阻力的Lamb模型。针对某实验论文中观测到的偏差，我们提出计算域尺寸可能是影响因素之一。在适当大尺度域上的模拟结果证实了Lamb模型。我们揭示了在采用精确无散有限元方法处理弯曲表面多边形近似时施加Dirichlet（Stokes）边界条件所存在的悖论：当强施加边界条件时，有限元模拟对阻力的表征效果极差。通过采用Nitsche方法松弛边界条件，我们证明了高阶近似的恢复能力。