Asymptotic Computational Fluid Dynamic (ACFD) Study of Three-Dimensional Turning Diffuser Performance by Varying Angle of Turn

The main problem in achieving high recovery for a tuning diffuser is flow separation which results in non-uniform flow distribution and excessive losses. Angle of turn is found to affect notably the performance of turning diffuser which its relationship is still unclear particularly for a 3-D case. The present work aims to numerically investigate the effect of varying turning angle, empty set = 30 degrees - 180 degrees on the performance of 3-D turning diffuser and to develop the performance correlations via integrating the turning angle using Asymptotic Computational Fluid Dynamics (ACFD) technique. Among all the turbulence models examined, the best validated results were obtained with the Reynold Stress Model with enhanced wall treatment of y(+) = 1.0 was applied for the intensive simulation. As the turning angle increased from 30 degrees to 180 degrees, the pressure recovery was reduced by 89.3% and the flow uniformity index was raised by 27.7%. Minimal flow separation took place at 0.75L(in)/W-1 of 90 degrees turning diffuser whereas maximum flow separation happened at 0.44L(in)/W-1 of 180 degrees turning diffuser. The performance correlations of 3-D turning diffuser as a function of geometrical and operating parameters was successfully developed using ACFD method. The ACFD results were kept within +/- 11.4% of deviation when compared with both CFD and experimental results.