A differential constraint method is used to obtain analytical solutions of a second-grade fluid flow. By using the first-order differential constraint condition, exact solutions of Poiseuille flows, jet flows and Couette flows subjected to suction or blowing forces, and planar elongational flows are derived. In addition, two new classes of exact solutions for a second-grade fluid flow are found. The obtained exact solutions show that the non-Newtonian second-grade flow behavior depends not only on the material viscosity but also on the material elasticity. Finally, some boundary value problems are discussed.
In this paper', the differences of turbulent coherent structure'betueen tire smooth and rough boundarr layers are analysed. Based on the discussing the transient properties from the smooth wall to the rough wall, the physical model of coherent structure for the rough botmdao" layer are established. The width of slowh'-moring turbulent spot and the bursting tone are obtained, which are in agreement with e.x'perfl~ental results.
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