Stall Margin Improvement in a Centrifugal Compressor through Inducer Casing Treatment

V V N K Satish Koyyalamudi,Quamber H Nagpurwala

doi:10.1155/2016/2371524

V V N K Satish Koyyalamudi, Quamber H Nagpurwala

Open Access

https://doi.org/10.1155/2016/2371524

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Abstract

The increasing trend of high stage pressure ratio with increased aerodynamic loading has led to reduction in stable operating range of centrifugal compressors with stall and surge initiating at relatively higher mass flow rates. The casing treatment technique of stall control is found to be effective in axial compressors, but very limited research work is published on the application of this technique in centrifugal compressors. Present research was aimed to investigate the effect of casing treatment on the performance and stall margin of a high speed, 4 : 1 pressure ratio centrifugal compressor through numerical simulations using ANSYS CFX software. Three casing treatment configurations were developed and incorporated in the shroud over the inducer of the impeller. The predicted performance of baseline compressor (without casing treatment) was in good agreement with published experimental data. The compressor with different inducer casing treatment geometries showed varying levels of stall margin improvement, up to a maximum of 18%. While the peak efficiency of the compressor with casing treatment dropped by 0.8%–1% compared to the baseline compressor, the choke mass flow rate was improved by 9.5%, thus enhancing the total stable operating range. The inlet configuration of the casing treatment was found to play an important role in stall margin improvement.

Highlights

Centrifugal compressors are widely used in various industries like oil and gas, aviation, refrigeration, and turbochargers
Computational Fluid Dynamics CAD (CFD) simulations on the baseline impeller were performed with different grid sizes, having 316800 elements (Grid-1), 397824 elements (Grid-2), 435200 elements (Grid-3), and 516864 elements (Grid-4), using ANSYS CFX software
The treatment slots of identical porosity were designed to follow the profile of the inducer tip section

Summary

Introduction

Centrifugal compressors are widely used in various industries like oil and gas, aviation, refrigeration, and turbochargers. Recent experimental studies by Alone et al [8,9,10] on the effect of axially bent casing treatment in a transonic axial compressor stage have shown that the treatment slot parameters like rotor tip axial coverage and porosity as well as the presence of a plenum behind the treatment slots significantly influence the compressor performance and its stalling characteristics. It may be noted that the inducer in a centrifugal compressor impeller behaves like an axial compressor rotor It is, hypothesized that casing treatment with slotted casing/shroud around the inducer tip region may be effective in controlling the suction surface and shroud boundary layers at low mass flow rate, delaying flow separation and delaying the onset of rotating stall, with resulting improvement in stall margin. The simulation results are presented in the form of global compressor performance and detailed flow behavior through impeller blade passages and casing treatment slots

Details of Centrifugal Compressor and Casing Treatment Configurations

Fluid Domain Discretization and Solver Settings

Results and Discussion

Conclusions