Study of fractal oscillating grid turbulence using Direct Numerical Simulation and Particle Image Velocimetry*

Oscillating grid flows have been classically studied by experimental methods [1] while fractal fixed grids turbulence has been analysed either by experimental [2] or numerical methods. Fractal oscillating grid flows were recently studied by an experimental PIV method and we propose here a complementary approach by direct numerical simulations of the turbulence generated by such a stirring system. A simple Cartesian and 3 fractal grids (fractal Cartesian, fractal square and fractal I-shaped) were considered experimentally and for the simulations. The DNS simulations were performed by using mesh morphing strategies to mimic the vertical sinusoidal movement of the grids. Both experimental data and data from numerical simulations in the statistically steady state were analysed thanks to the triple Reynolds decomposition [3].

[1] Yan J., Cheng N.-S., Tang H.-W., and Tan S. K., Journal of Hydraulic Research 45, 2007.

[2] Hurst D. and Vassilicos J. C., Physics of Fluids 19, 2007.

[3] Reynolds W. C. and Hussain A. K. M. F., Journal of Fluid Mechanics 54, 1972.