The existing simulation results for 2-DOF vortex-induced vibration are not satisfied,especially,the maximum amplitude estimation of its responses. In tests of Jauvtis & Williamson,the maximum amplitude of a cylinder with a low mass ratio could reach 1.5D,this phenomenon was named super upper branch. But,few simulation results of current studies can reach 1.3D even unable to capture super upper branch. The reasons were likely to be defects of the turbulence model itself and the unreasonable setting of numeri...