Influenced by the fact that vorticity represents rotation for rigid body, people believe this idea also works for fluid flow. However, the vortex predictions by vorticity do not match experimental results, which drove scientists to look for more appropriate methods to identify vortex. All vortex identification methods can be categorized into three generations. The vorticity-based method is classified as the first generation. Methods relying on eigenvalues of velocity gradient tensor are considered as the second generation. People still believe vorticity is vortex since vorticity theory looks correct in mathematics, but all other methods are only scalars and unable to indicate the swirl direction. Recently, a new vortex identification method called Liutex is innovated. It is regarded as the third-generation method, not only overcoming all previous methods’ drawbacks but also having a clear physical meaning. The direction of Liutex represents the swirl axis of rotation, and its strength is equal to twice the angular speed. In this paper, we did a correlation analysis between vorticity, Q, λ_ci, λ₂ methods and Liutex based on a direct numerical simulation (DNS) case of boundary layer transition. The results show that the correlation between vorticity and Liutex is very small or even negative in strong shear regions, which demonstrates that using vorticity to detect vortex lacks scientific foundation and vorticity is not appropriate to represent vortex. The correlation analysis also shows that the second generation is contaminated too by shear and thus is not accurate to identify the vortex structure.

受涡度代表刚体旋转的事实的影响，人们认为这种想法也适用于流体流动。但是，通过涡度进行的涡旋预测与实验结果不符，这驱使科学家们寻找更合适的方法来识别涡旋。所有涡旋识别方法可分为三代。基于涡度的方法被归类为第一代。依赖速度梯度张量特征值的方法被认为是第二代方法。人们仍然认为旋涡是旋涡，因为旋涡理论在数学上看起来是正确的，但是所有其他方法只是标量，无法指示旋涡的方向。最近，创新了一种称为Liutex的涡流识别新方法。它被认为是第三代方法，不仅克服了以前所有方法的缺点，而且具有明确的物理意义。Liutex的方向表示旋流的旋转轴，其强度等于角速度的两倍。在本文中，我们对涡度，Q，λ _CI，λ _2点的方法和Liutex基于直接数值模拟边界层过渡的（DNS）的情况。结果表明，在强切变区，涡度与Liutex的相关性很小，甚至为负，说明利用涡度检测涡旋缺乏科学依据，涡度不适合代表涡旋。相关分析还表明，第二代也被剪切污染，因此无法准确识别涡旋结构。