Lattice-Boltzmann Ship Airwake Simulation with Atmospheric Boundary Layer Inflow Using Synthetic Eddy Method

Accurate and quick-turnaround ship airwake simulations are essential for better understanding of shipboard helicopter aerodynamic interactions. However, for most realistically modeling a ship airwake, the interaction of the ship with the turbulent atmospheric boundary layer (ABL) must be resolved. In this study, an ABL was generated in the Lattice-Boltzmann simulation using the Synthetic Eddy Method (SEM), and the effects of the ABL inflow on the airwake of the Simple Frigate Shape 2 (SFS2) ship model were assessed. The Reynolds stress tensor components necessary for the SEM were obtained from particle image velocimetry (PIV) measurements. Mean velocity and turbulence intensity profiles obtained from experimental measurements and the Lattice-Boltzmann simulation were compared to profiles available in the literature. Results indicated that the profiles obtained from the PIV and simulations closely resembled the profiles in the literature. Ship airwake data from the LBM simulations were compared to the PIV data at several cross-planes on the ship, which showed good correlation. Frequency analysis revealed that a realistic ABL simulation that includes the effects of turbulence is necessary to accurately produce flow conditions in regions primarily affected by the inflow, but effects of the ABL become secondary near the ship. A new quantitative methodology to estimate pilot workload derived from the flow field was proposed to complement existing more qualitative workload ratings from flight test or piloted flight simulations. Analysis with this method estimated similar pilot workloads for steady and realistic (i.e., turbulent) ABL.