According to modeling principle that a model must be more accurate if including more flow information, and based on the Cauchy-Helmholtz theorem and the Smagorinsky model, a second-order dynamic model with double dynamic coefficients was proposed by applying dimension analyses. The Subgrid-Scale (SGS) stress is a function of both strain-rate tensor and rotation-rate tensor. The SIMPLEC algorithm and staggering grid system was applied to give the solution of the discretized governing equations, and for the turbulent flow through a 90° bend, the distributions of velocity and pressure were achieved. The comparison between experimental data and simulation results at a Reynolds number 40000 shows a good agreement and implies that this model is practicable and credible.