Effects of Degrees of Motion Freedom on Free-Fall of A Sphere in Fluid
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Free-fall of a sphere in fluid is investigated at a Galileo number of 204 by direct numerical simulations (DNS). We mainly focus on the effects of different degrees-of-freedom (DOFs) of the sphere motion during free-fall. The characteristics of free-fall are compared with those of flow past a fixed sphere. Additional numerical tests are conducted with constraints placed on the translational or rotational DOFs of the sphere motion to analyze different DOFs of sphere motion. The transverse motion contributes significantly to the characteristics of free-fall; it results in the retardation of the vortex shedding, leading to the decrease of the Strouhal number. In addition, the transversal sphere motion exhibits the tendency to promote the sphere rotation. On the contrary, the effects of the sphere rotation and vertical oscillations during free-fall are negligible.
Key wordsfree-fall direct numerical simulation degree of motion freedom
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The authors would like to thank Mr. WU Cheng-hao and Mr. HU Zhi-huan for their assistance in the CFD simulation. The numerical simulations were supported by the Center for HPC, Shanghai Jiao Tong University.
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