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Global classical solution to 3D isentropic compressible Navier-Stokes equations with large initial data and vacuum

In this paper, we investigate the existence of a global classical solution to 3D Cauchy problem of the isentropic compressible Navier-Stokes equations with large initial data and vacuum. Precisely, when the far-field density is vacuum ($\widetildeρ=0$), we get the global classical solution under the assumption that $(γ-1)^\frac{1}{3}E_0μ^{-1}$ is suitably small. In the case that the far-field density is away from vacuum ($\widetildeρ>0$), the global classical solution is also obtained when $\left((γ-1)^\frac{1}{36}+\widetildeρ^\frac{1}{6}\right)E_0^{\frac{1}{4}}μ^{-\frac{1}{3}}$ is suitably small. The above results show that the initial energy $E_0$ could be large if $γ-1$ and $\widetildeρ$ are small or the viscosity coefficient $μ$ is taken to be large. These results improve the one obtained by Huang-Li-Xin in \cite{Huang-Li-Xin}, where the existence of the classical solution is proved with small initial energy. It should be noted that in the theorems obtained in this paper, no smallness restriction is put upon the initial data. It can be viewed the first result on the existence of the global classical solution to three-dimensional Navier-Stokes equations with large initial energy and vacuum when $γ$ is near $1$.