Masanao Kaneko

Mechanism of Blockage Generation in Transonic Centrifugal Compressor at Design and Off-Design Conditions

In a transonic centrifugal compressor, the loss generation is intensified by the formation of the shock wave and consequently the blockage is expected to increase. The blockage is considered to influence not only the flow rate and the increase of the static pressure but also the stall inception. However, the detailed mechanism of the blockage generation in the transonic centrifugal compressor has not been fully clarified.In this study, in order to clarify the mechanisms of loss and blockage generations in the transonic centrifugal compressor which are expected to be strongly influenced by the operating condition, the flows in the compressor at the off-design condition as well as at the design condition were analyzed numerically. The verifications of the computed results were carried out by comparing with available experimental results. The computed result clarified that the loss generation near the impeller inlet at design condition was mainly caused by the interactions of the shock wave with the tip leakage vortex appearing from the leading edge of the main blade as well as the boundary layer on the suction surface of the main blade. Moreover, these interactions were intensified by the decrease of the flow rate, and consequently enhanced the blockage effects by the tip leakage vortex from the leading edge of the main blade and resulted in the increase of the aerodynamic loss especially along the shroud surface in the impeller passage. On the other hand, the decrease of the blockage effects by the tip leakage vortex from the main blade with the increase of the flow rate formed the shock wave on the suction surface of the splitter blade at near-choke condition. This shock wave interacted with the tip leakage vortex from the splitter blade and consequently increased the aerodynamic loss.Copyright

20604 Numerical Analysis of Flow in Ultra Micro Centrifugal Compressor : Influence of Impeller Outlet Blade Angle

For an ultra micro centrifugal compressor, the applicability of two-dimensional (2D) blade has been investigated with the consideration of productivity in the downsizing of impeller. On the other hand, the improvement of the pressure recovery ratio in the diffuser is also required to increase the overall pressure ratio of a centrifugal compressor system. In this study, the flows in three types of centrifugal compressor impeller with the 2D blade which are different in the impeller outlet blade angle were analyzed numerically because the outlet blade angle is the most important design parameter to specify the shape of such impeller. The computed results clarified that the increase of impeller outlet blade angle reduces the tip leakage flow and the reversed flow at the impeller outlet, but increases the wall friction loss due to the increase of the cascade passage length.