Numerical calculation of turbulent flow in symmetric two-dimensional diffusers

This study presents numerical predictions on the fluid flow characteristics for turbulent flow ill symmetric two-dimensional diffusers. The grids are established by employing the nonorthogonal body-fitted coordinate system and associating them with the multi-block to handle the complex geometry. The turbulent governing equations are solved by the control-volume-based finite-difference method. The parameters studied include the entrance Reynolds numbers of the diffusers (Re = 6000, 9000 and 12000), the diffusion angle (theta = 22.5 degrees, 30 degrees, 60 degrees and 90 degrees), and the diffusers expansion ratio ER = 3. The numerical results show that the influence on the size of the recirculation region for turbulent now was ambiguous with Reynolds numbers effect, but evident with the change of diffusion angles. From the streamline contours, it can be seen that there is a large recirculation region on the top wall, and a small recirculation region is formed at the corner of the bottom wall, but the recirculation region of the bottom wall is ambiguous at theta = 22.5 degrees. In addition, with increasing Reynolds numbers or diffusion angle the pressure recovery coefficient C-PR decreases.