Analysis on slot-type casing treatment injection flow in an axial transonic compressor

Abstract

The purpose of this work is to understand the properties of the injection flow through slots opening surfaces with steady and unsteady simulations. The feasibility of evaluating slot effectiveness by steady results is demonstrated. Transient features of injection flow are detailed investigated. Numerical investigations are carried out in a 1.5 axial transonic compressor stage at a specified rotating speed with seven kinds of slot-type casing treatments. Comparisons between steady/unsteady results show that differences of overall performance and injection mass flow rate are dependent on simulation methods, rather than slot configurations. Thus, correlation analysis by steady results of seven slot configurations is considered valid and reveals strong linear correlation between injection mass flow and stall margin improvements/efficiency drops. Therefore, it is practical to evaluate the effectiveness of a specific slot configuration in this compressor with steady results by calculating injection mass flow rate. Afterwards, unsteady simulations are performed with a specific configuration of arc-curve skewed slots. It is clarified that the dividing locations between suction/injection regions moves along the axial direction based on the relative rotor/slots location. Exchanging flow through slots opening surfaces displays periodic variations over time. The variation cycle for one single slot equals blade passing period T. For summation of mass flow through all slots, the cycle equals to T divided by slots number in one passage. The net flow rate through all opening surfaces is always less than zero during a blading passing period, i.e. injection mass flow rate is larger than suction flow all the time.

Flow Control Methods and Their Applicability in Low-Reynolds-Number Centrifugal Compressors—A Review

“…Zhu et al [174] distinguished a linear correlation between the injection mass flow rate and stall margin improvement from numerical results.…”

“…Recently, the investigations have shown that, with the proper selection of casing treatment parameters, both the stall margin and the performance can be improved [170]. The most important design parameters for a self-circulating casing treatment are the width and position of the bleed slot [171][172][173], recirculation flow rate [172] and casing porosity [174].…”

“…. +0.15% + + [170] 2016 Recirculating slots AC 7.4-8.4% +2% +10% [174] 2016 Recirculating slots AC −2.71% +33.05% [169] 2015 Grooves CC ±0% +2.48% + [192] 2015 Injection nozzle CC 1.5% +37% [193] 2015 Injection nozzle CC 1-12% +30% [175] 2015 Injection tube Turbine blade 323,955 0.3-4% Reduction in total pressure loss [194] 2015 Recirculating slots AC − − +5.7% [195] 2013 Recirculating holes CC −1% −2% +10% [196] 2013 Recirculating slots CC 11% ±0% +20% [197] 2013 Recirculating slots CC −1% +17% [197] 2013 Recirculating slots with vanes CC +2% +4% + [198] 2012 Recirculating slots CC up to 13% ±0% + [198] 2012 Recirculating slots with vanes CC up to 17% ±0% + [173] 2012 Recirculating slots CC + [199] 2011 Recirculating holes CC −2 . .…”