This is the Part I of a two-part paper documenting the development of a novel asymmetric flow control method to improve the stability of a high-pressure-ratio turbocharger centrifugal compressor. Part I focuses on the non-axisymmetric flow in a centrifugal compressor induced by the non-axisymmetric geometry of the volute while Part II describes the development of asymmetric flow control method to avoid the stall on the basis of the characteristic of non-axisymmetric flow. To understand the asymmetries, experimental measurements and corresponding numerical simulation were carried out. The static pressure was measured by probes at different circumferential and stream-wise positions to gain insights about the asymmetries. The experiment results show that there is an evident non-axisymmetric flow pattern throughout the compressor due to the asymmetric geometry of overhung volute. The static pressure field in the diffuser is distorted at approximately 90° in rotational direction of the volute tongue throughout the diffuser. The magnitude of this distortion varies slightly with the rotational speeds. The magnitude of the static pressure distortion in the impeller is a function of the rotational speed. There is a significant phase shift between the static pressure distributions at the leading edge of the splitter blades and the impeller outlet. The numerical steady state simulation neglects the mentioned unsteady effects found in the experiments and can not predict the phase shift, but a detailed asymmetric flow field structure are obviously obtained.

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