BI-STABLE STATES IN THE WAKE OF A FINITE-WIDTH DOUBLE BACKWARD FACING STEP

Other conference contribution, 2019

The flow past a generic ship model is investigated numerically using well-resolved large eddy simulations
at Re = 8 × 10 4 . The geometric configuration at the rear of the model is analogous to a double backward
facing step, and it permits the occurrence of bi-stable flow states on each step; with an asymmetrical flow
topology being observed in each of the flow states across the longitudinal midplane. The mean flow topology
on the top step was observed to be anti-symmetrical to the flow topology on the bottom step, and the two
flow states are anti-symmetrical to each other. By introducing a base cavity on the top step, the asymmetrical
flow is suppressed on both the steps; leading to the elongation of the re-circulation bubble on each step, and
a reduction in the drag coefficient. The wake behind the model is analysed, and occurrence of asymmetrical
flow is attributed to the difference in the strength of the streamwise vortices along the lateral edges of the top
step.