Effects of Swirl Distortion Induced by Bent-Torsion Ducts on Aerodynamic Performance of a Centrifugal Compressor

In order to investigate the effects of the swirl distortion induced by the bent-torsion intake duct on the aerodynamic performance of a centrifugal compressor, the numerical and experimental methods were carried out. The evolution processe of the outlet secondary flow structure with the torsional angle is clarified firstly. It is found that the swril form changes between the twin swirl and the offset swirl as the torsion angle increases. The bulk swirl appears approximately at the duct outlet when the torsion angle equals to 90°. Compared with the twin swirl, the shape of bulk swirl produces more obvious effects on the compressor performance. When the bulk swirl has the same rotational direction with the impeller at the design speed, both the pressure ratio and the efficiency decreases about 25%, and the surge flow also decreases. But when the bulk swirl has the opposite rotational direction with the impeller, the compressor performance has no obvious change and the compressor surge flow increases. The relationship among the swril angle, the swirl intensity and the relative flow angle of the blade at different span are investigated in details. The results indicate that both the angle and intensity of the swirl at the impeller inlet in different spans vary the relative flow angle of the blade leading edge and have significant effects on the intake attack angle.