Stability Improvement of High-Pressure-Ratio Turbocharger Centrifugal Compressor by Asymmetric Flow Control: Part I—Non-Axisymmetric Flow in Centrifugal Compressor

Abstract

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.

Effects of volute’s asymmetry on the performance of a turbocharger centrifugal compressor

“…This phenomenon has long been recognized in both experiments and numerical simulations, [1][2][3] and its effects on the performance of centrifugal compressors were widely studied. [4][5][6] The experiments and numerical simulations conducted by Yang et al 4 confirmed that the pressure distortion induced by the volute extended upstream to the impeller inlet, implying that the impeller was subjected to varying inlet and exit conditions, which led to the deterioration of the performance. Zheng et al 5 compared performance of a high pressureratio centrifugal compressor with and without the volute using three-dimensional viscous computational fluid dynamics (CFD).…”

“…Yang et al 4 compared the static pressure distribution in the vaneless diffuser and the impeller captured by steady simulation with frozen-rotor method and S-A model, and experimental measurements, as shown in Figure 5. It can be seen that the steady simulation with ''frozen-rotor method'' well predicted the phase (location of the minimum) and the magnitude of the static pressure distribution at the impeller outlet ( Figure 5(a)), as well as the magnitude of the static pressure distribution within the impeller ( Figure 5(b)).…”

“…where g ¼ dG=dm 4 The four equations (13), (15), (16), and (18) define the perturbations for the compression system with four effective variables, namely m 3 , m 4 , P 3 , and P 4 . Based on these four equations, a second-order ordinary differential equation can be obtained in terms of any one of the four variables as follows…”

A Study on the Stall Detection of an Axial Compressor through Pressure Analysis

“…In other words, the inlet pressure and outlet pressure of the compressor could reflect compressor performance, to a certain extent. In order to investigate the relationship between the compressor pressure and performance, the study of the compressor requires massive numerical simulations and experiments [8,9].…”

Investigation of the instability mechanisms in a turbocharger centrifugal compressor with a vaneless diffuser by means of unsteady simulations

“…The asymmetric volute is usually designed as a spiral-shaped overhung housing that acts as a diffuser at lower flow rates but as a nozzle at higher flow rates than the design values. This situation causes an asymmetric pressure distribution in the diffuser exit, which has a significant impact on the upstream components 31–33 and even on the impeller by reducing the performance, particularly in the stable flow range. Zheng et al 34 reported numerical estimations of the impact of the asymmetric volute on the stability of a turbocharger centrifugal compressor with a vaneless diffuser and found that the stable flow range was constricted by up to 42% at the design speed, indicating that the volute harms the flow stability severely.…”