Abstract

To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k-ε turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both unsteady flow field and overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both overall performance data and local flow field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.

Highlights

  • Adding vanes in a vaneless diffuser in a centrifugal compressor improves efficiency and reduces working range (Yoshinaga et al [1], Flathers [2], Kmecl and Dalbert [3], and Cui [4])

  • The study was conducted in the perspective of compressor system and included both the overall performance and Unsteady Flows in a Transonic Centrifugal Compressor zx y (a)

  • Since the averaged Mach number is close to unity, the perturbations from the diffuser and volute do not propagate upstream to the impeller inlet

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Summary

INTRODUCTION

Adding vanes in a vaneless diffuser in a centrifugal compressor improves efficiency and reduces working range (Yoshinaga et al [1], Flathers [2], Kmecl and Dalbert [3], and Cui [4]). The overall performance changes of compressors with vaned diffusers can be obtained by integrating changes in the. Flow field caused by the diffuser vanes Both local pressure distribution and overall pressure recovery coefficients from simulation agree well with measurements. The study was conducted in the perspective of compressor system and included both the overall performance and Unsteady Flows in a Transonic Centrifugal Compressor zx y (a)

METHODOLOGY
OVERALL CHARACTERISTICS OF UNSTEADY FLOW
IMPELLER FLOW
DIFFUSER FLOW
VOLUTE FLOW
Findings
CONCLUSIONS

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