Validation of Impeller-Diffuser Forced Response Excitations In Centrifugal Compressors

Abstract Vaned diffusers are commonly used in industrial centrifugal compressors to improve aerodynamic performance at the best efficiency flow point. At flow conditions away from the best efficiency point, vaned diffusers can result in a drop in performance when compared to their vaneless counterparts. The drop in performance arises primarily from the flow separation and wakes arising downstream of the vanes, resulting in an aerodynamic blockage in the diffuser. These wakes act as a forcing function and can result in a forced response characteristic on the rotor-bearing system. Understanding and quantifying the influence of these flow-induced forcing functions is therefore of importance for industrial centrifugal compressors. In this work, the influence of low solidity airfoil diffusers on rotor-bearing vibrations is assessed as observed on a high-pressure multi-stage inline centrifugal compressor. Transient CFD simulations were conducted to understand and quantify the nature of the forced response vibrations arising from the impeller-diffuser system. In addition, scaled testing was conducted on a single stage test rig equipped with dynamic pressure transducers in the diffuser flow path. The vaned diffuser was eventually implemented on an inline multi-stage centrifugal compressor for upstream oil & gas applications, and testing was performed in a closed loop environment to validate results. A qualitative comparison of forced response spectra results obtained from CFD versus test data is presented in this paper.