Investigations of the Performance on Vaned Diffusers for Low Specific Speed Centrifugal Compressor

Abstract

In this paper, the performance of vaned diffusers on low specific speed centrifugal compressors, was investigated experimentally and analytically. There is a problem of non-uniform distribution of the flow at impeller exit, as a factor to deteriorate the performance of the diffuser. This problem appears remarkably on the low specific speed type, because the blade height is relatively small and the flow inclines toward circumferential direction. The experiment was carried out with 2nd stage compressor of two-stage centrifugal type, focusing on the effect of number of diffuser vanes, vaneless ratio and throat area. Furthermore, unsteady fluid analysis was carried out by using Non Linear Harmonic method in order to understand about the phenomenon associated with the problem of non-uniform distribution of the flow. NOMENCLATURE A th throat area of diffuser AR area ratio of diffuser from throat to exit b blade height BL blockage factor (= 1-effective area / geometrical area) Cp static pressure recovery coefficient, Cp = (p-p 2) /(P 2-p 2) c v Specific heat at constant volume D diameter G mass flow ' non-dimensional flow, = G (R T 1) 0.5 / (D 2 2 P 1) ad Non-dimensional adiabatic head = adiabatic head / (RT 1) ad = { /(1)}(/(1) 1) M absolute Mach number ' Non-dimensional revolution speed ' = D 2 /(R T 1) 0.5 S specific speed (non-dimensional value) S = ' '0.5 / ad 3/4

Effect of Leading/Trailing Edge Swept Impeller on Flow Characteristics of Low Specific Speed Centrifugal Compressor

“…To further understand the complex aerodynamic performance of low specific speed centrifugal compressors, Methel et al [26] introduced in detail a new test facility called Centrifugal Stage for Aerodynamics Research (CSTAR). Zhang et al [27] and Kawanishi et al [28] investigated the geometric characteristics of impeller blades and diffuser blades in low specific speed centrifugal compressors, respectively, and derived the design rules and strategies for enhancing compressor aerodynamic performance. Zhang et al [29] also conducted research on the low specific speed centrifugal impeller with flow-trimming.…”