In order to understand the mechanism of fluid flows in curved pipes, a large number of theoretical and experimental researches have been performed. As a critical parameter of curved pipe, the curvature ratioδhas received much attention, but most of the values ofδare very small (δ<0.1) or relatively small (δ≤0.5). As a preliminary study and simulation this research studied the fluid flow in a 90-degree curved pipe of large curvature ratio. The Detached Eddy Simulation (DES) turbulence model was employed to investigate the fluid flows at the Reynolds number range from 5000 to 20000. After validation of the numerical strategy, the pressure and velocity distribution, pressure drop, fluid flow, and secondary flow along the curved pipe were illustrated. The results show that the fluid flow in a curved pipe with large curvature ratio seems to be unlike that in a curved pipe with small curvature ratio. Large curvature ratio makes the internal flow more complicated; thus, the flow patterns, the separation region, and the oscillatory flow are different.

Abstract. Centrifugal fan is most widely used as an important component in ventilation system. The performance of centrifugal fan is sensitive to the inlet environment; therefore inlet flow distortion is one of the most attention problems. Numerical investigation has been carried out for the comparison of two kinds of inlet, one is standard straight duct and the other is a 90°curved duct. The results show that the distortion of inlet will seriously affect the impeller. Based on the theory of internal flow, a reasonable pressure gradient is added between the impeller and the curved duct, which is caused by inlet accelerator. Numerical simulation results show that acceleration can effectively suppress the inlet flow distortion; meanwhile it cannot affect the regular work of impeller.