Abstract
A computational study has been conducted to analyze the performance of a centrifugal compressor under various levels of impeller-diffuser interactions. The study has been conducted using a low solidity vaned diffuser (LSVD), a conventional vaned diffuser (VD) and a vaneless diffuser (VLD). The study is carried out using Reynolds-Averaged Navier- Stokes simulations. A commercial software ANSYS CFX is used for this purpose. The extent of diffuser influence on impeller flow is studied by keeping the diffuser vane leading edge at three different radial locations. Detailed flow analysis inside the impeller passage shows that the strength and location of the wake region at the exit of impeller blade is heavily depended upon the tip leakage flow and the pressure equalization flow. Above design flow rate, the diffuser vane affects only the last twenty percent of the impeller flow. However, below design flow rate, keeping vane closer to the impeller can cause an early stall within the impeller. Small negative incidence angle at the diffuser vane is helpful in order to reduce the losses at the impeller exit.
Highlights
The nature of impeller exit flow has direct effects on the performance of the diffuser, thence the overall performance of compressor stage
Detailed flow analysis inside the impeller passage shows that the strength and location of the wake region at the exit of impeller blade is heavily depended upon the tip leakage flow and the pressure equalization flow
Below design flow rate, keeping vane closer to the impeller can cause an early stall within the impeller
Summary
The nature of impeller exit flow has direct effects on the performance of the diffuser, thence the overall performance of compressor stage. Hirsch et al and Kang and Hirsch observed that the location of the wake inside impeller results from a balance between the various secondary forces and the tip leakage. The nature of the secondary flow at the exit of the impeller, as observed by various researchers, is based on the vaneless diffuser. The effect of diffuser vane on impeller exit flow is not much investigated. Shum et al [10] investigated the upstream potential effect of the diffuser vanes on impeller tip leakage flow. Present study is aimed to investigate computationally the effects of diffuser vane on impeller exit flow. For comparison purpose a vaneless diffuser (VLD) is selected for the study
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