Numerical Simulation Of Fluid Flow And Convective Heat Transfer In Bends

In this paper, the flow and convective heat transfer of Newtonian fluid and non-Newtonian power-law fluid in bends is taken as the research object, and numerical simulation is carried out by using a high-resolution code.The grid-independent solution is a premise of numerically studying turbulent convective heat transfer, while the appropriate treatment of boundary conditions is critical to the accuracy of numerical results. Therefore, this paper emphatically analyze the grid-independent solutions of velocity field and temperature filed. For the turbulent flow of Newtonian fluids, under the second type of boundary condition (heat flux condition) and by changing the mesh density, the influence of two treatments on the accuracy of numerical solutions is contrastively analyzed. For power-law fluid, the influence of Dn number, power-law index n and Pr number on the flow and convective heat transfer is studied.According to the simulation, it is observed that the numerical results of the flow and convective heat transfer of both Newtonian and power-law fluid in bends take great agreement with experiment data and analytical solutions. The study of grid-independent solutions show that because in incompressible flow the coupling of velocity and temperature fields is weak, the mesh size required for grid-independent solutions is different for the two fields.A finer mesh is needed for the grid-independent solution of the temperature field. In addition for the power-law fluid, the appearance of four vortices structure makes the flow more complex, in this case, the requirement of grid density for velocity field is relatively high.For turbulent flow of Newtonian fluid, the comparative analysis of the two treatments of the heat flux condition demonstrates that the algebraic formulation of Kader (1981) is in good agreement with experimental data even though the mesh is relatively coarse, so it has better versatility and grid adaptability. But the wall temperature gradient has a great effect on the calculation accuracy of Nu number, it is best to adopt the mesh scheme with small y+.For laminar flow of power-law fluid, Dn number has instability and the secondary flow jump to four vortices at uncertain Dn number. In the case of four vortices and the same Dn number, the velocity field is in good agreement with the predecessor’s result. By increasing Dn number, the effect on velocity field becomes less. Temperature field is mainly effected by Dn number and Pr number.