Decomposition of the turbulent kinetic energy field into regions of compressive and extensive strain

作者：Gampert M^*; Schaefer P; Goebbert J H; Peters N

来源：Physica Scripta, 2013, T155: 014002.

DOI：10.1088/0031-8949/2013/T155/014002

Based on direct numerical simulations of homogeneous shear turbulence, homogeneous isotropic decaying turbulence and a turbulent channel flow, the scaling of the two-point velocity difference along gradient trajectories as well as between the extreme points of the instantaneous turbulent kinetic energy field k is studied. In the first step, we examine the linear proportional to s . a(infinity) scaling, where s denotes the separation arclength along a gradient trajectory and a(infinity) is the asymptotic value of the conditional mean strain rate of large dissipation elements. Then, we investigate the scaling of the velocity difference between scalar extreme points as well as the probability density function of the Euclidean distance P(l) between them, conditioned on compressive and extensive strain regions. We observe that while the overall velocity difference along gradient trajectories and between diffusively connected scalar extreme points exhibits linear scaling behaviour proportional to l, the conditional velocity differences of extensive and compressive regions are in contrast to the K41 theory proportional to l(2/3). The scaling exponent of the overall comes to one part from the purely extensive (compressive) (), while the second contribution is due to the difference in weighting the different regions, thus involving the conditioned pdfs P(l(+)) and P(l(-)). We find that the latter relation scales with l(1/3). The decomposition of into two contributions scaling with l(2/3) and l(1/3), respectively, hence yields an alternative explanation for the observed linear regime.

• 出版日期2013-7