PREDICTION OF SOLID FREE-SURFACE JUNCTURE BOUNDARY-LAYER AND WAKE OF A SURFACE-PIERCING FLAT-PLATE AT LOW FROUDE-NUMBER/

Results are reported of a RANS simulation investigation on the predict ion of turbulence driven secondary flows at the free-surface juncture of a surface-piercing flat plate at low Froude numbers. The turbulence model combines a nonlinear eddy viscosity model and a modified versio n of a free-surface correction formula. The different elements of the model are combined and the model constants calibrated based on the pre mises that the anisotropy of the normal stresses is mainly responsible for the dynamics of the flow in the juncture region, and an accurate modeling of the normal-stress anisotropy as obtained from the data is a primary requirement for the successful prediction of the overall flo w field. The predicted mean velocity streamwise vorticity, turbulent k inetic energy, and other quantities at the juncture are then compared with data and analyzed with regard to findings of related studies. In agreement with the experimental observations, the simulated flow at la rge depths was essentially two-dimensional and displayed all the major features of zero pressure gradient boundary layer and wake, including the anisotropy of normal stresses in the near-wall region. In the bou ndary-layer free-surface juncture region, the major features of intere st that were predicted include the generation of secondary flows and t he thickening of the boundary layer near the fi ee surface. In the wak e free-surface juncture region, even though secondary flows and a thic kening of the wake, width near the free surface, were predicted in acc ordance with the experimental observation, the overall comparison with the experiment was not as satisfactory as the boundary-layer juncture . This is partly due to the lack of a strong coherent flow structure i n the wake juncture and the presence of possible wave effects in the w ake in the experiments. An examination of the terms in the Reynolds-av eraged streamwise vorticity equation reconfirmed the importance of the anisotropy of the normal Reynolds stresses in the production of strea mwise vorticity. The free-surface wave elevations were negligible for the present model problem for the nonzero Froude number studied. Final ly concluding remarks are presented with regards to extensions for pra ctical geometries such as surface ship flows.