Numerical visualisation on applying a five-stage multi-scaled square turbulence-generating grid to generating turbulence

This study presents the numerical visualisation of turbulence generated by a five-stage square-type multi-scale turbulence grid. The present study applies a turbulence grid with an increased number of stages to five, in contrast to previous studies using multi-scale turbulence grids with four stages. For the present numerical visualisation, direct numerical analysis is used in this analysis. This analysis uses the high-order central difference schemes and the third-order Runge-Kutta scheme. In addition to the multi-scale turbulence grid with five stages, the present study also covers two turbulence grids with four stages for reference. By using the external force term in the governing equations, the present multi-scale turbulence grids were formed numerically in the computational domain. The spatial homogeneity of the downstream turbulence field is approached in this work. The turbulence generated by the turbulence grids with four stages is characterised by a flow structure with a doughnut-like instantaneous velocity figure in the downstream region. By examining contour diagrams of the streamwise instantaneous velocity, the present study can see that the spatial homogeneity of the turbulence field downstream is improved by increasing the number of stages for the turbulence grid.