Abstract
The work presents the results of a CFD campaign to investigate the impeller–diffuser interaction in a centrifugal compressor, taking advantage of experimental data from the open literature. Previous studies on the same turbomachine focused on an experimental investigation to understand the flow interaction between the impeller and the vaned diffuser. These experimental data have been used to validate the simulation approach and discuss its results. Several CFD models with increasing complexity have been developed to take into account different aspects. The steady analysis has been performed to highlight the potentials and limitations of such models and to carry out a first study of the flow. In order to analyze the impeller–diffuser interaction, a further model for the unsteady analysis has been set up. Two different operating points have been investigated: one on the surge limit and another in a more stable working zone. A good agreement with the experimental reference data has been obtained with the unsteady analysis and some insights in the complex flow field are deduced.
Highlights
The interaction between impeller and diffuser in centrifugal compressors is characterized by complex flow phenomena, which are still the focus of several research studies
The computational domain has been built on the basis of the geometrical coordinates of the hub, shroud and blade provided by Ziegler (2002) [20], for both the impeller and the vaned diffuser
The overall effect is a low energy fluid transport towards the shroud wall and the at the casing, the above secondary flows interact with the tip vortex (TV)
Summary
The interaction between impeller and diffuser in centrifugal compressors is characterized by complex flow phenomena, which are still the focus of several research studies. As long as the mixing process takes place rapidly, it cannot be completed in the vaneless space, so that unsteady effects are more or less significant, depending on the radial gap. Despite the mixing process taking place rapidly, in the vaneless space the unsteady effects of the impeller are not damped before the diffuser blade; these effects are significant and depend on the radial gap between impeller and diffuser vane. A previous study on this centrifugal compressor was presented in 2002 by Ziegler [20], who conducted an experimental investigation to understand the flow interaction between the impeller and the vaned diffuser. The second half of the paper is dedicated to the description of the numerical results, the comparison with experimental data and the discussion of the flow patterns, with special reference to the unsteady effects
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