Numerical simulation of the self-propulsive motion of a fishlike swimming foil using the δ^+-SPH model

The present work is dedicated to the application of the recently developed （δ＋ -SPH） scheme to the self-propulsive fishlike swimming hydrodynamics. In the numerical method, a particle shifting technique （PST） is implemented in the framework of δ-SPH, combining with an adaptive particle refinement （APR） which is a numerical technique adopted to refine the particle resolution in the local region and de-refine particles outside that region. This comes into being the so-called δ＋- SPH scheme which contributes to higher numerical accuracy and efficiency. In the fishlike swimming modeling, a NACA0012 profile is controlled to perform a wavy motion mimicking the fish swimming in water. Thanks to the mesh-free characteristic of SPH method, the NACA0012 profile can undergo a wavy motion with large amplitude and move forward freely, avoiding the problem of mesh distortion. A parallel staggered algorithm is adopted to perform the fluidstructure interaction between the foil and the surrounding fluid. Two different approaches are adopted for the fishlike swimming problem. In Approach 1, the foil is fixed and flaps in a free stream and in Approach 2, the wavy foil can move forward under the self-driving force. The numerical results clearly demonstrate the capability of the δ＋ -SPH scheme in modeling such kind of self-propulsive fishlike swimming problems.

光滑粒子流体动力学框架下的EoSB空化模型及空化流动数值模拟研究

过去十余年来,光滑粒子流体动力学(Smoothed Particle Hydrodynamics,SPH)研究领域一直在探索空化流动的数值模拟,但迄今为止依然没有精确且稳定的SPH空化模型.本文将阐述一种在SPH框架内实现空化流动模拟的数值方法.首先,为了捕捉空化初生及其发展,本文在SPH框架内提出一种基于状态方程的相变模型.特别地,本文还引入一种粒子体积自适应算法(Volume Adaptive Scheme,VAS),以保证空化区域流体剧烈膨胀时粒子体积分布的均一性.此外,本文还采用粒子位移修正技术(Particle Shifting Technique,PST)和张力不稳定性控制技术(Tensile Instability Control,TIC)以提高粒子分布质量和抑制数值空洞的产生.最后,本文还通过引入大涡模拟(Large Eddy Simulation,LES)模型以考虑湍流效应,提高本文提出的SPH空化模型对高雷诺数流动的适用性.研究结果表明,本文提出的基于SPH方法的新空化模型能实现空化区域和压力分布等问题的精确预报.