Air-flow distortion and wave interactions on research vessels: An experimental and numerical comparison

Reynolds-averaged Navier-Stokes (RANS) and large eddy simulation (LES) are two schemes for modeling turbulent flows. Here they are compared for modeling flow distortion over the oceanographic research vessel R/V Knorr, which is important for correcting observations from sonic anemometers. Using the OpenFOAM RANS solver SimpleFOAM and the LES solver PisoFOAM, computations are compared with experimental data taken from various anemometer sites on-board the research vessel. The LES showed mean accuracy levels of ∼3% of the wind speed bias whereas the RANS simulations showed mean accuracies of ∼7%. A LES analysis of the wind speed vector pitch and yaw was also conducted. The dominant forcing was found to be the pitch, which gave a 7% increase to overall magnitude of the wind vector. It was also found that the pitch of the wind speed was the main component responsible for the horizontal flow distortions, found to be due to flow separation in the 10-20  ms−1 range. We also use the LES simulations over a range of orientations from −60° to +60°, in increments of 10°. The numerical analysis showed close agreement to experimental measurements with a 6% mean difference prediction due to flow distortion effects. We also explore two different methods to define a wave induced flow distortion correction and when finally added to the air-flow distortion correction, improved the overall accuracy of the models by 3%.