Lars Davidson

A novel wire mesh consisting of very fine wires and pores is numerically investigated for the purpose of noise reduction. To develop a numerical model for this wire mesh, a set of experimental flow-field data has been deployed for the model validation. The experimental data were measured with only 22% of the wind-tunnel cross section covered by the wire mesh, taking into account the vortex shedding from both sides of the wire-mesh fairing. It is found that existing wire-mesh models using a damping-type source term proportional to the square of flow velocity do not perform well in modeling this novel wire mesh. To tackle this issue, an improvement is proposed by additionally introducing a linear term to account for the permeability of the wire mesh, based on another set of experiments with the wind-tunnel cross section fully covered by the wire mesh. The proposed model is then validated against the experimental data, demonstrating its capability in modeling the wire mesh. Subsequently, the model is applied to a tandem cylinder configuration. Results show that a wide but short-span wire mesh significantly reduces the dominant tone of tandem cylinders, noise at higher frequencies, as well as the overall sound pressure levels.

The paper presents a synthetic turbulence generator (STG) for the lattice Boltzmann method (LBM) at the interface of the Reynolds averaged Navier–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 Reτ=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 the adaptation length and time for the STG method are evaluated. Also, we compare the STG-LBM channel flow results with the existing LBM synthetic eddy 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 1.5–3 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.