Thermodynamics Investigation and Spike-stall Identification Based on Energy Loss of Centrifugal Compressor

Abstract

Although quantities of investigations concerning the stall characteristics and thermal-dynamics of centrifugal compressor were carried out, rare discussions, however, were employed on the relationship between energy loss and flow unsteadiness, especially the losses originating from spike-type stall in the impeller. In the present work, a combined unsteady numerical and experimental analysis of energy loss features under stall condition in the impeller of centrifugal compressor was presented. Firstly, an energy loss prediction model based on one-dimensional equations considering multiple components was proposed and validated against experimental data. The dominating loss mechanisms in the impeller were quantitatively evaluated and the corresponding effect of each loss on various operating conditions was measured by proposing a weight coefficient. In order to prove the possibility of the potential application of the present approach, the weight coefficient method was also employed in another centrifugal compressor and the results were well validated. Then the incidence loss, which has the leading three weight coefficients during the occurrence of stall, were investigated with the distribution of inflow angle and entropy near stall condition. Then, applying blade loading variations and vortex transport analysis allowed the relevance of blade loading loss and clearance loss to be taken into account. Finally, with the synergy angles introduced, the criteria of spike stall through losses identification and qualification were established. The results imply that friction loss, clearance loss and incidence loss account for the major part of the total losses with the weight coefficient of 48%, 29% and 19% near stall condition. However, the weight coefficient of incidence loss increases remarkably with those of other losses decreasing from design condition to stall condition, indicating the significant contribution of incidence loss to the occurrence of stall. Correspondingly, the dramatic increase of inflow angle at limited circumferential region can be treated as a general criterion for spike-stall. The influence of tip clearance leakage on the leading edge of splitter blade results in the decrease of blade loading at reduced mass flow. Based on the synergy angle distribution, mutation region of field synergy angle accompanied with the increase of flow resistance at the impeller inlet may lead to a more efficient determination of the spike-stall for compressor impeller.