Wall-modeled large eddy simulation for the flows around an axisymmetric body of revolution

The flow around an axisymmetric body of revolution(DARPA SUBOFF bare model)at Re=1.2×10^(7)is numerically investigated using the wall-modeled large eddy simulation(WMLES).To evaluate the capabilities of WMLES in such wall-bounded turbulent flows,the effects of the wall stress model and sampling distance are systematically studied.The numerical results of the non-equilibrium wall stress model with an appropriate sampling distance are in good agreement with the experiments in terms of pressure coefficient,skin-friction coefficient,and drag coefficient.On this basis,the thickening of the turbulent boundary layer and the expansion of the wake can be clearly observed through flow visualization,especially using the Liutex vortex identification method.

Liutex-based centripetal force field model for improving the resistance and wake performances of JBC ship sailing in calm water

For complex aerodynamic and hydrodynamic problems,the analysis of vortex is very important.The Liutex method is an eigenvalue-based method which is local,accurate,and unique,which can give an accurate definition of vortex,so the control of vortex can be implemented and effectively guaranteed.Based on Liutex method,two methodologies of centripetal force model and counter-rotation force model were proposed to illustrate the vortex dynamics and possibly strengthen or weaken the vortices.In this paper,the Liutex-based centripetal force model is applied by adding a source term to the Navier-Stokes equations.In order to investigate the influence of the constructed Liutex force model on the 3-dimensional flow around a slow-fat ship,the calm-water drag calculation result of JBC ship is regarded as the initial flow field,and the new resistance and wake performances of the ship are obtained after applying the centripetal force model to the flow field with different strengths.Several views of the comparisons of the new steady flow fields are shown,and the parametric study results indicate that the Liutex-based centripetal force model can effectively change the resistance and wake performances of the JBC ship,which provides a new idea and theoretical basis for the comprehensive hydrodynamic performance optimization of the ship hull.

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.

Parametric study of Liutex-based force field models

The motion of fluid consists of different scales of coherent vortical structures.These vortical structures determine the characteristics of fluid motion and are key to understand fluid dynamics.In this paper,we study the fine control method of vortical structures based on the Liutex force field model.This is achieved by constructing a source term using Liutex and directly add it to the Navier-Stokes equations.To investigate the influence of the constructed Liutex force model on vortical structures,a flow past a cylinder at Reynolds number of 100 is numerically studied with different source term magnitude and region.The drag and lift forces on the cylinder,as well as the flow field near and behind the cylinder are compared and analyzed.Results show that Liutex force model can effectively strengthen or weaken the vortical structures based on different purpose.