Area rule of velocity circulation in two-dimensional instability-driven turbulence beyond the inertial range (2504.21512v1)

Abstract: Since Kolmogorov's theory, scaling properties in the inertial range have been a key topic in turbulence research. However, the velocity statistics show non-universality in three- and two-dimensional turbulence. Migdal (1995) proved the velocity circulation area rule which states the probability density function (PDF) of circulation is only a function of the minimal surface area enclosed by the loop but not the shape of the loop, and later a bifractal universal behavior is found for circulation in three- and two-dimensional turbulence and quantum turbulence (Iyer et al. 2019; M\"uller et al. 2021; Zhu et al. 2023). This paper finds that the velocity circulation area rule can be generalized in two-dimensional instability-driven turbulence to all scales that are not limited to the inertial range. However, similar to the three-dimensional case, the variance of circulation is size-dependent, and compared with the circulation PDFs, the variance-normalized PDFs have a significantly weaker dependence on the shape of the loop. We also discussed the area rule for 8-loops and double loops. We found that the normalized PDF depends only on the scalar area of the 8-loop. However, the area rule for other complex loops, such as double loops, remains an open question.