Effects of fixed and dynamic mesh methods on simulation of stepped planing craft

In the present study,we investigate the effects of fixed and dynamic mesh methods on CFD simulation of stepped planing craft.To this accomplishment,three different body forms of without step,one step,and two step Cougar planing crafts are considered.Three-dimensional CFD analysis is conducted using finite volume method(FVM).Volume of fluid(VOF)model is used for free surface modeling.Overset mesh technique(dynamic mesh)and fixed mesh method are conducted by STAR CCM and ANSYS CFX CFD toolboxes,respectively.CFD results of total hydrodynamic resistance and dynamic trim angle are compared against our measured experimental data to assess the performance and accuracy of considered mesh methods.For more details,pressure distributions,wave patterns and streamlines around the hull models are also presented.Based on our CFD results,dynamic mesh method is more accurate and precise to simulate the stepped planing crafts compared to fixed mesh method.However,computational cost for dynamic mesh method is significantly greater than the fixed mesh method.We also found that the porpoising phenomenon is only detectable using dynamic mesh method in simulation of stepped Cougar planing craft.©2018 Shanghai Jiaotong University.Published by Elsevier B.V.

Shock-Wave/Rail-Fasteners Interaction for Two Rocket Sleds in the Supersonic Flow Regime

Rocket sleds belong to a category of large-scale test platforms running on the ground.The applications can be found in many fields,such as aerospace engineering,conventional weapons,and civil high-tech products.In the present work,shock-wave/rail-fasteners interaction is investigated numerically when the rocket sled is in supersonic flow conditions.Two typical rocket sled models are considered,i.e.,an anti-D shaped version of the rocket sled and an axisymmetric slender-body variant.The dynamics for Mach number 2 have been simulated in the framework of a dynamic mesh method.The emerging shock waves can be categorized as head-shock,tailing-shock and reflected-shock.An unsteady large-scale vortex and related shock dynamics have been found for the anti-D shaped rocket sled.However,a quasi-steady flow state exists for the slender-body shaped rocket sled.It indicates that the axisymmetric geometry is more suitable for the effective production of rocket sleds.With the help of power spectral density analysis,we have also determined the characteristic frequencies related to shock-wave/rail-fasteners interaction.Furthermore,a harmonic phenomenon has been revealed,which is intimately related to a shock wave reflection mechanism.