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Tip vortex cavitation (TVC) affects hydrodynamic performance and can cause drastic vibration and noise; therefore, it is crucial to predict the evolution of TVC, understand its generation mechanism, and determine methods to control it. In this work, a large eddy simulation (LES) was performed to resolve unsteady turbulence, and the Schnerr-Sauer cavitation model was used to capture transient cavitating flow. Both wetted and cavitating conditions were used in the first step to validate the numerical methods. The mechanism of TVC development and the interactions between the tip vortex and TVC were also revealed. Next, active control by water injection was performed to suppress TVC, and the side and top injection circumstances were explored and compared. Parametric studies were conducted for the side injection condition by changing the injection velocity and angle. The results showed that both side and top injections had remarkable effects on TVC control. Flow field analysis demonstrated that the top injection flow affected the local velocity magnitude and direction of the incident flow of the tip vortex, thus reducing the vortex strength and TVC. For the side injection condition, the injection flow directly influenced the incepted structures of the tip vortex. As a result, injection flow deeply deformed the tip vortex and decreased the generation and intensity of TVC. Furthermore, increasing the injection velocity or the component of the velocity in the cross-streamwise direction could effectively increase the cavitation inhibition rate.

To estimate the maneuverability of a submarine at the early design stage, an accurate evaluation of the hydrodynamic coefficients is important. In a collaborative exercise, the authors performed calculations on the bare hull DRAPA SUBOFF submarine to investigate the capability of viscous-flow solvers to predict the forces and moments as well as flow field around the body. A typical simulation program was performed for both the steady drift tests and rotating arm tests. The same grid topology based on multi-block mesh strategy was used to discretize the computational domain. A procedure designated drift sweep was implemented to automatically increment the drift angle during the simulation of steady drift tests. The rotating coordinate system was adopted to perform the simulation of rotating arm tests. The Coriolis force and centrifugal force due to the computation in a rotating frame of reference were treated explicitly and added to momentum equations as source terms. Lastly, the computed forces and moment as a function of angles of drift in both conditions are compared with experimental results and literature values. They always show the correct trend. Flow field quantities including pressure coefficients and vorticity and axial velocity contours are also visualized to vividly describe the evolution of flow motions along the hull.

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