  The paper presents a synthetic turbulence generator (STG) for the lattice
Boltzmann method (LBM) at the interface of the Reynolds averaged Naiver-Stokes
(RANS) equations and the LBM Large Eddy Simulation (LES). We first obtain the
RANS velocity field from a finite volume solver at the interface. Then, we
apply a numerical interpolation from the RANS velocity field to the LBM
velocity field due to the different grid types of RANS and LBM. The STG method
generates the velocity fluctuations, and the regularized LBM reconstructs the
particle distribution functions at the interface. We perform a turbulent
channel flow simulation at Re_{\tau} = 180 with the STG at the inlet and the
pressure-free boundary condition at the outlet. The velocity field is
quantitatively compared with the periodic lattice Boltzmann based LES (LES-LBM)
channel flow and the direct numerical simulation (DNS) channel flow. Both
adaptation length and time for the STG method are evaluated. Also, we compare
the STG-LBM channel flow results with the existing LBM synthetic eddies method
(SEM-LBM) results. Our numerical investigations show good agreement with the
DNS and periodic LES-LBM channel flow within a short adaptation length. The
adaptation time for the turbulent channel flow is quantitatively analyzed and
matches the DNS around 1.5 to 3 domain flow-through time. Finally, we check the
auto-correlation for the velocity components at different cross-sections of the
streamwise direction. The proposed STG-LBM is observed to be both fast and
robust. The findings show good potential for the hybrid RANS/LES-LBM based
solver on the aerodynamics simulations and a broad spectrum of engineering
applications.
