Study of unsteady separated fluid flows using a multi-block lattice Boltzmann method

Abstract

Purpose Numerical simulations are performed for studying the vorticity dynamics of a dipole colliding with the wall in a bounded flow and the wake structure and separated flow properties past a circular cylinder at the values of Reynolds numbers. Design/methodology/approach The near wake statistics of separated fluid flows are investigated by using the lattice Boltzmann method (LBM) in a two-dimensional framework. A multi-block technique is applied to accurately resolve the flow characteristics by the grid refinement near the wall and preserve the stability of the numerical solution at relatively high Reynolds numbers. Findings The results show that the rolling-up of the boundary layer occurs due to the shear-layer instabilities near the surface which causes a boundary layer detachment from the wall and consequently leads to the formation of small-scale vortices. These shear-layer vortices shed at higher frequencies than the large-scale Strouhal vortices which result in small-scale high-frequency fluctuations in the velocity field in the very near wake. The present study also demonstrates that the efficiency of the multi-block LBM used for predicting the statistical features of flow problems is comparable with the solvers based on the Navier-Stokes equations. Practical implications Studying the separated flow characteristics in aerospace applications. Originality/value Applying a multi-block lattice Boltzmann method (LBM) for simulation of separated fluid flows at high-Reynolds numbers. Studying of the near wake statistics of unsteady separated fluid flows using the multi-block LBM. Comparison of flow characteristics obtained based on the LBM with those of reported based on the Navier-Stokes equations.