Vortex tuning of a submarine by Liutex force field model

Vortical structures of a submarine with appendages are fully turbulent and complex.Thus,flow control and vortex manipulation are of great importance for the hydrodynamic performance and acoustic characteristics.Take the generic submarine model DARPA Suboff as the test case,a vortex tuning method based on the Liutex force field is proposed to manipulate the vorticity field.Viscous flow past the submarine model in straight-line motion at a Reynolds number of 1.2×107 is achieved by solving the Reynolds averaged Navier-Stokes(RANS)equations.Multi-block structured mesh topology is used to discretize the computational domain,and the shear stress transport(SST)k-ωturbulence model is implemented to close the equations.The control of vortex is achieved by introducing additional source terms based on Liutex vortex definition and identification system to the RANS equations.The resistance acting on the submarine,flow field as well as the vortical structures are compared and analyzed.Results show that Liutex force model can effectively reduce the resistance by 9.31%and change the vortical structures apparently.

Numerical Simulation and Experimental Study of the Effects of Disposal Space on the Flow Field Around the Combined Three-Tube Reefs

The artificial reefs placed on the seabed with different layouts and disposal spaces will produce variational flow field. The intensity and scale of the combined three-tube artificial reefs with different layouts at five Reynolds numbers（Re） are numerically investigated by use of the RNG k-ε turbulent model and SIMPLEC algorithm. A stationary no-slip boundary condition is used on the models and the bottoms, and the free surface is treated as a ＂moving wall＂ with zero shear force and the same velocity with inflow. In order to validate the simulation results, a particle image velocimetry（PIV） experiment is carried out to analyze the flow field. The numerical simulation results are consistent with the data obtained from experiment. The corresponding errors are all below 20%. Based on the validation, the effects of disposal space on flow field are simulated and analyzed. According to the simulation, in a parallel combination, a better artificial reef effect is obtained when the disposal space between two parallel reefs is 1.0L（L is the length of the combined three-tube reef model）. In a vertical combination, when the disposal space between two vertical reefs is 1.0L to 2.0L, the artificial reef effect is better.

Preliminary control of the air entrainment in bow wave based on the Liutex force method

Trails induced by air entrainment of bow wave breaking can be observed clearly around an advancing ship,making it prong to be detected and causing reduction in hydrodynamic performance.In breaking bow wave region,different scale of coherent vortex structures related closely to the air entrainment are generated.The formation and evolution of bubble clouds can be accounted partly by the swirling vortex flow of the jet plunging.In this work,high-fidelity simulation of the bow wave breaking around a rectangular thin plate is performed with the in-house code BAMR-SJTU.A Liutex force model is constructed to investigate the interaction between the free surface and vortices,and to explore the possibility of alleviating or controlling the air entrainment.This study is the first attempt to manipulate vortices corresponding to the air entrainment of the bow wave breaking.Some typical vortex structures based on the Liutex vortex identification method and the distribution of the vortex force are presented.Comparison of the vortex structures and the entrapped bubbles is conducted to illustrate the efficiency of Liutex force model in air entrainment control.