The particle paths predicted by a 3D CFD code for a conventionally designed vaned diffuser are presented in the figures below. The particles are colour coded depending on their point of origin, varying from blue at the hub to red at the tip as shown by the legend.
The particle paths indicate a complicated 3D flow pattern in the diffuser, and in particular the presence of a corner separation at the hub. This is due to the accumulation of low momentum fluid at the hub pressure surface corner, which then undergoes a strong positive pressure gradient. In order to improve the pressure recovery
in the diffuser, TURBOdesign1 was used to re-design the vanes using the loading distribution.
The flow leaving the (conventionally designed) impeller is non-uniform with a high velocity at the hub and a low (almost stagnant) velocity near the shroud wall. In the TURBOdesign1, predicted particle paths for the conventionally designed impeller.
The predicted particle paths for the impeller designed by TURBOdesign1 redesign, a fore-loaded distribution is used at the hub to increase diffusion, and aft-loading at the shroud is employed to avoid any flow separation.
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