Global Power and Propulsion (GPPS): Montreal18 - Proceedings
Published May 7, 2018 | Version v1
Conference paper Open

Influence of Diffuser Diameter Ratio on the Performance of a Return Channel Within a Centrifugal Compressor Stage

Authors/Creators

  • 1. Institute of Jet Propulsion and Turbomachinery, RWTH Aachen University Germany
  • 2. MAN Diesel & Turbo SE Germany

Description

This paper describes the influence of the diffuser diameter ratio on the flow and the local loss mechanisms in the return channel of a single-shaft, high flow rate, multistage centrifugal compressor. The analysis, based on detailed measurements and numerical data of two diffuser diameter ratios, enables a deeper insight into the changed flow phenomena. The diffuser diameter ratio varied between d4/d2=1.75⁄and d4/d2=1.55⁄. The same design of the return system was used for both diffuser diameter ratios. Comprehensive experimental data was measured for a diffuser diameter ratio of d4/d2=1.75⁄on a single-stage centrifugal compressor test rig. As such, well-validated, numerical simulations complete the basis of this investigation. When the diffuser diameter ratio is reduced, the analysis reveals an operating point-dependent loss of up to 0.6% points stage efficiency, a decrease in the average circumferential flow angle at the stage exit and an increased variation in the flow angle. The flow inside the impeller and the first part of the vaneless diffuser is not influenced by the diffuser diameter ratio. The changes can therefore be linked to a shift in total pressure loss and static pressure recovery from the vaneless diffuser to the return system, so that the aerodynamic load on the return channel vanes increases. In addition, the flow conditions at the leading edge of the return channel vanes are influenced by the change inthe diffuser diameter ratio, which leads to higher, negative incidence in the hub region. A decreased solidity of the return channel vanes results in less flow turning and intensified secondary flow, which influences the circumferential flow angle at the stage exit. This paper describes a detailed investigation offlow behavior in a return channel when it is subjected to different diffuser diameter ratios and reveals the impact of this geometric change on the development of loss in the stator components and secondary flows in the return channel.

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References

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