Abstract
Analysis of the energy transfer in scale space, in addition to the energy transport in physical space, is useful for obtaining a better understanding of inhomogeneous turbulence. In this work, the energy transfer in scale space is examined using the direct numerical simulation data of turbulent channel flow. A direct cascade of the streamwise and wall-normal components of the turbulent energy is seen, whereas an inverse cascade of the spanwise component is observed near the wall. The inverse energy cascade implies that the production term of the subgrid-scale (SGS) energy is negative in the averaged sense. The conditional average of the velocity field associated with the negative production is evaluated to extract typical flow structures contributing to the inverse cascade. As a result, a long streamwise vortex around the reference point, as well as a short one in the upstream region, is observed, which is reminiscent of a series of slightly tilted streamwise vortices with alternate signs of vorticity near the wall. The isosurface of the negative production attached to the long vortex suggests that the grid-scale velocity of the long vortex is enhanced by the SGS motion under the influence of the short upstream vortex. The enstrophy equation is further examined to confirm that the SGS effect increases the rotation of the long vortex.
5 More- Received 17 June 2019
DOI:https://doi.org/10.1103/PhysRevFluids.4.114609
©2019 American Physical Society